外文翻译--计算机

外文资料Database Management SystemsA database (sometimes spelled data base) is also called an electronic database , referring to any collection of data, or information, that is specially organized for rapid search and retrieval by a computer. Databases are structured to facilitate the storage, retrieval , modification, and deletion of data in conjunction with various data-processing operations .Databases can be stored on magnetic disk or tape, optical disk, or some other secondary storage device.A database consists of a file or a set of files. The information in these files may be broken down into records, each of which consists of one or more fields. Fields are the basic units of data storage , and each field typically contains information pertaining to one aspect or attribute of the entity described by the database . Using keywords and various sorting commands, users can rapidly search , rearrange, group, and select the fields in many records to retrieve or create reports on particular aggregate of data.Complex data relationships and linkages may be found in all but the simplest databases .The system software package that handles the difficult tasks associated with creating ,accessing, and maintaining database records is called a database management system(DBMS).The programs in a DBMS package establish an interface between the database itself and the users of the database.. (These users may be applications programmers, managers and others with information needs, and various OS programs.)A DBMS can organize, process, and present selected data elements form the database. This capability enables decision makers to search, probe, and query database contents in order to extract answers to nonrecurring and unplanned questions that aren’t available in regular reports. These questions might initially be vague and/or poorly defined ,but people can “browse”through the database until they have the needed information. In short, the DBMS will “manage” the stored data items and assemble the needed itemsfrom the common database in response to the queries of those who aren’t programmers.A database management system (DBMS) is composed of three major parts:(1)a storage subsystem that stores and retrieves data in files;(2) a modeling and manipulation subsystem that provides the means with which to organize the data and to add , delete, maintain, and update the data;(3)and an interface between the DBMS and its users. Several major trends are emerging that enhance the value and usefulness of database management systems;Managers: who require more up-to-data information to make effective decisionCustomers: who demand increasingly sophisticated information services and more current information about the status of their orders, invoices, and accounts.Users: who find that they can develop custom applications with database systems in a fraction of the time it takes to use traditional programming languages.Organizations : that discover information has a strategic value; they utilize their database systems to gain an edge over their competitors.The Database ModelA data model describes a way to structure and manipulate the data in a database. The structural part of the model specifies how data should be represented(such as tree, tables, and so on ).The manipulative part of the model specifies the operation with which to add, delete, display, maintain, print, search, select, sort and update the data.Hierarchical ModelThe first database management systems used a hierarchical model-that is-they arranged records into a tree structure. Some records are root records and all others have unique parent records. The structure of the tree is designed to reflect the order in which the data will be used that is ,the record at the root of a tree will be accessed first, then records one level below the root ,and so on.The hierarchical model was developed because hierarchical relationships are commonly found in business applications. As you have known, an organization char often describes a hierarchical relationship: topmanagement is at the highest level, middle management at lower levels, and operational employees at the lowest levels. Note that within a strict hierarchy, each level of management may have many employees or levels of employees beneath it, but each employee has only one manager. Hierarchical data are characterized by this one-to-many relationship among data.In the hierarchical approach, each relationship must be explicitly defined when the database is created. Each record in a hierarchical database can contain only one key field and only one relationship is allowed between any two fields. This can create a problem because data do not always conform to such a strict hierarchy.Relational ModelA major breakthrough in database research occurred in 1970 when E.F. Codd proposed a fundamentally different approach to database management called relational model ,which uses a table as its data structure.The relational database is the most widely used database structure. Data is organized into related tables. Each table is made up of rows called and columns called fields. Each record contains fields of data about some specific item. For example, in a table containing information on employees, a record would contain fields of data such as a person’s last name ,first name ,and street address.Structured query language(SQL)is a query language for manipulating data in a relational database .It is nonprocedural or declarative, in which the user need only specify an English-like description that specifies the operation and the described record or combination of records. A query optimizer translates the description into a procedure to perform the database manipulation.Network ModelThe network model creates relationships among data through a linked-list structure in which subordinate records can be linked to more than one parent record. This approach combines records with links, which are called pointers. The pointers are addresses that indicate the location of a record. With the network approach, a subordinate record can be linked to a key record and at the same time itself be a key record linked to other sets of subordinate records. The network mode historically has had a performanceadvantage over other database models. Today , such performance characteristics are only important in high-volume ,high-speed transaction processing such as automatic teller machine networks or airline reservation system.Both hierarchical and network databases are application specific. If a new application is developed ,maintaining the consistency of databases in different applications can be very difficult. For example, suppose a new pension application is developed .The data are the same, but a new database must be created.Object ModelThe newest approach to database management uses an object model , in which records are represented by entities called objects that can both store data and provide methods or procedures to perform specific tasks.The query language used for the object model is the same object-oriented programming language used to develop the database application .This can create problems because there is no simple , uniform query language such as SQL . The object model is relatively new, and only a few examples of object-oriented database exist. It has attracted attention because developers who choose an object-oriented programming language want a database based on an object-oriented model.Distributed DatabaseSimilarly , a distributed database is one in which different parts of the database reside on physically separated computers . One goal of distributed databases is the access of information without regard to where the data might be stored. Keeping in mind that once the users and their data are separated , the communication and networking concepts come into play .Distributed databases require software that resides partially in the larger computer. This software bridges the gap between personal and large computers and resolves the problems of incompatible data formats. Ideally, it would make the mainframe databases appear to be large libraries of information, with most of the processing accomplished on the personal computer.A drawback to some distributed systems is that they are often based on what is called a mainframe-entire model , in which the larger host computeris seen as the master and the terminal or personal computer is seen as a slave. There are some advantages to this approach . With databases under centralized control , many of the problems of data integrity that we mentioned earlier are solved . But today’s personal computers, departmental computers, and distributed processing require computers and their applications to communicate with each other on a more equal or peer-to-peer basis. In a database, the client/server model provides the framework for distributing databases.One way to take advantage of many connected computers running database applications is to distribute the application into cooperating parts that are independent of one anther. A client is an end user or computer program that requests resources across a network. A server is a computer running software that fulfills those requests across a network . When the resources are data in a database ,the client/server model provides the framework for distributing database.A file serve is software that provides access to files across a network. A dedicated file server is a single computer dedicated to being a file server. This is useful ,for example ,if the files are large and require fast access .In such cases, a minicomputer or mainframe would be used as a file server. A distributed file server spreads the files around on individual computers instead of placing them on one dedicated computer.Advantages of the latter server include the ability to store and retrieve files on other computers and the elimination of duplicate files on each computer. A major disadvantage , however, is that individual read/write requests are being moved across the network and problems can arise when updating files. Suppose a user requests a record from a file and changes it while another user requests the same record and changes it too. The solution to this problems called record locking, which means that the first request makes others requests wait until the first request is satisfied . Other users may be able to read the record, but they will not be able to change it .A database server is software that services requests to a database across a network. For example, suppose a user types in a query for data on his or her personal computer . If the application is designed with the client/server model in mind ,the query language part on the personal computer simplesends the query across the network to the database server and requests to be notified when the data are found.Examples of distributed database systems can be found in the engineering world. Sun’s Network Filing System(NFS),for example, is used in computer-aided engineering applications to distribute data among the hard disks in a network of Sun workstation.Distributing databases is an evolutionary step because it is logical that data should exist at the location where they are being used . Departmental computers within a large corporation ,for example, should have data reside locally , yet those data should be accessible by authorized corporate management when they want to consolidate departmental data . DBMS software will protect the security and integrity of the database , and the distributed database will appear to its users as no different from the non-distributed database .In this information age, the data server has become the heart of a company. This one piece of software controls the rhythm of most organizations and is used to pump information lifeblood through the arteries of the network. Because of the critical nature of this application, the data server is also the one of the most popular targets for hackers. If a hacker owns this application, he can cause the company's "heart" to suffer a fatal arrest.Ironically, although most users are now aware of hackers, they still do not realize how susceptible their database servers are to hack attacks. Thus, this article presents a description of the primary methods of attacking database servers (also known as SQL servers) and shows you how to protect yourself from these attacks.You should note this information is not new. Many technical white papers go into great detail about how to perform SQL attacks, and numerous vulnerabilities have been posted to security lists that describe exactly how certain database applications can be exploited. This article was written for the curious non-SQL experts who do not care to know the details, and as a review to those who do use SQL regularly.What Is a SQL Server?A database application is a program that provides clients with access todata. There are many variations of this type of application, ranging from the expensive enterprise-level Microsoft SQL Server to the free and open source mySQL. Regardless of the flavor, most database server applications have several things in common.First, database applications use the same general programming language known as SQL, or Structured Query Language. This language, also known as a fourth-level language due to its simplistic syntax, is at the core of how a client communicates its requests to the server. Using SQL in its simplest form, a programmer can select, add, update, and delete information in a database. However, SQL can also be used to create and design entire databases, perform various functions on the returned information, and even execute other programs.To illustrate how SQL can be used, the following is an example of a simple standard SQL query and a more powerful SQL query:Simple: "Select * from dbFurniture.tblChair"This returns all information in the table tblChair from the database dbFurniture.Complex: "EXEC master..xp_cmdshell 'dir c:\'"This short SQL command returns to the client the list of files and folders under the c:\ directory of the SQL server. Note that this example uses an extended stored procedure that is exclusive to MS SQL Server.The second function that database server applications share is that they all require some form of authenticated connection between client and host. Although the SQL language is fairly easy to use, at least in its basic form, any client that wants to perform queries must first provide some form of credentials that will authorize the client; the client also must define the format of the request and response.This connection is defined by several attributes, depending on the relative location of the client and what operating systems are in use. We could spend a whole article discussing various technologies such as DSN connections, DSN-less connections, RDO, ADO, and more, but these subjects are outside the scope of this article. If you want to learn more about them, a little Google'ing will provide you with more than enough information. However, the following is a list of the more common itemsincluded in a connection request.Database sourceRequest typeDatabaseUser IDPasswordBefore any connection can be made, the client must define what type of database server it is connecting to. This is handled by a software component that provides the client with the instructions needed to create the request in the correct format. In addition to the type of database, the request type can be used to further define how the client's request will be handled by the server. Next comes the database name and finally the authentication information.All the connection information is important, but by far the weakest link is the authentication information—or lack thereof. In a properly managed server, each database has its own users with specifically designated permissions that control what type of activity they can perform. For example, a user account would be set up as read only for applications that need to only access information. Another account should be used for inserts or updates, and maybe even a third account would be used for deletes. This type of account control ensures that any compromised account is limited in functionality. Unfortunately, many database programs are set up with null or easy passwords, which leads to successful hack attacks.译文数据库管理系统介绍数据库（database,有时拼作data base）又称为电子数据库，是专门组织起来的一组数据或信息，其目的是为了便于计算机快速查询及检索。

