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外文文献原稿和译文原稿DATABASEA database may be defined as a collection interrelated data store 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 controlled approach is used in adding new data and in modifying and retrieving existing data within the data base .One system is said to contain a collection of database if they are entirely separate in structure .A database may be designed for batch processing , real-time processing ,or in-line processing .A data base system involves application program, DBMS, and database.THE INTRODUCTION TO DATABASE MANAGEMENT SYSTEMSThe term database is often to describe a collection of related files that is organized into an integrated structure that provides different people varied access to the same data. In many cases this resource is located in different files in different departments throughout the organization, often known only to the individuals who work with their specific portion of the total information. In these cases, the potential value of the information goes unrealized because a person in other departments who may need it does not know it or it cannot be accessed efficiently. In an attempt to organize their information resources and provide for timely and efficient access, many companies have implemented databases.A database is a collection of related data. By data, we mean known facts that can be recorded and that have implicit meaning. For example, the names, telephone numbers, and addresses of all the people you know. You may have recorded this data in an indexed address book, or you may have stored it on a diskette using a personalcomputer and software such as DBASE Ⅲor Lotus 1-2-3. This is a collection of related data with an implicit meaning and hence is a database.The above definition of database is quite general. For example, we may consider the collection of words that made up this page of text to be usually more restricted. A database has the following implicit properties:● A database is a logically coherent collection of data with some inherent meaning. A random assortment of data cannot be referred to as a database.● A database is designed, built, and populated with data for a specific purpose. It has an intended group of user and some preconceived applications in which these users are interested.● A database represents some aspect of the real world, sometimes called the miniworld. Changes to the miniworld are reflected in the database.In other words, a database has some source from which data are derived, some degree of interaction with events in the real world, and an audience that is actively interested in the contents of the database.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; and (3) 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-date information to make effective decisions.●Customers 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.A DBMS can organize, process, and present selected data elements from 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 p oorly defined, but people can “browse” through the database until they have the needed information. In short, the DBMS will “mange” the stored data items and assemble the needed items from the common database in response to the queries of those who aren’t programmers. In a file-oriented system, user needing special information may communicate their needs to a programmer, who, when time permits, will write one or more programs to extract the data and prepare the information. The availability of a DBMS, however, offers users a much faster alternative communications path.DATABASE QUERYIf the DBMS provides a way to interactively enter and update the database ,as well as interrogate it ,this capability allows for managing personal database. However, it does not automatically leave an audit trail of actions and does not provide the kinds of controls necessary in a multi-user organization .There controls are only available when a set of application programs is customized for each data entry and updating function.Software for personal computers that perform some of the DBMS functions has been very popular .Individuals for personal information storage and processing intended personal computers for us .Small enterprises, professionals like doctors, architects, engineers, lawyers and so on have also used these machines extensively. By the nature of intended usage ,database system on there machines are except from several of the requirements of full-fledged database systems. Since data sharing is not intended, concurrent operations even less so ,the software can be less complex .Security and integrity maintenance are de-emphasized or absent .as data volumes will be small, performance efficiency is also less important .In fact, the only aspect of a database system that is important is data independence. Data independence ,as stated earlier ,means that application programs and user queries need not recognize physical organization of data on secondary storage. The importance of this aspect , particularly for the personal