英文部分Computerized tooth profile generation of elliptical gea rs manufactured by shaper cuttersBiing-Wen BairDepartment of Mechanical Engineering, National Lien Ho Institute of T ech nology,AbstractThis work sim ula tes an elliptical gear driv e,the a xis of rot at ion of wh ich is coincident wi th its geometric center, manufac tured by sh ape r cutters. The mathematical model of an elliptical gear is developed based on the theory of gearing and gear generation mechanisms. In addition, the tooth undercutting of the gear is also investigated based on the developed mathematical model of the elliptical gear, its unit normal vectors and a numerical method.A geometric relationship is developed and applied to prevent the occurrence of pointed teeth on elliptical gears. Further, this study also develops computer simulation programs to generate the tooth profile of elliptical gears without tooth undercutting and pointed teeth. Compa rison of the angula r ve locity variations of the elliptical gear dr i ves is al so ma de. Th e r e su lts show that the deve lope d elliptica l gear driv e can be utilized as an oil pump with a larger pumping volume and less angular velocity variation. © 2002 Elsevier Science B.V. All rights reserved.Keywords: Elliptical gears; Undercutting; Pointed teeth1. IntroductionAn elliptical gear drive, the rotation center of which coincides with one of its foci, is kinematically equivalent to the crossed link, and can be used to produce irregular rotations. In addition, it is well known for providing excellent characteristics such as accurate transmission, compact size, and ease of dynamic balance. Hence, elliptical gear drives have been applied successfully in various types of automatic machinery, quick-return mechanisms, packaging machines, and printing presses [1]. This type of gearing can also be used to develop non-circular gears, which belong to high-order elliptical pitch curves. Second- order elliptical gear drives, the rotation center of which coincides with one of its foci, can find use in the design of instruments such as pumps and flow meters [1]. However, this type of gear set has two speed changes for each revolution, these two-cycle variations inducing a wave fluctuationthat is so severe that the second-order elli p tical gear set cannot be used as oil pumps for steady o il pumping.The design and manufacture of an elliptical gear are difficult because the pitch curve of the gear is an ellipse.Some studies [2—6] have focused on kinematic analysis and computer-aided design of elliptical pitch curves. Kuczewski [7] used a spur gear to approximate the profile of an elliptical gear. Emura and Arakawa [8] used an elliptical gear to analyze a steering mechanism, where this steering mechan- ism can turn a carrier with a small radius. Also, Freudenstein and Chen [9] developed variable-ratio chain drives (e.g. elliptical gear drives), which were applied to bicycles and variable motion transmissions involving band drives, tape drives, and time belts with a minimum slack. Moreover, Litvin [10] adopted the concept of evolute curves to form the tooth profile, and also derived the tooth evolute of an ellipse. Chang and Tsay [11] used a shaper cutter and applied the inverse mechanism relationship and the equation of meshing to produce the mathematical model of elliptical gears, the rotation center of which turns around one of its foci. Also, Chang et al. [12] used a rack cutter and the same method to produce the mathematical model and undercut- ting conditions of the same type of elliptical gears. However, when the elliptical gear surfaces are generated by shaper cutters, pointed teeth may appear and the tooth addendum is reduced. Pedrero et al. [13] proposed an approximation method for modifying the tooth addendum and contact ratio, and computer simulation results also show that the gear contact ratio depends on the tooth addendum. Additionally, Liou et al. [14] analyzed spur gears with low contact ratios (a contact ratio of less than 2) and high contact ratios (equal or larger than 2) when subjected to dynamic loads by applying the NASA gear dynamics software DANST. The DANST program determined the instantaneous contact teeth and contact ratio based on the gear average stiffness, commonly referred to as mesh stiffness. Recently, Bair and Tsay [15] proposed a tooth contact analysis (TCA) program to calculate the instantaneous contact teeth and average contact ratio of a dual-lead worm gear drive. The DANST and TCA methods confirm that reducing the gear addendum results in the decrease of the gear instantaneous contact teeth and the average contact ratio.Based on the position of the rotation center, elliptical gear drives fall into two types: the elliptical gear which rotates about its geometric center (type 1); the elliptical gear which rotates around one of its elliptical foci. An n- order driven non-circular gear, of which therotation axis is one of its foci, is one in which the driving elliptical gear performs n revolutions for one revolution of the driven non- circular gear. A second-order elliptical gear (type 2) is defined as n = 2. Under the same eccentricity and major axis, the size of the type 1 elliptical gears is smaller than that of the type 2. Further, if the type 1 elliptical gear set is applied to oil pumps, the wave fluctuation of the pumping oil is smaller and smoother than that of the other type. The elliptical gear tooth profile is usually produced by a hob- bing or shaping machine with a hob cutter or shaper cutter. This study simulates the manufacture of elliptical gears via a shaper cutter on a shaping machine. It is known that if a spur gear is produced by a shaper, the profile of the shaper cutter should be the same as that of the mating spur gear. Therefore, the mathematical model of a shaper cutter is the same as that of a spur gear, which can be derived from the generation mechanism with a rack cutter. According to the theory of gearing, the mathematical models of elli p tical gear tooth profiles, which rotate about their geometric center (type 1), are developed based on the proposed generation mechanism with shaper cutters. Due to the complex characteristics of this type of elliptical gear, undercutting and pointed teeth may exist on its tooth profile. The tooth undercutting of this type of elliptical gear is affected by its pressure angle, number of teeth, module, and major axis. The strength of the gear tooth root can be increased by applying a positive-shifted modification for the cutter during the gear generation. However, an over-positive-shifted modification may result in the appear- ance of pointed teeth. Pointed teeth are generated when the right- and left-side involute tooth profiles intersect on or below the addendum circle of the gear. Further, the pointed teeth are usually generated on the two major axis of an elliptical gear. If a profile index is defined to prevent pointed teeth generation on the two major axis of an elliptical gear, then no other pointed tooth will be generated for all elliptical gear profiles. Thus, the computer program developed here can calculate and provide proper design parameters for the designed elliptical gears to avoid tooth undercutting and pointed teeth.2. Mathematical model of the elliptical gear surfacesShaper cutters are used to generate elliptical gears, and the profiles of shaper cutters are the same as those of spur gears. Hence, the mathematical model of the shaper cutter is the same as that of the spur gear, which is generated from rack cutters. A complete elliptical gear tooth profile consists of three surface regions, i.e. the working region, the fillet and the bottom land. Therefore, the profile parameters of a shaper cutter can be represented by theparameters of a rack cutter. Fig. 1 shows three regions of a rack cutter 2p including the working region, the fillet and the top land, used for shaper cutter and elliptical gear generations. When the shaper cutter creates the elliptical gear in a cutting mechanism, its center rotates along the Z c-axis and translates along the X c and Y c-a xes, performing a pure roll without sliding on the pitch ellipse, and the gear blank is rotated about its geometric center 01 as in Fig.2.2.1. Working region of shaper cutter profileFig. 1 presents the design of the normal section of rack cutter 2p, where regions 3 and 4 are the left- and right-side working regions, regions 2and 5 are the left- and right-side fillets, and regions 1 and6 are the left- and right-side top lands. Meanwhile, parameter £p = M0M1 is a design parameter, expressing the distance measured from the initial point M0 to an arbitrary point M1 in the working region. The three- dimensional rack cutter profile can be obtained by translating its normal section, presented in Fig. 1, along the Z r-a xis with a displace me nt para meter U p. The refore, by applying the theory of gearing, the mathematical model of the working region of the shaper cutter can be represented in the coordinate system S c (X c , Y c , Z c ) by the following equation (Litvin, 1989):Fig. 1. Normal section of a rack cutter 2p for generating the driving shaper cutter.Fig. 2. Kinematic relationship between the shaper cutter and the generated gear.where A0 is the design parameter used to determine the addendum of the shaper, B0 the tooth width of the shaper, r s the pitch radius of the shaper, c c the generated angle of the shaper and i/i n the pressure angle as shown in Fig. 1. In Eq. (1), the upper sign indicates the right-side shaper surface while the lower sign represents the left-side shaper surface. The normal vector of the working region of the shaper cutter surface can be obtained as follows:2.2. Locus of the shaper cutterFig. 2displays the kinematic relationship between the shaper cutter and the generated elliptical gear. During the elliptical gear generation, the shaper cutter rotates about the Z c-axis and translates along a curve that keeps the shaper centrode and elliptical pitch of the generated gear in tangency at their instantaneous pitch point, I. The coordinate systems displayed in Fig. 2are the Cartesian coordinate system with right-handed three mutual perpendicular axes. It is noted that the Z-axis is not shown for simplicity. Coordinate system S c (X c , Y c , Z c ) is attached to the shaper cutter, and coordinate system S1(X1, Y1, Z1) is attached to the generated elliptical gear of which the rotation center is coincident with the gear geometric center. Parameter y1 is the angle formed by the X1-axis and the tangent line which corresponds to the tangency of the shaper centrode and elliptical pitch at their instantaneous pitch point, I. The rotation angle of the elliptical gear is 7t/2—y1, and anglec1 is a function of y1. Parameter c s, measured from the line0c I to the Y c-axi s of the shaper cutter, represents the rota- tional angle of the shaper. Let R1 denotes the position vector of the generated elliptical gear profile and R c represents the position vector of the shaper cutter surface. By applying thefollowing homogeneous coordinate transformation matrix equation, the locus (family) of the shaper cutter represented in coordinate system S1 can be obtained as follows:Substituting Eq. (1) into Eq. (3) provides the locus of shaper surfaces represented in coordinate system S1 as follows:Fig. 3. Tangent line of the ellipse.and the corresponding normal vector can also be obtained by:WhereIn Eq. (6), parameter 21 is the eccentricity of the ellipse, a1 the major semi-axis and b1 the minor semi-axis. Expressing the pitch curve of the elliptical gear, r1(c1), using the Cartesian coordinate system, the x1 and y1 compone nts along the coordinate axes are: AndReferring to Fig. 3, the unit tangent vector to the pitch curve at point I is positive in the fourth quadrant. The tangent vector of the pitch curve can be obtained by differentiating Eqs.(7) and (8) with respect to parameter c1 and then normalizing the results. This process results in the unit tangent vector of the pitch curve as follows:As Fig. 3 indicates, the unit tangent vector t1 of the pitch curve can also be represented in terms of angle y1 by the following equation:According to Eqs. (9) and (10), angle y1 can be expressed in terms of c1 as follows：AndAs shown in Fig. 2, the arc length of the shaper cutter, measured from the starting point N to the instantaneous pitch point I along the circular pitch, is equal to the arc length measured from the starting point M to the instantaneous pitch point I along the pitch ellipse. According to integral operation, the arc length can be expressed as follows:中文翻译计算机控制插齿刀加工椭圆齿轮齿形白炳文国立联合大学机械工程系摘要这个工作是模拟椭圆齿轮传动,轴围绕其几何中心旋转,用插齿刀加工。

Computer-aided Design and Computer-aided Manufacturing(CAD／CAM)Throughout the history of our industrial society，many invention have been patented and whole new technologies have evolved .Whitney is concept of interchangeable parts，Watt’s steam engine，and Ford is assembly line are but a few developments that are most noteworthy during our industrial period . Each of these developments has impacted manufacturing as we know it，and has earned these individuals deserved recognition in 0ur history hooks. Perhaps the single development that has impacted manufacturing more quickly and significantly than any previous technology is the digital computer.Since the advent 0f computer technology, manufacturing professionals have wanted to automate the design process and use the database developed therein for automating manufacturing processes. Computer—aided design／computer-aided manufacturing (CAD／CAM)，when successfully implemented, should remove the “wall” that has traditionally existed between the design and manufacturing components .CAD／CAM means using computers in the design and manufacturing processes. Since the advent of CAD／CAM，other terms have developed:Computer graphics(CG)Computer—aided engineering(CAE)Computer-aided design and drafting(CADD)Computer aided process planning(CAPP)These spin-off terms a11 refer to specific aspects of the CAD／CAM concept CAD／CAM itself is a broader，more inclusive term. It is at the heart of automated and integrated manufacturing.A key goal of CAD／CAM is to produce data that can be used in manufacturing a product while developing the database for the design of that product When successfully implemented, CAD／CAM involves the sharing of a common database between the design and manufacturing components of a company,Interactive computer graphics (ICG) plays an important role in CAD/CAM, Though the use of ICG, designers develop a graphic image of the product being designed while storing the data that electronically make up the graphic image. The graphic image can be presented in a two-dimensional (2+D) , three-dimensional(3-D),or solids format. ICG image are constructed using such basic geometric characters as points, lines, circles, and curves. Once created, these images can be easily edited and manipulated in a variety of ways including enlargements,reductions, rotations, and movements.An lCG system has three main components :1 ) hardware, which consists of the computer and various peripheral devices; 2) software, which consists of the computer programs and technical manuals for the system ; and 3) the human designer, the most important of the three components.A typical hardware configuration for an ICG System include a computer，a display terminal, a disk drive unit for floppy diskettes, a hard disk, or both; and input/output devices such as a keyboard，plotter, and printer. These devices, along with the software, are the tools modern designers use to develop and document their designs.The ICG systems could enhance the design process by allowing the human designer to focus on the intellectual aspects of the design process, such as conceptualization and making judgment-based decisions. The computer performs tasks for which it is better suited, such as mathematical calculations, storage and retrieval of data，and various repetitive operations such as crosshatching.Rationale for CAD／CAMThe rationale CAD／CAM is similar to that used to justify any technology-based improvement in manufacturing . It grows out of a need to continually improve productivity，quality．and，in turn competitiveness. There are also other reasons why a company might make a conversion from manual processes to CAD／CAM:increased productivitybetter qualitybetter communicationcommon database with manufacturingreduced prototype construction costsfaster response to customersIncreased ProductivityProductivity in the design process is increased by CAD／CAM. Time-consuming tasks such as mathematical calculations．data storage and retrieval, and design visualization are handled by the computer，which gives the designer more time to spend on conceptualizing and completing the design. In addition, the amount of time required to document a design can be reduced significantly with CAD／CAM. All of these taken together means a shorter design cycle, shorter overall project completion time, and a higher level of productivity.Better QualityBecause CAD／CAM allows designers to focus more on actual design problems and lesson time-consuming，nonproductive tasks，product quality improves with CAD／CAM. CAD ／CAM allows designers to examine a wider range of design alternatives and to analyze each alternative more thoroughly before selecting one. In addition, because labor-intensive tasks are performed by the computer, fewer design errors occur. These all lead to better product quality.Better CommunicationDesign documents such as drawings，parts lists, bills of material, and specifications are tools used to communicate the design to those who will manufacture it. The more uniform , standardized, and accurate these tools are, the better the communication will be. Because CAD/CAM leads to more uniform, standardized, and accurate documentation, it improves communication.Common DatabaseThis is one of the most important benefits of CAD／CAM. With CAD／CAM．the data generated during the design of product can be use in product the product. This sharing of a common database helps to eliminate the age-old “wall” separating the design and manufacturing functionReduced Prototype CostsWith manual design，models and prototypes of a design must be made and tested, adding to the cost of the finished product. With CAD／CAM，3-D computer models can reduce and, in some case, eliminate the need for building expensive prototypes. Such CAD／CAM capabilities as solids modeling allow designers to substitute computer models for prototypes in many cases.Faster Response to CustomersResponse time is critical in manufacturing. How long does it take to fill a customer’s order? The shorter the time, the better it is. A fast response time is one of the keys to being more competitive in an increasingly competitive marketplace. Today, the manufacturer fastest response time is as likely to win a contract as the one with the lowest bid. By shortening the overall design cycle and improving communication between the design and manufacturing components, CAD／CAM can improve a company’s response timeHistorical Development of CAD／CAMThe historical development of CAD／CAM has followed close behind the development of computer technology and has paralleled the development of ICG technology. The significant developments leading to CAD／CAM began in the late 1950s and early 1960s. The first of these was the development, at Massachusetts Institute of Technology (MIT)，ofthe Automatically Programmed Tools (APT) computer programming language.The purpose of APT was to simplify the development of parts programs for numerical control machines. It was the first computer language to be used for this purpose. The APT language represented a major step toward automation of manufacturing processes.Another significant development in the history of CAD／CAM followed close behind APT, also developed at MIT, was called the Sketchpad project. With this project, Ivan Sutherland gave birth to the concept of ICG. The Sketchpad project was the first time a computer was used to create and manipulate graphic images on a CRT display in real time. Throughout the remainder of the 1960s and 70s, CAD continued to develop and several vendors made names for themselves by producing and marketing turnkey CAD systems. These were complete systems including hardware，software，maintenance and training sold as a package. These early systems were configured around mainframe and minicomputer. As a result, they were too expensive to achieve wide-scale acceptance by small to medium manufacturing firms.By the late 1970s，it became clear that the microcomputer would eventually play a role in the further development of CAD／CAM. However, early microcomputers did not have the processing power, memory, or graphic capabilities needed for ICG. Consequently, early attempts to configure CAD／CAM systems around a microcomputer failed.In 1983 IBM Introduced the IBM PC，the first microcomputer to have the processing power, memory, and graphic capabilities to be used in CAD／CAM. This led to a rapid increase in the number of CAD／CAM vendors. By l989 the number of CAD/CAM installations based on microcomputers equaled the number based on mainframe and minicomputer.Computer and DesignThe computer has had a major impact on the way everyday tasks associated with design are accomplished. It can be used in many ways to do many things. However, all design tasks accomplished using a computer fall into one of three broad categories:Design modelingDesign analysisDesign reviewIn CAD/CAM design modeling, a geometric model of a product is developed that describes the part mathematically. This mathematical description is converted to graphic form and displayed on a cathode ray tube. The geometric model also allows the graphic image to be easily edited and manipulated once displayed.Design AnalysisThe computer has simplified the design analysis stage of the design process significantly. Once a proposed design has been developed, it is necessary to analyze how it will stand up to the conditions to which it will be subjected. Such analysis methods as heat transfer and stress-strain calculations are time-consuming and complex. With CAD/CAM, special computer programs written specifically for analysis purposes are available.Design ReviewAnother step in the design process that has been simplified by the computer is design review. This involves checking the accuracy of all aspects of the design. There are several ICG capabilities that make design review in CAD/CAM easier than with manual design. CAD-to-CAM InterfaceWith CAD／CAM, the real interface between the design and manufacturing components is the common database they share. This is the essence of CAD／CAM. With manual design and manufacturing, engineers go through each step in the design, drafters produce drawings and other documents to communicate the design, manufacturing personnel use the drawings to develop process plans，and shop personnel actually make the product.With the old approach，until the design and drafting personnel completed their work, the manufacturing personnel did not see it. The design and drafting department did its job and“threw the plans over the wall”to manufacturing so it could do its job. This approach led to continual breakdowns in communication as well as poor relations between the design and manufacturing components. The result was a loss of productivity.With CAD／CAM．manufacturing personnel have access to the data created during the design phase as soon as they are created. At any point in the design process, they can call up information from the design database and use it. Since the data are shared from start to finish, There are no surprises when the completed design is ready to be produced. While designers are creating the database and drafters are documenting the design，manufacturing personnel can be programs.Everything needed by manufacturing personnel to produce the product is contained in the common database. The mathematical models, graphic images，bills of material，parts lists，size，from. locational dimensions, tolerance specifications and material specifications are all contained database计算机辅助设计和计算机辅助（CAD/CAM）纵观人类工业社会的历史，许多发明获得了专利，整个新技术也逐渐形成。

计算机英语词汇
以下是一些计算机相关的英语词汇：
1.CPU：Central Processing Unit，中央处理器
2.RAM：Random Access Memory，随机存取存储器
3.ROM：Read-Only Memory，只读存储器
4.BIOS：Basic Input/Output System，基本输入输出系统
5.OS：Operating System，操作系统
6.GUI：Graphical User Interface，图形用户界面
7.TCP/IP：Transmission Control Protocol/Internet Protocol，传输控制协议/互联网协议
8.HTTP：Hypertext Transfer Protocol，超文本传输协议
9.HTML：Hypertext Markup Language，超文本标记语言
10.DNS：Domain Name System，域名系统
这些词汇是计算机科学和信息技术领域中的基本概念和术语。