computer user ,is that this greatly simplifies database usage . The user can store ,access and manipulate data at ahigh level (close to the application)and be totally shielded from the low level (close to the machine )details of data organization.DBMS STRUCTURING TECHNIQUESSpatial data management has been an active area of research in the database field for two decades ,with much of the research being focused on developing data structures for storing and indexing spatial data .however, no commercial database system provides facilities for directly de fining and storing spatial data ,and formulating queries based on research conditions on spatial data.There are two components to data management: history data management and version management .Both have been the subjects of research for over a decade. The troublesome aspect of temporal data management is that the boundary between applications and database systems has not been clearly drawn. Specifically, it is not clear how much of the typical semantics and facilities of temporal data management can and should be directly incorporated in a database system, and how much should be left to applications and users. In this section, we will provide a list of short-term research issues that should be examined to shed light on this fundamental question.The focus of research into history data management has been on defining the semantics of time and time interval, and issues related to understanding the semantics of queries and updates against history data stored in an attribute of a record. Typically, in the context of relational databases ,a temporal attribute is defined to hold a sequence of history data for the attribute. A history data consists of a data item and a time interval for which the data item is valid. A query may then be issued to retrieve history data for a specified time interval for the temporal attribute. The mechanism for supporting temporal attributes is to that for supporting set-valued attributes in a database system, such as UniSQL.In the absence of a support for temporal attributes, application developers who need to model and history data have simply simulated temporal attributes by creating attribute for the time interval ,along with the “temporal” attribute. This of course may result in duplication of records in a table, and more complicated search predicates in queries. The one necessary topic of research in history data management is to quantitatively establish the performance (and even productivity) differences betweenusing a database system that directly supports attributes and using a conventional database system that does not support either the set-valued attributes or temporal attributes.Data security, integrity, and independenceData security prevents unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database of the database, called subschemas. For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data.Data integrity refers to the accuracy, correctness, or validity of the data in the database. In a database system, data integrity means safeguarding the data against invalid alteration or destruction. In large on-line database system, data integrity becomes a more severe problem and two additional complications arise. The first has to do with many users accessing the database concurrently. For example, if thousands of travel agents book the same seat on the same flight, the first agent’s booking will be lost. In such cases the technique of locking the record or field provides the means for preventing one user from accessing a record while another user is updating the same record.The second complication relates to hardware, software or human error during the course of processing and involves database transaction which is a group of database modifications treated as a single unit. For example, an agent booking an airline reservation involves several database updates (i.e., adding the passenger’s name and address and updating the seats-available field), which comprise a single transaction. The database transaction is not considered to be completed until all updates have been completed; otherwise, none of the updates will be allowed to take place.An important point about database systems is that the database should exist independently of any of the specific applications. Traditional data processing applications are data dependent.When a DMBS is used, the detailed knowledge of the physical organization of the data does not have to be built into every application program. The application program asks the DBMS for data by field name, for example, a coded representationof “give me customer name and balance due” would be sent to the DBMS. Without a DBMS the programmer must reserve space for the full structure of the record in the program. Any change in data structure requires changes in all the applications programs.Data Base Management System (DBMS)The system software package that handles the difficult tasks associated with creating ,accessing and maintaining data base records is called a data base management system (DBMS). 