通过掌握这些词汇，可以更好地理解和应用计算机技术和网络知识。

计算机外⽂翻译（完整）毕业设计(论⽂)外⽂资料翻译专业：计算机科学与技术姓名：王成明学号：06120186外⽂出处：The History of the Internet附件： 1.外⽂原⽂ 2.外⽂资料翻译译⽂；附件1：外⽂原⽂The History of the InternetThe Beginning - ARPAnetThe Internet started as a project by the US government. The object of the project was to create a means of communications between long distance points, in the event of a nation wide emergency or, more specifically, nuclear war. The project was called ARPAnet, and it is what the Internet started as. Funded specifically for military communication, the engineers responsible for ARPANet had no idea of the possibilities of an "Internet."By definition, an 'Internet' is four or more computers connected by a network.ARPAnet achieved its network by using a protocol called TCP/IP. The basics around this protocol was that if information sent over a network failed to get through on one route, it would find another route to work with, as well as establishing a means for one computer to "talk" to another computer, regardless of whether it was a PC or a Macintosh.By the 80's ARPAnet, just years away from becoming the more well known Internet, had 200 computers. The Defense Department, satisfied with ARPAnets results, decided to fully adopt it into service, and connected many military computers and resources into the network. ARPAnet then had 562 computers on its network. By the year 1984, it had over 1000 computers on its network.In 1986 ARPAnet (supposedly) shut down, but only the organization shut down, and the existing networks still existed between the more than 1000 computers. It shut down due to a failied link up with NSF, who wanted to connect its 5 countywide super computers into ARPAnet.With the funding of NSF, new high speed lines were successfully installed at line speeds of 56k (a normal modem nowadays) through telephone lines in 1988. By that time, there were 28,174 computers on the (by then decided) Internet. In 1989 there were 80,000 computers on it. By 1989, there were290,000.Another network was built to support the incredible number of people joining. It was constructed in 1992.Today - The InternetToday, the Internet has become one of the most important technological advancements in the history of humanity. Everyone wants to get 'on line' to experience the wealth of information of the Internet. Millions of people now use the Internet, and it's predicted that by the year 2003 every single person on the planet will have Internet access. The Internet has truly become a way of life in our time and era, and is evolving so quickly its hard to determine where it will go next, as computer and network technology improve every day.HOW IT WORKS:It's a standard thing. People using the Internet. Shopping, playing games,conversing in virtual Internet environments.The Internet is not a 'thing' itself. The Internet cannot just "crash." It functions the same way as the telephone system, only there is no Internet company that runs the Internet.The Internet is a collection of millioins of computers that are all connected to each other, or have the means to connect to each other. The Internet is just like an office network, only it has millions of computers connected to it.The main thing about how the Internet works is communication. How does a computer in Houston know how to access data on a computer in Tokyo to view a webpage?Internet communication, communication among computers connected to the Internet, is based on a language. This language is called TCP/IP. TCP/IP establishes a language for a computer to access and transmit data over the Internet system.But TCP/IP assumes that there is a physical connecetion between onecomputer and another. This is not usually the case. There would have to be a network wire that went to every computer connected to the Internet, but that would make the Internet impossible to access.The physical connection that is requireed is established by way of modems,phonelines, and other modem cable connections (like cable modems or DSL). Modems on computers read and transmit data over established lines,which could be phonelines or data lines. The actual hard core connections are established among computers called routers.A router is a computer that serves as a traffic controller for information.To explain this better, let's look at how a standard computer might viewa webpage.1. The user's computer dials into an Internet Service Provider (ISP). The ISP might in turn be connected to another ISP, or a straight connection into the Internet backbone.2. The user launches a web browser like Netscape or Internet Explorer and types in an internet location to go to.3. Here's where the tricky part comes in. First, the computer sends data about it's data request to a router. A router is a very high speed powerful computer running special software. The collection of routers in the world make what is called a "backbone," on which all the data on the Internet is transferred. The backbone presently operates at a speed of several gigabytes per-second. Such a speed compared to a normal modem is like comparing the heat of the sun to the heat of an ice-cube.Routers handle data that is going back and forth. A router puts small chunks of data into packages called packets, which function similarly to envelopes. So, when the request for the webpage goes through, it uses TCP/IP protocols to tell the router what to do with the data, where it's going, and overall where the user wants to go.4. The router sends these packets to other routers, eventually leadingto the target computer. It's like whisper down the lane (only the information remains intact).5. When the information reaches the target web server, the webserver then begins to send the web page back. A webserver is the computer where the webpage is stored that is running a program that handles requests for the webpage and sends the webpage to whoever wants to see it.6. The webpage is put in packets, sent through routers, and arrive at the users computer where the user can view the webpage once it is assembled.The packets which contain the data also contain special information that lets routers and other computers know how to reassemble the data in the right order.With millions of web pages, and millions of users, using the Internet is not always easy for a beginning user, especially for someone who is not entirely comfortale with using computers. Below you can find tips tricks and help on how to use main services of the Internet.Before you access webpages, you must have a web browser to actually be able to view the webpages. Most Internet Access Providers provide you with a web browser in the software they usually give to customers; you. The fact that you are viewing this page means that you have a web browser. The top two use browsers are Netscape Communicator and Microsoft Internet Explorer. Netscape can be found at /doc/bedc387343323968011c9268.html and MSIE can be found at /doc/bedc387343323968011c9268.html /ie.The fact that you're reading this right now means that you have a web browser.Next you must be familiar with actually using webpages. A webpage is a collection of hyperlinks, images, text, forms, menus, and multimedia. To "navigate" a webpage, simply click the links it provides or follow it's own instructions (like if it has a form you need to use, it will probably instruct you how to use it). Basically, everything about a webpage is made to be self-explanetory. That is the nature of a webpage, to be easily navigatable."Oh no! a 404 error! 'Cannot find web page?'" is a common remark made by new web-users.Sometimes websites have errors. But an error on a website is not the user's fault, of course.A 404 error means that the page you tried to go to does not exist. This could be because the site is still being constructed and the page hasn't been created yet, or because the site author made a typo in the page. There's nothing much to do about a 404 error except for e-mailing the site administrator (of the page you wanted to go to) an telling him/her about the error.A Javascript error is the result of a programming error in the Javascript code of a website. Not all websites utilize Javascript, but many do. Javascript is different from Java, and most browsers now support Javascript. If you are using an old version of a web browser (Netscape 3.0 for example), you might get Javascript errors because sites utilize Javascript versions that your browser does not support. So, you can try getting a newer version of your web browser.E-mail stands for Electronic Mail, and that's what it is. E-mail enables people to send letters, and even files and pictures to each other.To use e-mail, you must have an e-mail client, which is just like a personal post office, since it retrieves and stores e-mail. Secondly, you must have an e-mail account. Most Internet Service Providers provide free e-mail account(s) for free. Some services offer free e-mail, like Hotmail, and Geocities.After configuring your e-mail client with your POP3 and SMTP server address (your e-mail provider will give you that information), you are ready to receive mail.An attachment is a file sent in a letter. If someone sends you an attachment and you don't know who it is, don't run the file, ever. It could be a virus or some other kind of nasty programs. You can't get a virus justby reading e-mail, you'll have to physically execute some form of program for a virus to strike.A signature is a feature of many e-mail programs. A signature is added to the end of every e-mail you send out. You can put a text graphic, your business information, anything you want.Imagine that a computer on the Internet is an island in the sea. The sea is filled with millions of islands. This is the Internet. Imagine an island communicates with other island by sending ships to other islands and receiving ships. The island has ports to accept and send out ships.A computer on the Internet has access nodes called ports. A port is just a symbolic object that allows the computer to operate on a network (or the Internet). This method is similar to the island/ocean symbolism above.Telnet refers to accessing ports on a server directly with a text connection. Almost every kind of Internet function, like accessing web pages,"chatting," and e-mailing is done over a Telnet connection.Telnetting requires a Telnet client. A telnet program comes with the Windows system, so Windows users can access telnet by typing in "telnet" (without the "'s) in the run dialog. Linux has it built into the command line; telnet. A popular telnet program for Macintosh is NCSA telnet.Any server software (web page daemon, chat daemon) can be accessed via telnet, although they are not usually meant to be accessed in such a manner. For instance, it is possible to connect directly to a mail server and check your mail by interfacing with the e-mail server software, but it's easier to use an e-mail client (of course).There are millions of WebPages that come from all over the world, yet how will you know what the address of a page you want is?Search engines save the day. A search engine is a very large website that allows you to search it's own database of websites. For instance, if you wanted to find a website on dogs, you'd search for "dog" or "dogs" or "dog information." Here are a few search-engines.1. Altavista (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed2. Yahoo (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed Collection3. Excite (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed4. Lycos (/doc/bedc387343323968011c9268.html ) - Web spider & Indexed5. Metasearch (/doc/bedc387343323968011c9268.html ) - Multiple searchA web spider is a program used by search engines that goes from page to page, following any link it can possibly find. This means that a search engine can literally map out as much of the Internet as it's own time and speed allows for.An indexed collection uses hand-added links. For instance, on Yahoo's site. You can click on Computers & the Internet. Then you can click on Hardware. Then you can click on Modems, etc., and along the way through sections, there are sites available which relate to what section you're in.Metasearch searches many search engines at the same time, finding the top choices from about 10 search engines, making searching a lot more effective.Once you are able to use search engines, you can effectively find the pages you want.With the arrival of networking and multi user systems, security has always been on the mind of system developers and system operators. Since the dawn of AT&T and its phone network, hackers have been known by many, hackers who find ways all the time of breaking into systems. It used to not be that big of a problem, since networking was limited to big corporate companies or government computers who could afford the necessary computer security.The biggest problem now-a-days is personal information. Why should you be careful while making purchases via a website? Let's look at how the internet works, quickly.The user is transferring credit card information to a webpage. Looks safe, right? Not necessarily. As the user submits the information, it is being streamed through a series of computers that make up the Internet backbone.The information is in little chunks, in packages called packets. Here's the problem: While the information is being transferred through this big backbone, what is preventing a "hacker" from intercepting this data stream at one of the backbone points?Big-brother is not watching you if you access a web site, but users should be aware of potential threats while transmitting private information. There are methods of enforcing security, like password protection, an most importantly, encryption.Encryption means scrambling data into a code that can only be unscrambled on the "other end." Browser's like Netscape Communicator and Internet Explorer feature encryption support for making on-line transfers. Some encryptions work better than others. The most advanced encryption system is called DES (Data Encryption Standard), and it was adopted by the US Defense Department because it was deemed so difficult to 'crack' that they considered it a security risk if it would fall into another countries hands.A DES uses a single key of information to unlock an entire document. The problem is, there are 75 trillion possible keys to use, so it is a highly difficult system to break. One document was cracked and decoded, but it was a combined effort of14,000 computers networked over the Internet that took a while to do it, so most hackers don't have that many resources available.附件2：外⽂资料翻译译⽂Internet的历史起源——ARPAnetInternet是被美国政府作为⼀项⼯程进⾏开发的。

Introduction to computer1 .Computer LiteracyThe vocabulary of computing is all around you. Before the advent of computers, memory was the mental ability to recall previous experiences; storage was an area where you kept out -of-season clothing; and communication was the act of exchanging opinions and information through writing, speaking, or signs. In today’s world, these words and countless others have taken on new meanings as part of the common terminology used to describe computers and their uses.When you hear the word computer, initially you may think of those found in the workplace—the computers used to create business letters, memos, and other correspondence; calculate payroll; track inventory; or generate invoices. In the course of a day or a week, however, you encounter many other computers. Your home, for instance, may contain a myriad of electronic devices, such as cordless telephones, VCRs, handheld video games cameras, and stereo systems, which include small computers.Computers help you with your banking in the form of automatic teller machines (ATMs) used to deposit or withdraw funds. When you buy groceries, a computer tracks your purchases and calculates the amount of money you owe; and sometimes generates coupons customized to your buying patterns.Even your car is equipped with computers that operate the electrical system, control the temperature, and run sophisticated antitheft devices.Computers are valuable tools. As technology advances and computers extend into every facet of daily living, it is essential you gain some level of computer literacy. To be successful in today’wo4ld, you must have knowledge and understanding of computers and their uses.2. What is a computer and what does it doA computer is an electronic machine, operating under the control of instructions stored in its own memory, which can accept data (input), manipulate the data according to specified rules (process), produce results (output), and store the results for future use.Data is a collection of un-organized facts, which can include words, numbers, images, and sounds. Computers manipulate and process data to create information.Information is data that is organized, has meaning, and is useful. Examples are reports, newsletters, a receipt, a picture, an invoice, or a check. Data is processed and manipulated to create a check.Data entered into a computer is called input. The processed results are called output. Thus, a computer processes input to create output. A computer also can hold data and information for future use in an area called storage. This cycle of input, process, output, and storage is called the information processing cycle.A person that communicates with a computer with a computer or uses the information it generates is called a user. The electric, electronic, and mechanical equipment that makes up a computer is called hardware. Software is the series of instruction that tells the hardware how to perform tasks. Without software, hardware is useless; hardware needs the instructions provided by software to process data into information.3.The components of a computerA computer consists of a variety of hardware components that work together with software to perform calculations, organize data, and communicate with other computer.These hardware components include input devices, output devices, a system unit, storage devices, and communications devices.3.1 Input DevicesAn input device allows a user to enter data and commands into the memory of a computer. Four commonly used input devices are the keyboard, the mouse, a microphone, and a PC camera.A computer keyboard contains keys that allow you to type letters of the alphabet, number, spaces, punctuation marks, and other symbols. A computer keyboard also contains special keys that allow you to allows you to move the pointer. You also can make choices and initiate processing on the computer by using a mouse.A microphone allows you to speak to the computer in order to enter data and control the actions of the computer. A PC camera allows others to see you wh ile communicating with you, as well as allowing you to edit videos, create a movie, and take digital photographs.3.2 Output DevicesA printer produces text and graphics, such as photographs, on paper or other hardcopy medium. A monitor, which looks like a television screen, is used todisplay text and graphics. Speakers allow you to hear music, voice, and other sounds generated by the computer.3.3 System UnitThe system unit is a box-like case made of metal or plastic that houses the computer electronic circuitry. The circuitry in the system unit usually is part of or is connected to a circuit board called the motherboard.Two main components on the motherboard are the central processing unit (CPU), also called a processor, is the electronic device that interprets and carries out the instructions that operate the computer.Memory is a series of electronic elements that temporarily holds data and instructions while they are being processed by the CPU. Both the processor and memory are chips. A chip is an electronic device that contains many microscopic pathways designed o carry electrical current. Chips(Figure1-2), which usually are no bigger than one-half inch square, are packaged so they can be connected to a motherboard or other circuit boards.Some computer components, such as the processor and memory resided inside the system unit; that is, they are internal. Other components, like keyboard, mouse, microphone, monitor, PC camera, and printer, are often system unit. These devices are considered external. Any external device that attaches to the system unit is called a peripheral device.3.4 Storage DevicesStorage holds data, instructions, and information for future use. Storage differs from memory, which can hold these items permanently, whereas memory holds these items only temporarily while they are being processed. A storage medium (media is the plural) is the physical material on which data, instructions, and information are stored. One commonly used storage medium is a disk, which is a round, flat piece of plastic or metal on which items can be encoded, or written.A storage device is used to record and retrieve data, instructions,, and information to and from a storage medium. Storage devices often function as a source of input because they transfer items from storage into memory. Four common storage devices are a floppy disk drive, a hard disk drive, a CD-ROM drive, and a DVD-ROM drive. A disk drive is a device that reads from and writes onto a disk.A floppy disk consists of a thin, circular, flexible disk enclosed in a plastic shell. A floppy disk stores data, instructions, and information using magneticpatterns and can be inserted into and removed from a floppy disk drive. A ZIP DISK give is a higher capacity floppy disk that can store the equival ent of about 70standard floppy disks.A hard disk provides much greater storage capacity than a floppy disk. A hard disk usually consists of several circular disks on which data, instructions, and information are stored magnetically. These disks are enclosed in an airtight, sealed case, which often is housed inside the system unit. Some hard disks are removable, which means they can be inserted and removed from a hard disk drive, much like a floppy disk. Removable disks are enclosed in plastic or metal cartridges so that they can be removed from the drive. The advantage of removable media such as a floppy disk and removable hard disk is it can be taken out of the computer and transporter or secured.Another type of disk used to store data is the compact disc. A compact disc stores data using microscopic pits, which are created or played using a CD-ROM drive, which is accessed or played using a CD-ROM drive. A variation of the standard CD-ROM, you can also erase and store data on a CD-RW. A newer type of compact disc is a FVD-ROM, which has tremendous storage capacities enough for a full-length movie. To use a DVD-ROM, you need a DVD-ROM drive.3.5 Communications DevicesCommunication devices enable computer users to communicate and to exchange items such as data, instruction, and information with another computer. Communication devices transmit these items over transmission media, such as cable, telephone lines, or other means, used to establish a connection between two computers. A modem is a communication device that enables computers to communicate via telephone lines or other means. Although modems are available as both external and internal devices, most are internal; that is, contained within the system unit.4. Why is a computer a powerful toolA computer’s power is derived from its capability of performing the information processing cycle operations with speed, reliability, and accuracy; its capacity to store huge amounts of data, instructions, and information; and its ability to communicate with other computers.4.1 SpeedInside the system unit, operation occurs through electronic circuits. When data, instructions, and information, flow along these circuits, they travel at closeto the speed of light. This allows billions of operations to be carried out i n a single second.4.2 ReliabilityThe electronic components in modern computers are dependable because they have a low failure rate. The high reliability of components enables the computer to produce consistent results.4.3 AccuracyComputers can process large amounts of data and generate error-free results, provided the data is entered correctly. If inaccurate data is entered, the resulting output will be incorrect. This computing principle known as garbage in, garbage out (GIGO), points out that the accu racy of a computer’s output depends on the accuracy of the input.4.4 StorageMany computers can store enormous amounts of data and make this data available for processing any time it is needed. Using current storage devices, the data can be transferred quickly from storage to memory, processed, and then stored again for future use.4.5 CommunicationsMost computers today have the capability of communicating with other computers. Computers with this capability can share any of the four information processing cycle operations—input, process, output, and storage—with another computer. For example, two computers connected by a communications device such as a modem can share stored data, instructions, and information. When two or more computers are connected together via communications media and devices, they comprise a network is the Internet, a worldwide collection of networks that links together millions of businesses, government installations, educational institutions, and individuals.5. Computer SoftwareSoftware, also called a computer program or simply a program, is a series of instructions that tells the hardware of a computer what to do. For example, some instructions direct the computer to allow you to input data from the keyboard and store it in memory. Other instructions cause data stored in memory to be used in calculations such as adding a series of numbers to obtain a total. Some instructions compare two values stored in memory and direct the computer to perform alternativeOperations based on the results of the comparison; and some instructions direct the computer to print a report, display information on the monitor, draw a color graph on the monitor, or store information on a disk.Before a computer can perform, or execute, a program, the instructions in the program must be placed, or loaded, into the memory of the computer. Usually, they are loaded into memory from storage. For example, a program might be loaded from the hard disk of a computer into memory for execution.When you purchase a program, such as one that contains legal documents, you will receive one or more floppy disks, one or more CD-ROMs, or a single DVD-ROM on which the software is stored. To use this software, you may install the software on the computer’s hard disk.Software is the key to productive use of computers. With the correct software, a computer can become a valuable tool. Software can be categorized into two types: system software and application software. The following sections describe these categories of software.计算机引论1.计算机文化计算词汇无处不在。

中文翻译：1 什么是 FlashFlash 是一种创作工具，设计人员和开发人员可使用它来创建演示文稿、应用程序和其它允许用户交互的内容。

Flash 可以包含简单的动画、视频内容、复杂演示文稿和应用程序以及介于它们之间的任何内容。

通常，使用 Flash 创作的各个内容单元称为应用程序，即使它们可能只是很简单的动画。

您可以通过添加图片、声音、视频和特殊效果，构建包含丰富媒体的 Flash 应用程序。

Flash 特别适用于创建通过 Internet 提供的内容，因为它的文件非常小。

Flash 是通过广泛使用矢量图形做到这一点的。

与位图图形相比，矢量图形需要的内存和存储空间小很多，因为它们是以数学公式而不是大型数据集来表示的。

位图图形之所以更大，是因为图像中的每个像素都需要一组单独的数据来表示。

要在 Flash 中构建应用程序，可以使用 Flash 绘图工具创建图形，并将其它媒体元素导入 Flash 文档。

接下来，定义如何以及何时使用各个元素来创建设想中的应用程序。

在 Flash 中创作内容时，需要在 Flash 文档文件中工作。

Flash 文档的文件扩展名为 .fla (FLA)。

Flash 文档有四个主要部分：舞台是在回放过程中显示图形、视频、按钮等内容的位置。

时间轴用来通知 Flash 显示图形和其它项目元素的时间，也可以使用时间轴指定舞台上各图形的分层顺序。

位于较高图层中的图形显示在较低图层中的图形的上方。

库面板是 Flash 显示 Flash 文档中的媒体元素列表的位置。

ActionScript代码可用来向文档中的媒体元素添加交互式内容。

例如，可以添加代码以便用户在单击某按钮时显示一幅新图像，还可以使用 ActionScript 向应用程序添加逻辑。

逻辑使应用程序能够根据用户的操作和其它情况采取不同的工作方式。

Flash 包括两个版本的 ActionScript，可满足创作者的不同具体需要。

有关编写 ActionScript 的详细信息，请参阅"帮助"面板中的"学习 Flash 中的 ActionScript 2.0"。

译文Apache Struts 2“Apache Struts 2 is an elegant, extensible framework for creating enterprise-ready Java web applications. The framework is designed to streamline the full development cycle, from building, to deploying, to maintaining applications over time” -The Apache Software Foundation.4.1简介Struts是Apache的一个应用于Java Web的网络编程的开源框架。

Struts框架的创造者和发起者是McClanahan。

后来在2002年，Struts框架由Apache软件基金会收购和接管。

Struts 提供给程序员一个易于组织基于JSP和Servlet的HTML格式和Java代码的框架。

Struts1几乎能与所有标准的Java技术和Jakarta配置包协同工作。

然而,随着需求的不断增长，Struts1在网络应用程序暴露出来许多问题,所以为了满足需求，导致Strut2推出,Strut2能更好地为开发者提供服务,如 Ajax、高效开发和可扩展性。

4.1.1 Struts 2的起源自从2000年Apache Struts的发起,Struts框架取得了非常大的成功,被大多数标准所接纳,得到了很大的发展,如果不是这样,哪里会有今天java web程序的成绩。

它的历史,告诉我们Struts是怎样组织JSP和/ Servlets，而提供了固定的框架。

Struts融入server-generated HTML与Javascript,客户端验证,也使得开发比较容易和维护。

随着时间推进的和客户对web 需求扩大,网站应用程序取得硕果累累,Struts1太老了，开始在越来越多的网站前端开发者视野中淡去。

计算机类毕业外文翻译The Phase to Develop the systemWith the society's development, the personal relationship is day by day intense. How enhances the personal relationship, reduces the management cost, the enhancement service level and pensonal competitive ability, is every one superintendent most matter of concern. More and more superintendents thought the implementation computer scientific style management solves this question.Management information systems (MIS), are information systems, typically computer based, that are used within an organization. World net described an information system as‖ a system consisting of the network of all communication channels used with an organization‖.Generally speaking, MIS involved the following parts:1 Conduct a Preliminary Investigation（1）What is the objective of the first phase of the SDLC?Attention: SDLC means Systems Development Life Cycle.The objectives of phase 1, preliminary investigation, are to conduct a preliminary analysis, propose alternative solutions, describe the costs and benefits of each solution, and submit a preliminary plan with recommendations. The problems are briefly identified and a few solutions are suggested. This phase is often called a feasibility study.（2）Conduct the preliminary analysisIn this step, you need to find out what the organization’s objectives are and to explore the nature and scope of the problems under study.Determine the organization’s objectives: Even if a problem pertains to only a small segment of the organization, you cannot study it in isolation. You need to find out what the overall objectives of the organization are and how groups and departments with in the organization interact. Then you need to examine the problem in that context.Determine the nature and scope of the problems: you may already have a sense of the nature and scope of a problem. However, with a fuller understanding of the goals of the organization, you can now take a closer look at the specifics. Is too much time being wasted on paperwork? On waiting for materials? On nonessential tasks? How pervasive is the problem within the organization? Outside of it? What people are most affected? And so on. Your reading and your interviews should give you a sense of the character of the problem.（3）Propose alternative solutionsIn delving into the organization’s objectives and the specific problems, you may have already discovered some solutions. Other possible solutions may be generated by interviewing people inside the organization, clients or customers, suppliers, and consultants and by studying what competitors are doing. With this data, you then have three choices. You can leave the system as is, improve it, or develop a new system.Leave the system as is: often, especially with paper-based or no technological systems, the problem really isn’t bad enough to justify the measures and expenditures required to get rid of it.Improve the system: sometimes changing a few key elements in the system upgrading to a new computer or new software, or doing a bit of employee retraining, for example will do the trick. Modifications might be introduced over several months, if the problem is no serious.Develop a new system: if the existing system is truly harmful to the organization, radical changes may be warranted. A new system would not mean just tinkering around the edges or introducing some new piece of hardware or software. It could mean changes in every part and at every level.（4）Describe costs and benefitsWhichever of the three alternatives is chose, it will have costs and benefits. In this step, you need to indicate what these are.The changes or absence of changes will have a price tag, of course, and you need to indicate what it is. Greater costs may result in greater benefits, which, in turn, may offer savings. The benefits may be both tangible—such as costly savings –and intangible—such as worker satisfaction. A process may be speeded up, streamlined through the elimination of unnecessary steps, or combined with other processes. Input errors or redundant output may be reduced. Systems and subsystems may be better integrated. Users may be happier with the system. Customers or suppliers may interact more efficiently with the system. Security may be improved. Costs may be cut.（5）Submit a preliminary planNow you need to wrap up all your findings in a written report, submitted to the executives(probably top managers) who are in a position to decide in which direction to proceed—make no changes, change a little, or change a lot—and how much money to allow the project. You should describe the potential solutions, costs, and benefits and indicate your recommendations. If management approves the feasibility study, then the systems analysis phase can begin.2 Do a Detailed Analysis of the System（1）What tools are used in the second phase of the SDLC to analyze data?The objectives of phase 2, systems analysis, are to gather data, analyze the data, and write a report. The present system is studied in depth, and new requirements are specified. Systems analysis describes what a system is already doing and what it should do to meet the needs of users. Systems design—the next phase—specifies how the system will accommodate the objective.In this second phase of the SDLC, you will follow the course prescribed by management on the basis of your phase/feasibility report. We are assuming what you have been directed to perform phase 2—to do a careful analysis of the existing system, in order to understand how the new system you propose would differ. This analysis will also consider how people’s positions and tasks will have to change if the new system is put into effect. In general, it involves a detailed study of: The information needs of the organization and all users;The actives, resources, and products or any present information systems;The information systems capabilities required to need the established information needs and user needs.（2）Gather dataIn gathering data, systems analysts use a handful of tools. Most of them not tem ply technical. They include written documents, interviews, questionnaires, observation, and sampling.Written documents: a great deal of what you need is probably available in the form of written documents, and so on. Documents are a good place to start because they tell you how things are or are supposed to be. These tools will also provide leads on people and areas to pursuer further.Interviews: interviews with managers, workers, clients, suppliers, and competitors will also give you insights. Interviews may be structured or unstructured.Questionnaires: questionnaires are useful for getting information for large groups of people when you can’t get around to interviewing everyone. Questionnaires may also yield more information if respondents can be anonymous. In addition, this tool is convenient, is inexpensive, and yields a lot of data. However, people may not return their forms, results can be ambiguous, and with anonymous questionnaires you’ll have no opportunity to follow up.Observation: no doubt you’ve sat in a coffee shop or on a park bench and just alone ―a person is watching‖. This can be a tool for analysis, too. Through observation you can see how people interact with one another and how paper moves through an organization. Observation can be non-participant or participant. If you are a non-participant observer, and people knew they are a participant observer, you may gain more insights by experiencing the conflicts and responsibilities of the people you are working with.（3）Analyze the dataOnce the data is gathered, you need to come to grips with it and analyze it. Many analytical tools, or modeling tools, are available. Modeling tools enables a systems analyst to present graphic representations of a system. Examples are CASE tools,data flow diagrams, systems flow charts, connectivity diagrams, grid charts, decision tables, and object-oriented analysis.For example, in analyzing the current system and preparing data flow diagrams, the systems analyst must also prepare a data dictionary, which is then used and expanded during all remaining phases of the SDLC. A data dictionary defines all the elements that make up the data flow. Among other things, it records what each data element is by name, how long it is, are where it is used, as well as any numerical values assigned to it. This information is usually entered into a data dictionary software program.The Phase: Design the System（4）At the conclusions of the third phase of the SDLC, what should have been created?The objectives of phase 3, systems design, are to do a preliminary design and then a detail and to write a report. In this third phase of the SDLC, you will essentially create a rough draft and then a detail draft of the proposed information system.（5）Do a preliminary designA preliminary design describes the general foundational capabilities of proposed information system. It reviews the system requirements and then considers major components of the system. Usually several alternative systems are considered, and the costs and the benefits of each are evaluated.Some tools that may be used in the preliminary design an the detail design are following:CASE tools: they are software programs that automate various activities of the SDLC in several phases. This screen is from one of their banking system tools. It shows a model for an A TM transaction. The purchaser of the CASE tool would enter details relative to the particular situation. This technology is intended to speed up to the process of developing systems and to improve the quality of the resulting systems.Project management software: it consists of programs used to plan, schedule, a control the people, costs, and resources required to complete a project on time.3 A detail designA detail design describes how a proposed information system will deliver the general capabilities in the preliminary design. The detail design usually considers the following parts of the system, in this order: output requirements, and system controls and backup.(1) Output requirements: the first thing to determine is what you want the system to produce. In this first step, the systems analyst determines what media the appearance or format of the output, such as headings, columns, and menus.(2) Input requirements: once you know the output, you can determine the inputs, here, too, you must define the type of input, such as keyboard or source data entry. You must determine in what form data will be input and how it will be checked for accuracy. You also need to figure out what volume of data the system can be allowed to take in.(3) Storage requirements: using the data dictionary as a quite, you need to define the files and databases in the information system. How will the files be organized? What kind of storage devices will be used? How will they interface with other storage devices inside and outside of the organization? What will be the volume of database activity?(4) Processing and networking requirements, what kind of computer or computers will be used to handle the processing? What kind of operating system and applications software will be used? Will the computer or computers be tied to others in a network? Exactly what operations will be performed on the input data to achieve the desired output information? What kinds of user interface are desired?(5) System controls backup: finally, you need to think about matters of security, privacy, and data accuracy. You need to prevent unauthorized users from breaking into the system, for example, and snooping in private files. You need to devise auditing procedures and to set up specifications for testing the new system. Finally, you need to institute automatic ways of backing up information and storing it else where in case the system fails or is destroyed.4 Develop/Acquire the System（1）What general tasks do systems analysts perform in the fourth phase of the SDLC?Systems development/acquisition, the systems analysts or others in the organization acquire the software, acquire thehardware, and then test the system. This phase begins once management has accepted the report containing the design and has‖green lighted‖the way to development. Depending on the size of the project, this phase will probably involve substantial expenditures of money and time. However, at the end you should have a workable system.（2）Acquire softwareDuring the design stage, the systems analyst may have had to address what is called the ―make-or-buy‖ decision; if not, that decision certainly cannot be avoided now. In the make-or-buy decision, you decide whether you have to create a program –have it custom-written—or buy it. Sometimes programmers decide they can buy an existing software package and modify it rather than write it from scratch.If you decide to create a new program, then the question is whether to use the organization’s own staff programmers or to hair outside contract programmers. Whichever way you go, the task could take months.（3）Acquire hardwareOnce the software has been chosen, the hardware to run it must be acquired or upgraded. It’s possible you will not need to obtain any new hardware. It’s also possible that the new hardware will cost millions of dollars and involve many items: models, and many other devices. The organization may prefer to lease rather than buy some equipment, especially since chip capability was traditionally doubled about every 18 months.（4）Test the systemWith the software and hardware acquired, you can now start testing the system in two stages: first unit testing and then system testing. If CASE tools have been used throughout the SDLC, testing is minimized because any automatically generated program code is more likely to be error free.5 Implement the System（1）What tasks are typically performed in the fifth phase of the SDLC?Whether the new information system involves a few handheld computers, and elaborate telecommunications network, or expensive mainframes, phase 5,systems implementation, with involve some close coordination to make the system not just workable but successful, and people are tainted to use it.6 Maintain the System（1）What two tools are often used in the maintenance phase of the SDLC?Phase 6, systems maintain, adjusts and improves the system by having system audits and periodic evaluations and by making changes based on new conditions.Even with the conversion accomplished and the users trained, the system won’t just run itself. There is a sixth-and never-ending –phase in which the information system must—monitored to ensure that it is effective. Maintenance includes not only keeping the machinery running but also updating and upgrading the system to keep pace with new products, services, customers, government regulations, and other requirements.附件二英汉翻译系统开发阶段随着社会的发展，个人关系管理在日常生活中起的左右显而易见，怎样增强个人管理管理能力，减少管理成本，加强服务水平和个人的竞争力是困扰每一个主管的重要问题之一。