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 “.At the present time ,there are four underling structures for database management systems. They are :List structures.Relational structures.Hierarchical (tree) structures.Network structures.Management Information System(MIS)An MIS can be defined as a network of computer-based data processing procedures developed in an organization and integrated as necessary with manual and other procedures for the purpose of providing timely and effective information to support decision making and other necessary management functions.One of the most difficult tasks of the MIS designer is to develop the information flow needed to support decision making .Generally speaking ,much of the information needed by managers who occupy different levels and who have different levels and have different responsibilities is obtained from a collection of exiting information system (or subsystems)Structure Query Language (SQL)SQL is a data base processing language endorsed by the American NationalStandards Institute. It is rapidly becoming the standard query language for accessing data on relational databases .With its simple ,powerful syntax ,SQL represents a great progress in database access for all levels of management and computing professionals.SQL falls into two forms : interactive SQL and embedded SQL. Embedded SQL usage is near to traditional programming in third generation languages .It is the interactive use of SQL that makes it most applicable for the rapid answering of ad hoc queries .With an interactive SQL query you just type in a few lines of SQL and you get the database response immediately on the screen.译文数据库数据库可以被定义为一个相互联系的数据库存储的集合。
UNDERSTANDING CANADIAN BUSINESSCHAPTER # 1 noteschater1MANAGING WITHIN THE DYNAMIC BUSINESS ENVIRONMENT动态商业环境下的管理Business and Entrepreneurship: Revenues, Profits, and Losses 事业和企业家能力:收益，利益和损失Business: Any activity that seeks to provide goods and services to others while operating at a profit.事业：寻求当在一笔利润操作时向其他人提供货物和服务的任何活动。
Profit: The amount a business earns beyond what it spends for salaries and other expenses.利益:一种商业在它为了薪金和其他话费所话费的以外赚的量Entrepreneur: A person who risks time and money to start and manage a business.企业家能力:冒险用时间和金钱开始和管理一种商业的一个人Revenue: The total amount of money a business takes in during a given period by selling goods and services. 收益:一种商业在一段特定的时间期间通过出售商品和服务获得的金钱Loss: When a business’s expenses are more then its revenue.失去：当一种商业的花费超过其收益时Risk: The chance an entrepreneur takes of losing time and money on a business that may not prove profitable.风险：一个企业家浪费了时间和金钱在事业上,却无利可图的机会Responding to the Various Business Stakeholders对各种各样的傻瓜也既得利益者作出反应Stakeholder:All the people who stand to gain or lose by the policies andactivities of a business.财产保管人：他通过政策和一种商业活动赢得或者失去的所有人- Investors; invest in the business投资者：在商业中的投资- Financial Institutions; lend money to the business 金融的社会公共机构:借钱给企业- Supplier; sell to the business供应商：向企业卖物品- Customers; buy goods and services from the business 消费者：从企业中购买商品和服务- Government; gets taxes from the business 政府：从企业中收税- Employees; get jobs from the business受雇者：从企业中得到工作- Dealers; buy and sell for the business经销商：为企业进行交易买卖- Environmentalists; protest the businesses pollution habits环境保护主义者：抗议商业污染习惯- Surrounding Community; get many positives and negatives from the business 周围的社区：从商业之中得到很多积极的和消极的影响Outsourcing: Assigning various functions, such as accounting, production, security, maintenance, and legal work, to outside organizations.外包:委托给外部单位的业务有很多,像审计,产品,安全,维护保养和政法工作.There is a major trend toward outsourcing in North Americanbusiness in an effort to cut costs and become more competitive. Much production has moved off shore, and many management functions are now sub contracted to external sources such as consulting firms.在北美的外包业务有一个大致的发展趋势:就是努力缩减成本提高竞争力.很多的产品现在已经转移到了沿海地区,许多管理职能现在订约与外部资源像咨询公司.Using Business Principles in Non-profit Organization非营利组织的商业原则的应用Non- profit Organization: An organization whose goals do not include making a personal profit for its owners or organization. 无利益组织：其目标不包括为其所有者或者组织赚取一笔个人的利润的一个组织。
firebase realtime database安全规则Firebase是一个广泛使用的后端服务和开发平台，它提供了多种云服务，其中包括实时数据库。
Firebase实时数据库是一种云托管的NoSQL数据库，可以进行实时同步和持久化数据存储。
在使用Firebase实时数据库时，保护和控制数据库中的数据成为一个非常重要的问题。
为了解决这个问题，Firebase提供了一种叫做"实时数据库安全规则"的功能。
本文将深入探讨实时数据库安全规则的特点、用法和一些最佳实践。
实时数据库安全规则是用于保护Firebase实时数据库中数据访问的策略。
通过这些规则，可以定义谁可以读取和写入数据库中的数据，以及如何限制和控制对数据的访问。
通过在Firebase控制台上设置这些规则，可以确保只有经过授权的用户才能访问和修改数据，从而保护数据的安全性和完整性。
在开始之前，我们需要了解一些基本概念。
Firebase实时数据库中的数据以"JSON树"的形式组织。
每个节点都有一个唯一的URL，可以通过该URL 来访问和操作节点的数据。
此外，实时数据库支持四种基本的数据操作：读取、写入、更新和删除。
实时数据库安全规则是一个由JSON对象构成的规则集合。
这些规则定义了在进行数据读取和写入时所需满足的条件。
默认情况下，如果没有为数据库设置安全规则，任何人都可以读取和写入数据。
因此，设置适当的安全规则是非常重要的，以保护敏感数据免受未经授权的访问。
那么，如何设置实时数据库的安全规则呢？下面是一步一步的指南：第一步：理解实时数据库安全规则的结构实时数据库安全规则由三个部分构成：规则集合、规则和权限控制。
规则集合是实时数据库中所有规则的组合。
您可以为不同的节点设置不同的规则集合。
规则是特定节点上的规则配置。
每个规则包括路径、条件和允许的操作。
权限控制定义了谁可以访问数据库中的数据。
您可以细粒度地控制用户的访问权限。
Cyber risk is the thing that exists forever, with the rapid development of computer technology, computer processing services, document processing, office automation and we are using the Internet, intranet or any other based on information technology and network, the risk will comes every day to cost the damage for service, hardware, network and software to us.Therefore the security concern is necessary to be established to protect us from hacker’s attack and abuse cases which can affect our system. So for cyber security issues, should be like every household fire alarm problems, take preventive measures.For network operator and manager, access to the local network, information reading and writing operations are protected and controlled, to avoid a "trap door", viruses, unauthorized access, denial of service and network resource control illegal occupation and illegal threats, stop and defence network hackers.Typically, system security, performance and functionality is a contradiction relationship. If a system does not provide any services to the outside, there is impossible to encounter a security threat. However, companies have to access to international network, to provide online stores and e-commerce services etc. to customers, therefore convert an internal closed network to an open network environment, that would be a variety of security issues, including systemic issues also will occurring.Security objectives through the system and network security configuration, application firewalls and intrusion detection, security scanning, network anti-virus technology, import and export information strict control; detect the devices on the network, analyze and evaluate, find and reporting system memory weaknesses and vulnerabilities, assess security risks and recommending remedial measures, and effectively prevent the spread of the virus and hacking, monitoring the status of the entire network.Security for enterprise system should involve:Attack Monitoring: Through specific network segment, the monitoring system, most of hacker’s attacks can be detected in real time, and take defence action (such as disconnected from the network, recording the attack process, track the attack source, etc.).Encrypt the communication: active encrypted communications, therefore attacker cannot understand, modify sensitive information.Authentication: A good authentication system can prevent an attacker to spoof a legitimate user.Backup and restore: a good backup and recovery mechanisms can cause losses in the attack, as soon as possible to restore data and provide system services.Multiple layers of defense, the attacker first line of defense after the break, delay or block its reach targets.Hidden inside information, so an attacker cannot understand the basic situation within the system.Security monitoring centre should be set up to provide a safety information management systems, monitoring, and emergency care services.Due to the addition of the application system, the growing variety of databases, here are four solutions to ensure that data is not lost in case of failure or catastrophic situation: The 1st solution is to use data backup hard disk or any other devices which able to do same functions. This way costs lowest price, but strongest preservation, deficiency is in time backup. The 2nd solution is to use a local disk arrays were every server's local disk data redundancy. 3rd option is to use fault tolerance mode, the two machines mutual backup systems, this way is used to solve the single failure and downtime, in case to prevent a single hard drive data loss caused by the fault, but the larger upfront investment. The 4th approach is using centralized SAN or NAS storage area of each server, a high-level data backup disk hardware failure, but the cost is high, generally cannot prevent failure of the system layer, such as a virus or system crashes.The non-authenticated user on the network may attempt to bypass the system conditions, such as physically remove data in database, wiretapping on some important communication line interception. For such threats, the most effective solution is to encrypt the data that is store and transmit in an encrypted format including sensitive data. The sender use an encryption key, encryption algorithm or device to encrypt data and then send to the recipient. Recipient receiving the cipher text and using the decryption key to decrypt cipher text to plaintext. If someone steals data under the transmission, he can only get unintelligible cipher text, and thus confidential information play the role.On the other hand, if the data is or will be stored in the cloud, then the overall security architecture should be a major concern in a compatible cloud platform security tool. For example, many NGFW support virtual firewall to the cloud platform compatible. Similarly, the network security measures should also focus on the use of secure Web gateway (SWG) and malware sandboxing to prevent loss of data between networks. In addition, these tools can limit potential breeding malware data between the enterprise network, various cloud service providers and Internet transmission. Many SWG andmalware sandbox provides cloud services, so they are more