计算机专业外文翻译毕业设计英文翻译作者：XXXThe Delphi Programming LanguageThe Delphi development environment is based on an object-oriented extension of thePascal programming language known as Object Pascal. Most modern programming languagessupport object-oriented programming (OOP). OOP languages are based on three fundamentalconcepts: encapsulation (usually implemented with classes), inheritance, and polymorphism(or late binding).1Classes and ObjectsDelphi is based on OOP concepts, and in particular on the definition of new class types.The use of OOP is partially enforced by the visual development environment, because forevery new form defined at design time, Delphi automatically defines a new class. In addition,every component visually placed on a form is an object of a class type available in or added tothe system library.As in most other modern OOP languages (including Java and C#), in Delphi a class-typevariable doesn't provide the storage for the object, but is only a pointer or reference to theobject in memory. Before you use the object, you must allocate memory for it by creating anew instance or by assigning an existing instance to the variable: varObj1, Obj2: TMyClass;begin // assign a newly created objectObj1 := TMyClass.Create; // assign to an existing objectObj2 := ExistingObject;The call to Create invokes a default constructor available for every class, unless the classredefines it (as described later). To declare a new class data type in Delphi, with some localdata fields and some methods, use the following syntax:typeTDate = classMonth, Day, Year: Integer;procedure SetValue (m, d, y: Integer);function LeapYear: Boolean;第 1 页共 13 页毕业设计英文翻译作者：XXXend;2Creating Components DynamicallyTo emphasize the fact that Delphi components aren't much different from other objects(and also to demonstrate the use of the Self keyword), I've written the CreateComps example.This program has a form with no components and a handler for its OnMouseDown event,which I've chosen because it receives as a parameter the position of the mouse click (unlikethe OnClick event). I need this information to create a button component in that position. Hereis the method's code:procedure TForm1.FormMouseDown (Sender: TObject;Button: TMouseButton; Shift: TShiftState; X, Y: Integer);Var Btn: TButton;beginBtn := TButton.Create (Self);Btn.Parent := Self;Btn.Left := X;Btn.Top := Y;Btn.Width := Btn.Width + 50;Btn.Caption := Format ('Button at %d, %d', [X, Y]);end;The effect of this code is to create buttons at mouse-click positions, as you can see in thefollowing figure. In the code, notice in particular the use of the Self keyword as both theparameter of the Create method (to specify the component's owner) and the value of theParent property.（The output of theexample,which creates Button components at run time第 2 页共 13 页毕业设计英文翻译作者：XXX3EncapsulationThe concept of encapsulation is often indicated by the idea of a "black box." You don'tknow about the internals: You only know how to interface with the black box or use itregardless of its internal structure. The "how to use" portion,called the class interface, allowsother parts of a program to access and use the objects of that class. However, when you usethe objects, most of their code is hidden. You seldom know what internal data the object has,and you usually have no way to access the data directly. Of course, you are supposed to usemethods to access the data, which is shielded from unauthorized access. This is theobject-oriented approach to a classical programming concept known as information hiding.However, in Delphi there is the extra level of hiding, through properties,4PrivateProtectedand PublicFor class-based encapsulation, the Delphi language has three access specifiers: private,protected, and public. A fourth, published, controls run-time type information (RTTI) anddesign-time information, but it gives the same programmatic accessibility as public. Here arethe three classic access specifiers:, The private directive denotes fields and methods of a class thatare not accessible outsidethe unit that declares the class., The protected directive is used to indicate methods and fields with limited visibility. Onlythe current class and its inherited classes can access protected elements. More precisely,only the class, subclasses, and any code in the same unit as the class can access protectedmembers。

毕业设计（论文）文献翻译英文资料：Computer Networks and DatabaseworksSome reasons are causing centralized computer systems to give way to networks.The first one is that many organizations already have a substantial number of computers in operation ,often located far apart .Initially ,each of these computers may have worked in isolation from the other ones ,but at a certain time ,management may have decided to connect them to be able to correlate information about the entire organization .Generally speaking ,this goal is to make all programs ,data ,and other resources available to anyone on the network without regard to the physical location of the resource and the user .The second one is to provide high reliability by having alternative sources of supply .With a network ,the temporary loss of a single computer is much less serious ,because its users can often be accommodated elsewhere until the service is restored .Yet another reason of setting up a computer network is computer network can provide a powerful communication medium among widely separated people .Application of NetworksOne of the main areas of potential network sue is access to remote database .It may someday be easy for people sitting at their terminals at home to make reservations for airplanes trains , buses , boats , restaurants ,theaters ,hotels ,and so on ,at anywhere in the world with instant confirmation .Home banking ,automated newspaper and fully automated library also fall in this category .Computer aided education is another possible field for using network ,with many different courses being offered.Teleconferencing is a whole new form communication. With it widely separated people can conduct a meeting by typing messages at their terminals .Attendees may leave at will and find out what they missed when they come back .International contacts by human begin may be greatly enhanced by network based communication facilities .Network StructureBroadly speaking,there are two general types of designs for the communication subnet:(1)Point –to –point channels(2)Broadcast channelsIn the first one ,the network contains numerous cables or lesased telephone lines ,each one connecting a pair of nodes .If two nodes that do not share a cablewish to communicate ,they must do this indirectly via other nodes .When a message is sent from node to another via one or more inter mediate modes ,each intermediate node will receive the message and store it until the required output line is free so that it can transmit the message forward .The subnet using this principle is called a point –to –piont or store –and –forward subnet .When a point –to –point subnet is used ,the important problem is how to design the connected topology between the nodes .The second kind of communication architecture uses broadcasting.In this design there is a single communication channel shared by all nodes .The inherence in broadcast systems is that messages sent by any node are received by all other nodes .The ISO Reference ModelThe Reference Model of Open System Interconnection (OSI),as OSI calls it ,has seven layers .The major ones of the principles ,from which OSI applied to get the seven layers ,are as follows:(1)A layer should be created where a different level of abstraction is needed.(2)Each layer should perform a well defined function .(3)The function of each layer should be chosen with an eye toward defininginternationally standardized protocols.(4)The layer boundaries should be chosen to minimize the information flow acrossthe interfaces .(5)The number of layers should be large enough so that distinct need not be puttogether in the same layer without necessity ,and small enough so that the architecture will not become out control .The Physical LayerThe physical layer is concerned with transmitting raw bits over a communication channel .Typical questions here are how many volts shoule be used to represent an 1 and how many a 0,how many microseconds a bit occupies ,whether transmission may proceed simultaneously in both are finished ,how to establish the initial connection and what kind of function each pin has .The design issues here largely deal with mechanical ,electrical and procedural interfacing to the subnet .The data link layerThe task of the data link layer is to obtain a raw transmission facility and to transform it into a line that appears free of transmission errors to the network layer .It accomplishes this task by breading the input data up into dataframes ,transmitting the frames sequentially ,and processing the acknowledgment frames sent back the receiver .Since the physical layer merely accepts and transmits a stream of bits without any regard to meaning or structure ,it can create and recognize frame boundaries until the data link layer .This can be accomplished by attaching special bits patterns to the beginning and the end of the frame .But it produce two problems :one is a noise burst on the line can destroy a frame completely .In this case ,the software in the source machine must retransmit the frame .The other is that some mechanismmust be employed to let the transmitter know how much buffer space the receiver has at the moment .The network layerThe network layer controls the operation of subnet .It determines the chief characteristics of the node-host interface ,and how packets ,the units of information exchanged in this layer ,are routed within the subnet .What this layer if software does ,basically ,is to accept messages from the source host ,convert them to packets ,and observe the packets to get the destination .The key design issue is how the route is determined .It could not only base on static table ,either are “wired into”the network and rarely changed ,by also adopt highly dynamic manner ,which can determine packet again to reflect the current network load .The transport layerThe basic function of transport layer is to accept data from the session layer ,split it up into smaller units ,if necessary ,pass these to the network layer ,and ensure that the pieces all arrive correctly at the other end .This layer is a true end-to-end layer .In other words ,a program on the source machine carries on a convene station with as similar program on the destination machine , using the message header and control messages .The session layerWith the session layer , the user must negotiate to establish a connection with a process on another machine .The connection is usually called a session. A session might be used to allow a user to log into a remote time-sharing system or to transfer a file between two machines .The operation of setting up a session between two processes is often called binding .Another function of the session layer is to manage the session once it has been setup .The presentation layerThe presentation layer could be designed to accept ASCⅡstrings as input and produce compressed bit patterns as output .This function of the presentation layer is called text compression .In addition ,this layer can also perform other trans formations .Encryption provide security is one possibility .Conversion between character codes ,such as ASCⅡto EBCDIC,might often be useful .More generally ,different computers usually have incompatible file formats ,so a file conversion option might be useful at times .The application layerMany issues occur here .For example ,all the issues of network transparency ,hiding the physical distribution of resources from user .Another issue is problem partitioning :how to divide the problem among the various machine in order to take maximum advantage of the network .2.Database systemThe conception used for describing files and databases has varied substantially in the same organization .A database may be defined as a collection of interrelated data stored together with as little redundancy as possible to serve one or more applications in an optimal fashion ;the data are stored so that they are independent of programs which use the data ;a common and retrieving existing data within the databases if they are entirely separate in structure .A database may be designed for batch processing ,real-time processing ,or in-line processing .A database system involve application program ,DBMS ,and database.One of the most important characteristics of most databases is that they will constantly need to change and grow .Easy restructuring of the database must be possible as new data types and new applications are added .The restructuring should be possible without having to rewrite the ap0plication program and in general should cause as little upheaval as possible .The ease with which a database can be changed will have a major effect on the rate at which data-processing can be developed in a corporation .The tem data independence is often quoted as being one of the main attributes of a data base .It implies that the data and the application programs which use them are independent so that either may be changed without changing the other .When a single set of data items serves a variety of applications ,different application programs perceive different relationships between the data items .To a large extent ,data-base organization is concerned with the representation between the data item about which we store information referred to as entities .An entity may be a tangible object or nontangible .It has various properties which we may wish to record .It can describes the real world .The data item represents an attribute ,and the attribute must be associated with the relevant entity .We design values to the attributes ,one attribute has a special significance in that it identifies the entity .An attribute or set of attributes which the computer uses to identify a record or tuple is referred to as a key .The primary key is defined as that key used to uniquely identify one record or tuple .The entity identifier consisting of one or more attributes .The primary key is of great importance because it is used by the computer in locating the record or tuple by means of an index or addressing algorithm .If the function of a data base were merely to store data ,its organization would be simple .Most of the complexities arise from the fact that is must also show the relationships between the various items of data that are stored .It is different to describe the data in logical or physical .The logical data base description is referred to as a schema .A schema is a chart of the types of data that one used .It gives the entities and attributes ,and specifics the relations between them .It is formwork into which the values of the data-items can be fitted .We must distinguish between a record type and a instance of the record .When we talk about a “personnel record”,this is really a record typed .There are no data vales associated with it .The term schema is used to mean an overall chart of all of the data-types and record types stored in a data base .The term subschema refers to an application programmer’s view of the data he uses .Many different sub schemas can be derived from one schema .The schema and the subschema are both used by the data-base management system ,the primary function of which is to serve the application programs by executing their data operations .A DBMS will usually be handing multiple data calls concurrently .It must organize its system buffers so that different data operations can be in process together .It provides a data definition language to specify the conceptual schema and most likely ,some of the details regarding the implementation of the conceptual schema by the physical schema .The data definition language is a high-level language ,enabling one to describe the conceptual schema in terms of a “data model”.The choice of a data model is a difficult one ,since it must be rich enough in structure to describe significant aspects of the real world ,yet it must be possible to determine fairly automatically an efficient implementation of the conceptual schema by a physical schema .It should be emphasized that while a DBMS might be used to build small data bases ,many data bases involve millions of bytes ,and an inefficient implementation can be disastrous .We will discuss the data model in the following and the .NET Framework is part of Microsoft's overall .NET framework, which contains a vast set of programming classes designed to satisfy any conceivable programming need. In the following two sections, you learn how fits within the .NET framework, and you learn about the languages you can use in your pages.The .NET Framework Class LibraryImagine that you are Microsoft. Imagine that you have to support multiple programming languages—such as Visual Basic, JScript, and C++. A great deal of the functionality of these programming languages overlaps. For example, for each language, you would have to include methods for accessing the file system, working with databases, and manipulating strings.Furthermore, these languages contain similar programming constructs. Every language, for example, can represent loops and conditionals. Even though the syntax of a conditional written in Visual Basic differs from the syntax of a conditional written in C++, the programming function is the same.Finally, most programming languages have similar variable data types. In most languages, you have some means of representing strings and integers, for example. The maximum and minimum size of an integer might depend on the language, but the basic data type is the same.Maintaining all this functionality for multiple languages requires a lot of work. Why keep reinventing the wheel? Wouldn't it be easier to create all this functionality once and use it for every language?The .NET Framework Class Library does exactly that. It consists of a vast set of classes designed to satisfy any conceivable programming need. For example, the .NET framework contains classes for handling database access, working with the file system, manipulating text, and generating graphics. In addition, it contains more specialized classes for performing tasks such as working with regular expressions and handling network protocols.The .NET framework, furthermore, contains classes that represent all the basic variable data types such as strings, integers, bytes, characters, and arrays.Most importantly, for purposes of this book, the .NET Framework Class Library contains classes for building pages. You need to understand, however, that you can access any of the .NET framework classes when you are building your pages.Understanding NamespacesAs you might guess, the .NET framework is huge. It contains thousands of classes (over 3,400). Fortunately, the classes are not simply jumbled together. The classes of the .NET framework are organized into a hierarchy of namespaces.ASP Classic NoteIn previous versions of Active Server Pages, you had access to only five standard classes (the Response, Request, Session, Application, and Server objects). , in contrast, provides you with access to over 3,400 classes!A namespace is a logical grouping of classes. For example, all the classes that relate to working with the file system are gathered together into the System.IO namespace.The namespaces are organized into a hierarchy (a logical tree). At the root of the tree is the System namespace. This namespace contains all the classes for the base data types, such as strings and arrays. It also contains classes for working with random numbers and dates and times.You can uniquely identify any class in the .NET framework by using the full namespace of the class. For example, to uniquely refer to the class that represents a file system file (the File class), you would use the following:System.IO.FileSystem.IO refers to the namespace, and File refers to the particular class. NOTEYou can view all the namespaces of the standard classes in the .NET Framework Class Library by viewing the Reference Documentation for the .NET Framework. Standard NamespacesThe classes contained in a select number of namespaces are available in your pages by default. (You must explicitly import other namespaces.) These default namespaces contain classes that you use most often in your applications:•System—Contains all the base data types and other useful classes such as those related to generating random numbers and working with dates and times. •System.Collections— Contains classes for working with standard collection types such as hash tables, and array lists.•System.Collections.Specialized— Contains classes that represent specialized collections such as linked lists and string collections.•System.Configuration— Contains classes for working with configuration files (Web.config files).•System.Text— Contains classes for encoding, decoding, and manipulating the contents of strings.•System.Text.RegularExpressions— Contains classes for performing regular expression match and replace operations.•System.Web— Contains the basic classes for working with the World Wide Web, including classes for representing browser requests and server responses. •System.Web.Caching—Contains classes used for caching the content of pages and classes for performing custom caching operations.•System.Web.Security— Contains classes for implementing authentication and authorization such as Forms and Passport authentication.•System.Web.SessionState— Contains classes for implementing session state. •System.Web.UI—Contains the basic classes used in building the user interface of pages.•System.Web.UI.HTMLControls— Contains the classes for the HTML controls. •System.Web.UI.WebControls— Contains the classes for the Web controls..NET Framework-Compatible LanguagesFor purposes of this book, you will write the application logic for your pages using Visual Basic as your programming language. It is the default language for pages (and the most popular programming language in the world). Although you stick to Visual Basic in this book, you also need to understand that you can create pages by using any language that supports the .NET Common Language Runtime. Out of the box, this includes C# (pronounced See Sharp), (the .NET version of JavaScript), and the Managed Extensions to C++.NOTEThe CD included with this book contains C# versions of all the code samples. Dozens of other languages created by companies other than Microsoft have been developed to work with the .NET framework. Some examples of these other languages include Python, SmallTalk, Eiffel, and COBOL. This means that you could, if you really wanted to, write pages using COBOL.Regardless of the language that you use to develop your pages, you need to understand that pages are compiled before they are executed. This means that pages can execute very quickly.The first time you request an page, the page is compiled into a .NET class, and the resulting class file is saved beneath a special directory on yourserver named Temporary Files. For each and every page, a corresponding class file appears in the Temporary Files directory. Whenever you request the same page in the future, the corresponding class file is executed.When an page is compiled, it is not compiled directly into machine code. Instead, it is compiled into an intermediate-level language called Microsoft Intermediate Language (MSIL). All .NET-compatible languages are compiled into this intermediate language.An page isn't compiled into native machine code until it is actually requested by a browser. At that point, the class file contained in the Temporary Files directory is compiled with the .NET framework Just in Time (JIT) compiler and executed.The magical aspect of this whole process is that it happens automatically in the background. All you have to do is create a text file with the source code for your page, and the .NET framework handles all the hard work of converting it into compiled code for you.ASP CLASSIC NOTEWhat about VBScript? Before , VBScript was the most popular language for developing Active Server Pages. does not support VBScript, and this is good news. Visual Basic is a superset of VBScript, which means that Visual Basic has all the functionality of VBScript and more. So, you have a richer set of functions and statements with Visual Basic.Furthermore, unlike VBScript, Visual Basic is a compiled language. This means that if you use Visual Basic to rewrite the same code that you wrote with VBScript, you can get better performance.If you have worked only with VBScript and not Visual Basic in the past, don't worry. Since VBScript is so closely related to Visual Basic, you'll find it easy to make the transition between the two languages.NOTEMicrosoft includes an interesting tool named the IL Disassembler (ILDASM) with the .NET framework. You can use this tool to view the disassembled code for any of the classes in the Temporary Files directory. It lists all the methods and properties of the class and enables you to view the intermediate-level code.This tool also works with all the controls discussed in this chapter. For example, you can use the IL Disassembler to view the intermediate-level code for the TextBox control (located in a file named System.Web.dll).About ModemTelephone lines were designed to carry the human voice, not electronic data from a computer. Modems were invented to convert digital computer signals into a form that allows them to travel over the phone lines. Those are the scratchy sounds you hear from a modem's speaker. A modem on the other end of the line can understand it and convert the sounds back into digital information that the computer can understand. By the way, the word modem stands for MOdulator/DEModulator.Buying and using a modem used to be relatively easy. Not too long ago, almost all modems transferred data at a rate of 2400 Bps (bits per second). Today, modems not only run faster, they are also loaded with features like error control and data compression. So, in addition to converting and interpreting signals, modems also act like traffic cops, monitoring and regulating the flow of information. That way, one computer doesn't send information until the receiving computer is ready for it. Each of these features, modulation, error control, and data compression, requires a separate kind of protocol and that's what some of those terms you see like V.32, V.32bis, V.42bis and MNP5 refer to.If your computer didn't come with an internal modem, consider buying an external one, because it is much easier to install and operate. For example, when your modem gets stuck (not an unusual occurrence), you need to turn it off and on to get it working properly. With an internal modem, that means restarting your computer--a waste of time. With an external modem it's as easy as flipping a switch.Here's a tip for you: in most areas, if you have Call Waiting, you can disable it by inserting *70 in front of the number you dial to connect to the Internet (or any online service). This will prevent an incoming call from accidentally kicking you off the line.This table illustrates the relative difference in data transmission speeds for different types of files. A modem's speed is measured in bits per second (bps). A 14.4 modem sends data at 14,400 bits per second. A 28.8 modem is twice as fast, sending and receiving data at a rate of 28,800 bits per second.Until nearly the end of 1995, the conventional wisdom was that 28.8 Kbps was about the fastest speed you could squeeze out of a regular copper telephone line. Today, you can buy 33.6 Kbps modems, and modems that are capable of 56 Kbps. The key question for you, is knowing what speed modems your Internet service provider (ISP) has. If your ISP has only 28.8 Kbps modems on its end of the line, you could have the fastest modem in the world, and only be able to connect at 28.8 Kbps. Before you invest in a 33.6 Kbps or a 56 Kbps modem, make sure your ISP supports them.Speed It UpThere are faster ways to transmit data by using an ISDN or leased line. In many parts of the U.S., phone companies are offering home ISDN at less than $30 a month. ISDN requires a so-called ISDN adapter instead of a modem, and a phone line with a special connection that allows it to send and receive digital signals. You have to arrange with your phone company to have this equipment installed. For more about ISDN, visit Dan Kegel's ISDN Page.An ISDN line has a data transfer rate of between 57,600 bits per second and 128,000 bits per second, which is at least double the rate of a 28.8 Kbps modem. Leased lines come in two configurations: T1 and T3. A T1 line offers a data transfer rate of 1.54 million bits per second. Unlike ISDN, a T-1 line is a dedicated connection, meaning that it is permanently connected to the Internet. This is useful for web servers or other computers that need to be connected to the Internet all the time. It is possible to lease only a portion of a T-1 line using one of two systems:fractional T-1 or Frame Relay. You can lease them in blocks ranging from 128 Kbps to 1.5 Mbps. The differences are not worth going into in detail, but fractional T-1 will be more expensive at the slower available speeds and Frame Relay will be slightly more expensive as you approach the full T-1 speed of 1.5 Mbps. A T-3 line is significantly faster, at 45 million bits per second. The backbone of the Internet consists of T-3 lines.Leased lines are very expensive and are generally only used by companies whose business is built around the Internet or need to transfer massive amounts of data. ISDN, on the other hand, is available in some cities for a very reasonable price. Not all phone companies offer residential ISDN service. Check with your local phone company for availability in your area.Cable ModemsA relatively new development is a device that provides high-speed Internet access via a cable TV network. With speeds of up to 36 Mbps, cable modems can download data in seconds that might take fifty times longer with a dial-up connection. Because it works with your TV cable, it doesn't tie up a telephone line. Best of all, it's always on, so there is no need to connect--no more busy signals! This service is now available in some cities in the United States and Europe.The download times in the table above are relative and are meant to give you a general idea of how long it would take to download different sized files at different connection speeds, under the best of circumstances. Many things can interfere with the speed of your file transfer. These can range from excessive line noise on your telephone line and the speed of the web server from which you are downloading files, to the number of other people who are simultaneously trying to access the same file or other files in the same directory.DSLDSL (Digital Subscriber Line) is another high-speed technology that is becoming increasingly popular. DSL lines are always connected to the Internet, so you don'tneed to dial-up. Typically, data can be transferred at rates up to 1.544 Mbps downstream and about 128 Kbps upstream over ordinary telephone lines. Since a DSL line carries both voice and data, you don't have to install another phone line. You can use your existing line to establish DSL service, provided service is available in your area and you are within the specified distance from the telephone company's central switching office.DSL service requires a special modem. Prices for equipment, DSL installation and monthly service can vary considerably, so check with your local phone company and Internet service provider. The good news is that prices are coming down as competition heats up.The NetWorksBirth of the NetThe Internet has had a relatively brief, but explosive history so far. It grew out of an experiment begun in the 1960's by the U.S. Department of Defense. The DoD wanted to create a computer network that would continue to function in the event of a disaster, such as a nuclear war. If part of the network were damaged or destroyed, the rest of the system still had to work. That network was ARPANET, which linked U.S. scientific and academic researchers. It was the forerunner of today's Internet.In 1985, the National Science Foundation (NSF) created NSFNET, a series of networks for research and education communication. Based on ARPANET protocols, the NSFNET created a national backbone service, provided free to any U.S. research and educational institution. At the same time, regional networks were created to link individual institutions with the national backbone service.NSFNET grew rapidly as people discovered its potential, and as new software applications were created to make access easier. Corporations such as Sprint and MCI began to build their own networks, which they linked to NSFNET. As commercial firms and other regional network providers have taken over the operation of the major Internet arteries, NSF has withdrawn from the backbone business.。

外文资料Network management software products to buyThe current market network management software can also be classified by function as follows: network element management, network management, application-layer management of the three levels, including network element management is the most basic. Now, different manufacturers have launched their own network management software, then how to choose a network management system?1.As the center of business, management needs to graspThe most fundamental one, we must know the type of network equipment, the network is organized. Therefore, we must first list all the network management needs, which are desired and what is not wanted. Through the demand for tables, we can clearly know what the functional needs in the end. After all, spend a high price does not need to buy their own service is a waste.In general, the specific needs are: to the administrator of the traffic report on the status of servers, routers, traffic on the network overload or bottleneck; through policy-based network management to initiate action, such as to stop the process to restart and so on; It should also be able to sound the alarm to the relevant personnel, such as by e-mail or pager, etc.; can provide a convenient and powerful way to show that the affected business processes, business units or even individuals.2.Application software and services for the provision of environmentalSLA (Service Level Agreement) is a response to the current services as an important indicator of the situation, and gradually as the important characteristics of network management products to look at. Therefore, a deep understanding of network management products in this important indicator of great significance to help enterprises to measure the level and degree of matching between the need to in order to make it for reporting, trend analysis and capacity planning.3.Scalability, ease of use and integration of the combinedNetwork equipment, fault type, and network management practice is a typical problem. Therefore, paragraph 3 to integrate the function of side products is very important, because most manufacturers have to rely on the No. 3 vendor to provide some added to the system so that they become more complete. Thus, scalability has become the user to choose network management solutions, an important criterion. In addition, consider the convenience of management, a number of useful network management tools must also be taken into account in order to improve the efficiency of network management.It is worth mentioning that, a great number of network management products to provide trial versions, we can try to put forward a number of enterprise applications, and only experienced the scalable, easy to use, the characteristics of a high level of integration, the product can be targeted stereotypes.4.Standards and protocols to support the independence ofSNMP standard is now mature, and produce all their products available. Truly comprehensive network management solution should support the existing and even new standards, to incorporate them into their architecture. Not only to support SNMP, but also support DHCP (Dynamic Host Configuration Protocol) and DNS, DMI(Desktop Management) and CIM (public information management). In this way, regardless of the network administrator to choose what kind of future technology or equipment, the solution can monitor and manage the entire network. Therefore, the real corporate network management solution should support all network protocols, should be able to all types of hardware and operating systems, not just some kind of close to a vendor or operating system.网管软件产品的选购目前市场销售的网络管理软件也可以按功能划分为：网元管理、网络层管理、应用层管理三个层次，其中网元管理是最基础的。