suitable for those companies to store data in the cloud.Management level is the important part of Network security concern. Unclear responsibilities and Competences, which is a sign of not good safety management system, there is lack of manoeuvrability so may cause risks of management security. When the network is under attack list or some other common network security threats like: (illegal operations such as internal people, etc.), those things cannot be real-time detected, therefore monitoring of system, reporting of error and early warning to the user will be delayed. Meanwhile, when the accidental action occurred, it cannot helps to keep the evident which means hard to provide clues so that could be able to track hacker attacks and helps to solve these case on the basis of behaviour, namely the lack of network controllability or auditability. These alarmed us to record visiting activities for the sites to detect all illegal intrusion.In many respects, the identification of cyber risks is a relatively straightforward task. Almost all Internet risks spring from one or more of three sources:•Variable reliability and application of technology;•Uncertainty surrounding legal and regulatory compliance issues; •Problematic behaviour of personnel in employing and operating Internet technologies.These types of concern tend not to arise so critically in traditional business and professional environments where procedures are well established, codes and protocols govern business and professional conduct, and models and channels for providing goods and services are conventional.Internet technologies are disruptive. They introduce new models for the provision of goods and services based on a global platform and in an environment where communications are instantaneous, paper records are subsumed in digital content, and speed, efficiency and cost-effectiveness are paramount.In such a challenging environment, risks abound and are not always easy to identify. In fact, the risks are so numerous, it is virtually impossible to assemble a comprehensive catalogue of Internet risks, not least because they differ from organisation to organisation – and what may be a risk for one concern may present no problem to another.For effectively managing the cyber risks required basic understanding of assessment the impacts of risks. A strategy for management of risks should be corresponded with nature and degree of the risk to be addressed. Risk assessment tries to identify and anticipate possible events. To be an effective risk assessment could offer an organisation that the opportunities to take better control of both its internal and external environment. Instead of just reacting to events, while organisation could come with an effective risk assessment system and a good management strategy, these things can helps to plan its every actions with better confidence that it will not be undermined by unforeseen events.Risk assessment involves certain processes. The first is to identify the risks associated with a particular activity or strategy. Technological, legal compliance and operational risks were identified in earlier chapters. The next process is to assess and evaluate the potential impact of a particular risk on the organisation. The third process involves implementing appropriate steps to either eliminate the risk or reduce it to an acceptable level, namely risk managementRisk management principlesIn order to approach a good risk management system five keys should be take care of:First requirement is a decision making by getting a disciplined approach. Which must be able to have comprehensive understands the scopes, functions and limitation that strategy to be pursued.Secondly, there is also necessary to have awareness as culture that risk is existed and cannot be ignored. Senior management has created an organisation’s culture for that, therefore, an awareness culture such as responsibility for the development and management in an enterprise in needed.Thirdly, that is important to develop the skills in weighing risk and potential opportunity. Encryption technology may involve considerable resources in terms of staff training and the cost of technology. However, if properly managed, the strategy will more than pay for itself if corporate clients are attracted through a perception that the organisation is sensitive to consumer concerns over security and adopts a modern approach to its use of information technology.Fourth, that is needed for an understanding of the wider implications and managing the strategy – an appreciation of the risk that may be spread out, or a mix of approaches that implementation might involve. This is particularly appropriate for Internet risks, where the risks arise from a variety of areas and where management solutions may be needed for these different risk areas simultaneously.Fifth, that is important to appreciate the changing environment, so that the organisation should be handled changes when they are occurring. New technology solutions emerge with great frequency. Each solution may have management implications in terms of new functions required of personnel and possibly the emergence of new legal compliance risks.。