外文科技资料翻译英文原文Design Patterns in C #A model is a program using such a program, we can complete certain tasks. A model is a way through this way, we can achieve a certain purpose. Meanwhile, a model is a technology. In order to complete a particular job, we need to access and use the technology effectively. This kind of thinking can be applied to many types of work, such as : cooking, pyrotechnic, software development and other work. If the work Township respective fields is not of sound, then the practitioners in the field will be to find some common, effective solutions, using these programs, not in the circumstances to resolve the relevant issues, complete the work so as to achieve the purpose. Certain areas of regular employees in the field will have a habit of terminology These habits contribute to the terms of the work related personnel exchanges. Some models customary terms. The so-called model is able to complete some specific task and reach the goal of the mission off-the-shelf technology. With a habit of technology and related terms, some of this technology and modes documented, These records document from the customary terms to be standardized and made some effective technology has been widely disseminated.Christopher Alexander is that some of the best skills facts old road program modeled on the one of the pioneers. His research area is the architecture, not the software. In his new book, "A Pattern Language : Towns, Buildings, Construction book, "Alexander the construction of housing and urban building the successful model. Alexander's works have far-reaching effects, it also affects software fields. This Department has been able to make an impact in other areas, partly because the author has a unique purpose of the observation.You might think that the construction approach is aimed at "building design." But Alexander made clear, Application architecture model, which aims to serve the future to those living in these buildings or living in these cities people, make them feel comfortable and happy. Alexander's work showed that the model is a certain access and the exchange of technical knowledge in the field excellent way. He also pointed out that a reasonable understanding of a particular record and the object of the exercise is very crucial, this requires philosophical thinking, also faced with unpredictable challenges.Software development groups have to have a model resonates, and published a large number of books to record the software development model. These books record the software process the best time, senior architecture and software design category level, and and the pattern books are still published. If you need to choose the mode of translation of the books, Youshould first take some time to read those to the secretary of the published comments, and then from the translation of choice for your help greatest books, and as your 2020.Abstract, a kind of interface is the kind of certain methods and fields consisting of a pool. Other examples of the object can be set right through this class for a visit. Excuse the expression usually implementation of the method of operation for the functional responsibility, which often means using the name, code Notes and other documents for descriptive. Category 1 refers to the realization of the type of method to achieve code.C # language to improve the interface concept, so that it can be a separate structure, thereby interface (namely : an object must do what) and the realization (that is : a target how to meet their functional responsibilities) to effectively separate areas. C # language interface to allow for more than one category with a functional, and the C # interface can achieve more than one type interface.There are several design patterns can be used for the C # features. For example : we can use an interface to fit a certain type of interface, In reality, this is through the application adapter mode to meet a customer's needs. To discuss some language C # unable to complete the work, we should understand how the C # language is the work performed, Therefore, we first discuss the C # language interface.If you do not use interface, then you can use the abstract class (C + + language abstract). However, the n layer (n-tier) software development and definition of structure and other objects, the interface has a critical role to play. Similarly, if you do not use commissioned, then you can use the interface. If a public mandate required to be registered for a callback method, then the commission could improve these mandates, and therefore C # Entrusted language is a very useful content.1．I nterface and abstract categoryPlease indicate the C # language and abstract category of the three interfaces between different.In use, failed to provide a method of non-abstract category with an abstract interface is similar. However, we need to pay attention to the following points :A class can achieve any number of interfaces, but only up to an abstract category of sub-categories.An abstract class can include abstract, and an interface all methods in effect are abstract.An abstract class can declare and use variables, and not an interface.An abstract category of the visit Xiuchifu can be public, internal, protected, protected internal or private, and members of the interface visit Xiuchifu in default under are public, but,in a statement Interface members, allowed to use the visit Xiuchifu (even allowed to use public visit Xiuchifu).An abstract class can be defined Constructors, and not an interface.2．I nterface with the commissioningInterface with the commissioning of comparison :Interface with the commissioning of the similarities is that they can have the desired definition of the function. We learn in the process of commissioning often create some confusion and the reason was partly due to "trust" the word It can express meaning is nuanced different concepts. The right to commission and compare interface, we have to take a look at the C # language commission is how to work.C # language keyword delegate introduction of a new type of commission, This new type commissioned determine what type of method can be used only example of this type of commission. Commissioned no standard type of name, but it standardized the method parameter types and return types.We consider the following statement :Public delegate object BorrowReader ( IDataReader reader);This statement of the Declaration of a new type of commission. Commissioned by the name of the type BorrowReader. The statement said the commission can use any type of technique is, as long as the method of receiving a IDataReader object as a method parameters, and return types of methods to object. If a certain category is the following :Pricate static object GetNames (IDataReader reader){//…}GetNames () method parameter types and return types to meet BorrowReader commissioned by the types of standardized definition, this method can be used to name the types commissioned example, Examples of the statement is as follows :Is a variable b BorrowReader commissioned by the types of examples. Any visit to the commission examples of code can be called Object b, then commissioned example of the calling object b inclusive approach. The reason why the use of object example b, as this program has the following advantages : other ways in the right time calling object b and an inclusive approach. For example : a category of data services available to read on a database, called a BorrowReader commissioned example (that is, the above reader transmitted to the commission examples), then read this database as a resource for the release.C # interface can be an inclusive, C # attributes (property), and indexer. Interface can be a tolerant, inclusive but not commissioned. Why?We can simply gives the following explanation :Delegate keyword introduction of a new type, and the event keyword introduction of a new member. A statement standardized interfaces members, and not the type, time can be classified interface, which can not be classified as commissioned interface.And detailed explanation :Event keyword statement of a specific type of field (an "incident") standardize the types (must be a commissioned type) and their names. C # restrictions on the visit, the customer can not use the incident type (commissioned by the type) of all acts. Customers can only use commissioned by the + = and -= acts. Such restrictions are the result of : Only statement classes can call (or excited) an incident. However, as long as inclusive so that a certain category of a public member of the incident, a client interface types can be composed of the above examples that category. The incident is a kind of interface standard component, we have ample reason for the interface, including the incident.When entrusted to a single callback method, one based on interface design is equally effective. However, if the design needs to hold the commissioning of Togo and called method, then entrusted clearer. When a particular target for the use of a commissioned for a number of clients (for example, "hits" on the incident) for the registration, this advantage is particularly prominent. Is a one time member, the member can make an object or class to give notice to the news.Understand the language C # commissioned may be difficult, especially because we repeat the definition of "trust" the meaning of the term. For example, we can use the "commission" of the term commission statement said a commission types, and even commissioned an example. Particularly, people always say, "Call a commission," but an object can only call a commissioned example, not calling a commissioned type. If you feel this is part of some confusion hard, do not worry, a lot of people are. But we should really seriously study commissioned by the C # is how to work. which is not only to understand how the application of the key, as well as understanding how the category of interactive key.3．I nterface and attributesC # language can be an excuse for standardized interface must provide the indexer or C # attributes. If your definition of a new type of set, then we need to standardize an indexer. If you make the following statement, a realization that must include a method and the method to use an attribute value, and (or) the need to set this attribute value, then you will need a standard C # attributes.Following is a statement of a code without the use of C # attributes interface, but the realization, the need for a targeting of the attributes of the visit. Public interface IAdvertisement {Int GetID ();String GetADCopy ();Void SetADCopy (string text);}The above code interface is Oozinoz system Showproperties part of the library. In simple terms, this meant to standardize the interface of two C # attributes, but strictly speaking, they are not C # attributes. The use of C # syntax for C # attributes the advantage of its syntax more elegant. However, the most important point is not to have the capacity to foresee the reflection customers can detect the presence of C # attributes. For example, as long as the relevant attribute is the real target of C # attributes, a Datagrid object can be in one ArrayList pools showing relevant object attributes.In an interface, C # attributes expressed in the syntax is dependent, and therefore in achieving interface will have some differences. We should use in-depth understanding of C # interface characteristics of the relevant concepts and the use of details.4．I nterface detailsC # interface of the main advantages is that the interface of object interaction of the restrictions. Such restrictions are, in fact, a liberation. On the realization of a certain type of interface, the category The interface in the provision of services in the process has undergone many changes, But these changes will not affect the class customers. Although excuses are very easy to understand, but in time, Also details of the development staff have been forced to resort to reference materials.Interface description of the types of interaction in the process of the expectations and do not expect to conduct acts. Interface with pure abstract categories is very similar, interface definition it should be completed in the function, but we did not achieve these functions. Interface is also entrusted with a similar course, entrusted only to standardize the method of each method parameter and return types.Also commissioned type, it can not be an inclusive one interface commissioned and treat it as a member. However commissioned by the types of variables and marking the event keyword variables could happen in interface.Apart from the methods and events, but also inclusive interface for indexing and attributes. These elements of the syntax is very important because customers through the use of these types of members and the use of reflection, Detection and understanding to achieve category(category refers to achieve the realization of Interface) behavior. Grasp how to use the C # interface concept and very important details, that you deserve to spend some time. This part of this function is also a powerful sense of the design of the core content, as well as several of the core design pattern.5．G eneral Interface can not provide the contentC # interface can be used to simplify and strengthen the system design, of course, Sometimes the excuse that may be beyond the general interface definition and scope of use.If you want to make a kind of interface with a customer expectations interface adapter, the adapter can be applied to model.If you want to set such a simple interface, then the model can be applied appearance.If you want a definition of interface, so that it can be used to delay object, can be applied to the target group. Well, we can use synthetic model.If you want to achieve an abstract for their separation, so that they can change independently, then can be applied to bridge mode.Each model is designed to : in a specific context solve a problem. Based on the model interface emphasized the context, Context because the decision whether we need to define or redefine the right of the visit means These methods can be both a class method, it can also be a cluster approach. For example : If a particular category of what we need, However method name with the customer expectation of a name does not match, Then we can use Adapter model to solve this problem.If a client calls us to develop the code, so this is a target customers. In some cases, client code in the code only after the completion of the development, So developers can ask the households can conform to our code of the object interface specification. However, in some cases, families may also be independent of code development. For example : a rocket simulation program we need to use the information provided by the rocket, However simulation program also defines the rocket's working methods. Under such circumstances, we will find that the existing class has provided customers the services they need, but not of the same name. At this time, we can apply Adapter mode. Adapter model is aimed at : if a customer needs to use a certain type of service, This service is the category with a different interfaces, then Adapter model can be used to provide a desired interface.Java programming language and the language differences between the lies : C # Language no way any possible Cook Up Some of the anomalies in a statement. Whether this is a good character? Please give your conclusions and related reasons.In a way other than the first statement of anomalies because :We should first of all pay attention to, the Java language does not require a statement of all possible methods dished out anomalies. For example, any methods may encounter a space pointer and then dished out a statement not abnormal.Even the Java language designers admit that forced programmers all possible statement is a very unrealistic. Applications need a strategy, and under this strategy to deal with all the anomalies. Developer statement requested some type of anomaly is not a substitute for such exception handling strategy.The other : programmers should be all they can receive help. Indeed, an application architecture should have a credible strategy to deal with the anomalies. Meanwhile, forced developers in each of the methods are common problems (such as empty pointer) statement is unrealistic. For certain types of errors, such as open a file may arise in the course of the issue, there is a definite need for methods the caller to deal with the anomalies that may occur. C # language for a method statement terminology might happen some unusual statement from the method in addition to the first. In fact, this program is pouring out the water at the same time, the children are thrown out of.Object-oriented program design procedures can be avoided is not designed for a single, thus avoiding the procedures of the various parts are mixed together. An ideal object-oriented application should be one of the smallest category, This category could include other reusable kind of behavior effectively together.中文译文C#设计模式一个模式是一种方案，利用这种方案，我们可以完成某项工作。

Visual Basic language and arithmeticThe United States launched the Microsoft Visual Basic (may be referred to VB), is the latest version of the current VB 2008 Beta2 (VB9) Chinese version.Visual meaning the visual, visible, referring to the development of operating systems like windows graphical user interface (Graphic User Interface, GUI) method, it does not need to prepare a large number code to describe the appearance of the interface elements and location, as long as the pre - The establishment of good drag and drop objects on the screen corresponding to the location.Basic is actually an abbreviation of the phrase; this phrase is Beginners all-purpose symbolic instruction code, the Chinese meaning "to the initial directive GM symbol code language."Visual Basic learning, Professional Edition and Enterprise Edition versions to meet the different needs of the development. Study and apply to the ordinary version of the majority of learners and the use of Visual Basic development of the general staff of Windows applications, but; professional version for computer professional development of staff, including the study of functional version of the full content control and Internet development tools such as advanced features ,Enterprise contain not only all the professional version of the content, there are automated tools such as Component Manager, professional programmers to make the development of a powerful group essence of distributed applications.Visual BasicSection 1 the summary of Visual BasicMicrosoft Visual Basic,( abbreviate VB )as tool the most of application program one of under Windows operating platform. No matter beginner or professional developer, VB has all offered a whole set of tools to them, Development application program that it can be relaxed and convenient. So VB as most computer first-selected the ABC of programming language of beginner." Visual" mean method to adopt visual user of development figure interface (GUI), need and write a large number of code go and describe interface appearance and position of element seldom, Tow and show controlling part that need corresponding position to get screen can help figure design interface, user of figure,; " Basic" means BASIC language, because VB is developed on the basis of already existing BAISC language.VB is a kind of programming language in common use of Microsoft, It, including VBA of the numerous Windows application software use VB language in Microsoft Excel, Microsoft Accessed., For users to carry on the secondary development; Make web page use more VBScript script language sub collection of VB too at present.Utilize data of VB visit characteristic user can establish the data base to most data base forms including Microsoft SQL Server and other enterprises data base With the application program of front, and adjustable service end part. Utilize ActiveX(TM) technology, VB can use word processor, electronic data list he Windows function that application program offers extremely, Excel of Microsoft,, Word of Microsoft,, Even can use by VB specialty edition or enterprise application program and target thatedition establish directly.The procedure that users established finally is a real .EXE file , can issue freely .VB offer study edition, the specialty edition and enterprise edition, use to satisfied with different development demands. Study edition make programming personnel develop Windows and Windows application program of NT very easily. The specialty edition has offered the developing instrument with complete function to programming personnel of the specialty, Include studying all functions of edition in the specialty edition. Enterprise edition allow the professional personnel to establish strong distributed application program in the form of group. It includes all characteristics of the specialty edition. So can choose different editions according to different needs.Section 2 integrated development environmentsIntegrated environment of VB call IDE, made up of a lot of parts , include title board, menu fence, tool fence, controlling part case, And window body window, engineering management device window, attribute window, code window and window body overall arrangement window body overall arrangement, etc. of designing etc.. Have covered all functions, such as design which develops the application program, editting, compiling and debugging, etc..In VB, the application program calls the project too. When start VB and open a new project for the first time, can see and pursue integrated development environment interface that show.Visual Basic Integrated development environmentVB come and organize development of application program through project, use project come and manage and form files of application program. One project uses the environment to make up by several window bodies, standard module generally. The system manages project through the project menu, for instance add the window body, quote . System allow turn on and manage a lot of projects besides.Section 3 Visual Basic language brief introductionsBasic use and do the elementary high-level language that used often most. Its full name is Beginner' s All-purpose Symbolic Instruction Code, abbreviate as BASIC. As its name suggests, Basic one specially for language that beginner design, because it easy to learn easy to know, So the body is popular. Early Basic language to belong to and solve translating type, so can carry out line by line , So it can see the result carried out at once , this is a very convenient design for beginner. But it have concept of structure either, one that is in procedure maintain and management have as much as other language problems. But back-end Basic correct shortcoming of the above (such as Quick Basic), make it may used for and develop the large-scaler procedure too.The language is the basic composition, which forms VB procedure. VB has stipulated the form of sentences and function.Grammar:The sentence defines incantations [Sentence body]Sentence define agree with and used in fixed function of sentence, sentence body appoint concrete content or want concrete operation that carry out of sentence. All set of sentence VB language, carry on with VB sentence organic association finish acertain specific function the procedure. Interface + procedure can solve a certain application problem.VB application program code window write in" code editing machine" generally. " editing machine of code" is like the word processing software of a piece of height specialization, there are many easies function of writing VB code, Pursue to show [Example Ex-Hello ]In" code editing machine" code that window written.“Editing machine of code” windowSection 4 develop the application program with Visual BasicUse VB programming, design appearance of application program first generally, write every target procedure code or other treatment procedure of incident respectively, Work of programming should be light more.The procedure of establishing the application program is as follows:Establish application program interfaceThe interface is the mutual bridge of user and procedure, Generally formed of window body and vision frame of the button, menu, text frameset. with standard WINDOWS interface of application program that VB establish. Require according to function of procedure and user and need of information interchange of procedure, Come to confirm that need those targets , plan the overall arrangement of the interface.2. Design by each attributes of target in interfaceDemand and set up each attribute of target such as appearance, name,, size of targeted. according to interface of planning.Most attribute person who fetch can set up through the attribute window when design already, Too can set up revising when operating in procedure through programming in procedure code. Have the targets respond programming by procedure code3. Respond procedure code of programming targetInterface determine appearance of procedure only, design window add codes through" code editing machine" soon after the interface, Realize some make the tasks, such as responding, information processing,etc. after accepting external message, Add code , realize some response, information processing that make after accepting external information task, As editor's window of code pursued shows add codes “code editing machine” wi ndow4. Keep projectOne VB procedure one project, at the time of designing a application program, system will set up one be expanded and called. Project file of vbp, project file include all relevant information of file that project set up this, Keep project keep associated documents of project this at the same time. For example the window body produced when design interfaces is kept and being expanded and being called. Frm sum. In the window body of foxfire. At the time of opening a project( file), this project relevant files load at the same time.5. Operate and debugged by procedureOperate the procedure thoroughpin operate" selecting in the menu, when the mistake appears, VB system can offer information prompt can looked for and get ridof the mistake thoroughpin debug" within operate" menus too.6. Can produce by executive programFor make procedure can break away from VB environment, order to become next life through" file"" producing project 1.exe" of menu but executive program (eyeful), Can carry out this file directly after this. In produce, + executive program, and then through install guide bale all associated documents, Can run independently after installation under the environment of windows 9 x/2000 as a software product.In computer system's any software, is by the every large or small each kind of software constituent constitution, defers to the specific algorithm to realize respectively, the algorithm quality direct decision realizes the software performance fit and unfit quality. Designs the algorithm with any method, what resources designs the algorithm to need, requires how many running time, how many storage space, how to determine an algorithm the quality, when realizes a software, is must give to solve. In computer system's operating system, the language compiling system, the database management system as well as in various computer application system's software, must use each one concrete algorithm to realize. Therefore, the algorithm design and the analysis are the computer science and a technical core question.The algorithm is the problem-solving step, we may define the algorithm Cheng Jie a determination class question the random one special method. In the computer science, the algorithm needs to use the computer algorithmic language to describe, the algorithm represents with the computer solves a kind of question precisely, the effective method. The algorithm construction of data = procedure, solves one to assign may calculate or the solvable question, the different person may compile the different procedure, solves the identical problem, here has two problems: First, with computational method close related algorithm question; Second, programming technical question. Between the algorithm and the procedure has the close relationship. The algorithm is a group has the poor rule, they had stipulated solves some specific type question a series of operations, is to the problem solving plan accurate and the complete description. Formulates an algorithm, generally must pass through stages and so on design, confirmation, analysis, code, test, debugging, time. To algorithm study including five aspect contents:① Design algorithm. The algorithm design work is impossible completely the automation, should study the understanding already by the practice to prove that was the useful some basic algorithm design method, these basic design method was not only suitable for the computer science, moreover was suitable for domains and so on electrical engineering, operations research;②Expresses the algorithm. The description algorithm's method has many kinds of forms, for example the natural language and the algorithmic language, have the suitable environment and the characteristic respectively;③Confirms the algorithm. The algorithm confirmed the goal is causes the people to believe firmly that this algorithm can work unmistakably correctly, namely this algorithm has the circularity. The correct algorithm describes with the computer algorithmic language, constitutes the computer program, the computer program moves on the computer, obtains thealgorithm operation result;④ Parsing algorithm. The algorithmic analysis is requires how many computing time and the storage space to an algorithm makes the quota the analysis. The parsing algorithm may forecast that what environment this algorithm does suit in moves effectively, to solves the identical question different algorithm validity to make the comparison;⑤ Confirmation algorithm. With machine language description algorithm whether can calculate effectively, reasonable, must carry on the test to the procedure, the test order work and makes the space and time distribution map by the debugging to be composed.But the algorithm has certain characteristic, it includes:①Determinism. Algorithm each kind of operation must have the determination significance, this kind of operation should carry out what kind of movement should not to have the ambiguity, the goal is clear;②Effectiveness. Requests the operation which in the algorithm waits for realizing is basic, each kind of operation can at least completes in the principle by the human with the paper and the pen in the limited time;③ Input. An algorithm has 0 or the many inputs, before the algorithm operation starts gives the algorithm to need the data the starting value, these inputs are from the specific object set;④Output. Does for the algorithm operation result, an algorithm has or many outputs, the output has some kind of specific relational quantity with the input;⑤ Has poor. An algorithm always after carrying out had the poor step operation has terminated, namely this algorithm was may reach.Satisfies a first four characteristic group of rule not to be able to be called the algorithm, can only be called the computational process, the operating system is a computational process example, the operating system uses for to manage the computer resources, controls the manufacture industry movement, when has not made industry the movement, the computational process does not stop, but is at the waiting status.The algorithm complexity is the algorithm efficiency measure, when appraises the algorithm performance, the complexity is an important basis. The algorithm complex degree with moves computer resources how many which this algorithm needs related, needs the resources are more, indicated that this algorithm the complexity is higher; Needs the resources are less, indicated that this algorithm the complexity is lower.The spatial resources, which computer’s resources, operate most importantly, needs the time which and the stored routine and the data need, the algorithm complexity has division time complexity and the spatial complexity.The algorithm carries out the operation on the computer, needs the data which certain storage space depositing description algorithm the procedure and the algorithm need, the computer completes the operation task to require certain time. The procedure which writes according to the different algorithm places when on the computer operates, needs the time and the space are different, the algorithm complexity is needs the time and the spatial one kind of measure to the algorithm operation. The different computer its operating speed difference is very big, is weighing an algorithm the complexity to note this point.Regarding question, which assigns willfully, a profitable target which designs,the complex low algorithm is as far as possible when designs algorithm considered. Moreover, when the question, which assigns already when has many kinds of algorithms, an important criterion which choice complexity low, is when selects algorithm should follow. Therefore, the algorithm complex analysis or selects to the algorithm design has the important guiding sense and the use value.When discussion algorithm complexity, two questions need to clarify:(1) An algorithm's complexity expresses with what kind of quantity;(2) How to calculate one to assign the algorithm the complexity. After finding solves a question the algorithm, is this algorithm realization, as for whether could find the method which realized, was decided in the algorithm circularity and the computation complexity, whether this question did have the solution algorithm, whether to provide the time resources which and the spatial resources the algorithm needed.Visual Basic 语言与算法1991年，美国微软公司推出了Visual Basic(可简称VB），目前的最新版本是VB 2008 Beta2(VB9)中文版。

英文资料翻译Computer Language and ProgrammingI. IntroductionProgramming languages, in computer science, are the artificial languages used to write a sequence of instructions (a computer program) that can be run by a computer. Similar to natural languages, such as English, programming languages have a vocabulary, grammar, and syntax. However, natural languages are not suited for programming computers because they are ambiguous,meaning that their vocabulary and grammatical structure may be interpreted in multiple ways. The languages used to program computers must have simple logical structures, and the rules for their grammar, spelling, and punctuation must be precise.Programming languages vary greatly in their sophistication and in their degree of versatility. Some programming languages are written to address a particular kind of computing problem or for use on a particular model of computer system. For instance, programming languages such as FORTRANandCOBOLwere written to solve certain general types of programming problems—FORTRAN for scientific applications, and COBOL for business applications. Although these languages were designed to address specific categories of computer problems, they are highly portable, meaning that they may be used to program many types of computers. Other languages, such as machine languages, are designed to be used by one specific model of computer system, or even by one specific computer in certain research applications. The most commonly used programming languages are highly portable and can be used to effectivelysolve diverse types of computing problems. Languages like C, PASCALand BASIC fall into this category.II. Language TypesProgramming languages can be classified as either low-level languages or high-level languages. Low-level programming languages, or machine languages, are the most basic type of programming languages and can be understood directly by a computer. Machine languages differ depending on the manufacturer and model of computer. High-level languages are programming languages that must first be translated into a machine language before they can be understood and processed by a computer. Examples of high-level languages are C, C++, PASCAL, and FORTRAN. Assembly languages are intermediate languages that are very close to machine languages and do not have the level of linguistic sophistication exhibited by other high-level languages, but must still be translated into machine language.1. Machine LanguagesIn machine languages, instructions are written as sequences of 1s and 0s, called bits, that a computer can understand directly. An instruction in machine languagegenerally tells the computer four things: (1) where to find one or two numbers or simple pieces of data in the main computer memory (Random Access Memory, or RAM), (2) a simple operation to perform, such as adding the two numbers together, (3) where in the main memory to put the result of this simple operation, and (4) where to find the next instruction to perform. While all executable programs are eventually read by the computer in machine language, they are not all programmed in machine language. It is extremely difficult to program directly in machine language because the instructions are sequences of 1s and 0s. A typical instruction in a machine language might read 10010 1100 1011 and mean add the contents of storage register A to the contents of storage register B.2. High-Level LanguagesHigh-level languages are relatively sophisticated sets of statements utilizing words and syntax from human language. They are more similar to normal human languages than assembly or machine languages and are therefore easier to use for writing complicated programs. Theseprogramming languages allow larger and more complicated programs to be developed faster. However, high-level languages must be translated into machine language by another program called a compiler before a computer can understand them. For this reason, programs written in a high-level language may take longer to execute and use up more memory than programs written in an assembly language.3. Assembly LanguagesComputer programmers use assembly languages to make machine-language programs easier to write. In an assembly language, each statement corresponds roughly to one machine language instruction. An assembly language statement is composed with the aid of easy to remember commands. The command to add the contents of the storage register A to the contents of storage register B might be written ADD B, A in a typical assembly language statement. Assembly languages share certain features with machine languages. For instance, it is possible to manipulate specific bits in both assembly and machine languages. Programmers use assembly languages when it is important to minimize the time it takes to run a program, because the translation from assembly language to machine language is relatively simple. Assembly languages are also used when some part of the computer has to be controlled directly, such as individual dots on a monitor or the flow of individual characters to a printer.III. Classification of High-Level LanguagesHigh-level languages are commonly classified as procedure-oriented, functional, object-oriented, or logic languages. The most common high-level languages today are procedure-oriented languages. In these languages, one or more related blocks of statements that perform some complete function are grouped together into a program module, or procedure, and given a name such as “procedure A.” If the same sequence of operations is needed elsewhere in the program, a simple statement can be used to refer back to the procedure. In essence, a procedure is just amini-program. A large program can be constructed by grouping together procedures that perform different tasks. Procedural languages allow programs to beshorter and easier for the computer to read, but they require the programmer to design each procedure to be general enough to be usedin different situations.Functional languages treat procedures like mathematical functions and allow them to be processed like any other data in a program. This allows a much higher and more rigorous level of program construction. Functional languages also allow variables—symbols for data that can be specified and changed by the user as the program is running—to be given values only once. This simplifies programming by reducing the need to be concerned with the exact order of statement execution, since a variable does not have to beredeclaredor restated, each time it is used in a program statement. Many of the ideas from functional languages have become key parts of many modern procedural languages.Object-oriented languages are outgrowths of functional languages. In object-oriented languages, the code used to write the program and the data processed by the program are grouped together into units called objects. Objects are further grouped into classes, which define the attributes objects must have. A simple example of a class is the class Book. Objects within this class might be Novel and Short Story. Objects also have certain functions associated with them, called methods. The computer accesses an object through the use of one of the object’s methods. The method performs some action to the data in the object and returns this value to the computer.Classes of objects can also be further grouped into hierarchies, in which objects of one class can inherit methods from another class. The structure provided in object-oriented languages makes them very useful for complicated programming tasks.Logic languages use logic as their mathematical base. A logic program consists of sets of facts and if-then rules, which specify how one set of facts may be deduced from others, for example: If the statement X is true, then the statement Y is false. In the execution of such a program, an input statement can be logically deduced from other statements in the program. Many artificial intelligence programs are written in such languages.IV. Language Structure and ComponentsProgramming languages use specific types of statements, or instructions, to provide functional structure to the program. A statement in a program is a basic sentence that expresses a simple idea—its purpose is to give the computer a basic instruction. Statements define the types of data allowed, how data are to be manipulated, and the ways that procedures andfunctions work. Programmers use statements to manipulate common components of programming languages, such as variables and macros (mini-programs within a program). Statements known as data declarations give names and properties to elements of a program called variables. Variables can be assigned different values within the program. The properties variables can have are called types, and they include such things as what possible values might be saved in the variables, how much numerical accuracy is to be used in the values, and how one variable may represent a collection of simpler values in an organized fashion, such as a table or array. In many programming languages, a key data type is a pointer. Variables that are pointers do not themselves have values; instead, they have information that the computer can use to locate some othervariable—that is, they point to another variable.An expression is a piece of a statement that describes a series of computations to be performed on some of the program’s variables, such as X+Y/Z, in which the variables are X, Y, and Z and the computations are addition and division. An assignment statement assigns a variable a value derived from some expression, while conditional statements specify expressions to be tested and then used to select which other statements should be executed next.Procedure and function statements define certain blocks of code as procedures or functions that can then be returned to later in the program. These statements also define the kinds of variables and parameters the programmer can choose and the type of value that the code will return when an expression accesses the procedure or function. Many programming languages also permit minitranslation programs called macros. Macros translate segments of code that have been written in a language structure defined by the programmer into statements that the programming language understands.V. HistoryProgramming languages date back almost to the invention of the digital computer in the 1940s. The first assembly languages emerged in the late 1950s with the introduction of commercial computers. The first procedural languages were developed in the late 1950s to early 1960s:FORTRAN, created by John Backus, and then COBOL, created by Grace Hopper The first functional language was LISP, written by John McCarthy4 in the late 1950s. Although heavily updated, all three languages are still widely used today. In the late 1960s, the first object-oriented languages, such as SIMULA, emerged. Logic languages became well known in the mid 1970swith the introduction of PROLOG6, a language used to program artificial intelligence software. During the 1970s, procedural languages continued to develop with ALGOL, BASIC, PASCAL, C, andAdaSMALLTALKwas a highly influential object-oriented language that led to the merging ofobject-oriented and procedural languages in C++ and more recently in JA V A10. Although pure logic languages have declined in popularity, variations have become vitally important in the form of relational languages for modern databases, such as SQL.计算机程序一、引言计算机程序是指导计算机执行某个功能或功能组合的一套指令。

计算机英汉翻译外文原文Introduction to Javaautor：Martin Ngobye.source：Computing Static Slice for Java ProgramsJava is designed to meet the challenges of application development in the context of heterogeneous, network-wide distributed environments. Paramount among these challenges is secure delivery of applications that consume the minimum of system resources, can run on any hardware and software platform,and can be extended dynamically.Java originated as part of a research project to develop advanced software for a wide variety of network devices and embedded systems. The goal was to develop a small, reliable, portable, distributed, real-time operating platform. When the project started, C++ was the language of choice. But over time the difficulties encountered with C++ grew to the point where the problems could best be addressed by creating an entirely new language platform. Design and architecture decisions drew from a variety of languages such as Eiffel, SmallTalk, Objective C, and Cedar/Mesa. The result is a language platform that has proven ideal for developing secure, distributed, networkbasedend-userapplicationsinenvironmentsrangingfromnetwork-embedded devices to the World-Wide Web and the desktop.The design requirements of Java are driven by the nature of the computing environments in which software must be deployed.The massive growth of the Internet and the World-Wide Web leads us to a completely new way of looking at development and distribution of software. To live in the world of electronic commerce and distribution, Java must enablethe development of secure, high performance, and highly robust applications on multiple platforms in heterogeneous, distributed networks.Operating on multiple platforms in heterogeneous networks invalidates the traditional schemes of binary distribution, release, upgrade, patch, and so on. To survive in this jungle, Java must be architecture neutral, portable, and dynamically adaptable.The Java system that emerged to meet these needs is simple, so it can be easily programmed by most developers; familiar, so that current developers can easily learn Java; object oriented, to take advantage of modern software developmentmethodologies and to fit into distributed client-server applications; multithreaded, for high performance in applications that need to perform multiple concurrent activities, such as multimedia; and interpreted, for maximum portability and dynamic capabilities.Together, the above requirements comprise quite a collection of buzzwords, so let’s examine some of them and their respective benef its before going on.What’s completely new is the manner in which Java and its run-time system have combined them to produce a flexible and powerful programming system..Developing your applications using Java results in software that isportable across multiple machine architectures, operating systems, andgraphical user interfaces, secure, and high performance, With Java, your jobas a software developer is much easier―you focus your full attention on the end goal of shipping innovative products on time, based on the solidfoundation of Java. The better way to develop software is here, now, broughtto you by the Java language platform.Very dynamic languages like Lisp, TCL, and SmallTalk are often used for prototyping. One of the reasons for their success at this is that they arevery robust―you don’t have to worry about freeing or corrupting memory.Similarly, programmers can be relatively fearless about dealing with memory when programming in Java, The garbage collection system makes thep rogrammer’s job vastly easier; with the burden of memory management taken off the programmer’s shoulders, storage allocation errors go away. Another reason commonly given that languages like Lisp, TCL, and SmallTalk are good for prototyping is that they do n’t require you to pin down decisions early on―these languages are semantically rich.Java has exactly the opposite property: it forces you to make explicit choices. Along with these choices come a lot of assistance―you can write method invocations and, if you get something wrong, you get told about it at compile time. You don’t have to worry about method invocation error.中文翻译JAVA介绍作者：Martin Ngobye.出处：Computing Static Slice for Java ProgramsJava是被设计用来解决在上下文分布式的异构网络中应用程序开发的问题。