第四次工业革命的优缺点英文作文全文共3篇示例，供读者参考篇1The Fourth Industrial Revolution: Advantages and DisadvantagesThe Fourth Industrial Revolution, characterized by the fusion of technologies bridging the physical, digital, and biological worlds, has brought about unprecedented changes in society, economy, and culture. As with any major shift, there are both advantages and disadvantages associated with this revolution.Advantages:1. Increased Efficiency: The adoption of automation, artificial intelligence, and Internet of Things (IoT) technologies has significantly improved efficiency in various industries. This has led to faster production processes, reduced costs, and increased productivity.2. Improved Connectivity: The Fourth Industrial Revolution has interconnected people, devices, and systems like never before. This has facilitated communication, collaboration, andinformation sharing on a global scale, leading to increased innovation and creativity.3. Enhanced Customer Experience: With the rise of data analytics and personalized marketing, businesses can now better understand and cater to the needs of their customers. This has led to improved customer satisfaction and loyalty.4. Job Creation: While automation has led to the displacement of some jobs, it has also created new opportunities in emerging industries such as artificial intelligence, robotics, and biotechnology. The Fourth Industrial Revolution has the potential to create millions of new jobs in the coming years.5. Sustainable Development: The integration of green technologies and sustainable practices in industries has the potential to address pressing environmental issues such as climate change and resource depletion. This can lead to a more sustainable and eco-friendly future.Disadvantages:1. Job Displacement: Automation and artificial intelligence have led to the displacement of millions of jobs in traditional industries such as manufacturing and retail. This has resulted inunemployment, underemployment, and income inequality in many countries.2. Data Privacy Concerns: The Fourth Industrial Revolution has brought about an explosion of data collection and analysis. This has raised concerns about data privacy, security, and surveillance, as well as the potential misuse of personal information by corporations and governments.3. Digital Divide: The increasing reliance on digital technologies in the Fourth Industrial Revolution has widened the gap between those who have access to these technologies and those who do not. This digital divide can further marginalize disadvantaged communities and exacerbate existing inequalities.4. Technological Dependence: As society becomes more reliant on digital technologies, there is a risk of overdependence and vulnerability to technological failures, cyber attacks, and other disruptions. This can pose significant risks to critical systems and infrastructure.5. Ethical Dilemmas: The use of advanced technologies such as artificial intelligence, genetic engineering, and biotechnology raises ethical concerns about issues such as data privacy, autonomous weapons, human enhancement, and the impact onsociety and culture. These ethical dilemmas need to be addressed to ensure responsible and ethical use of technology.In conclusion, the Fourth Industrial Revolution presents both opportunities and challenges for society. It is essential to harness the benefits of this revolution while mitigating its negative impacts. By addressing the disadvantages and promoting responsible innovation, we can create a more inclusive, sustainable, and prosperous future for all.篇2The Fourth Industrial Revolution, also known as Industry 4.0, is characterized by the fusion of technologies that blur the lines between the physical, digital, and biological spheres. This revolution is changing the way we live, work, and interact with the world around us. As with any major shift in society, there are both advantages and disadvantages to the Fourth Industrial Revolution.One of the biggest advantages of the Fourth Industrial Revolution is the increased efficiency and productivity it brings to various industries. Automation, artificial intelligence, and the Internet of Things are revolutionizing the way businesses operate, leading to faster production times, higher qualityproducts, and lower costs. This has the potential to improve global economic growth and create new job opportunities in high-tech fields.Another advantage of Industry 4.0 is the potential to address pressing global challenges such as climate change, resource scarcity, and healthcare. Smart technologies can help us monitor and reduce energy consumption, improve resource efficiency, and provide personalized healthcare solutions. By harnessing the power of data and technology, we can create a more sustainable and inclusive future for all.However, the Fourth Industrial Revolution also comes with its fair share of challenges. One of the main concerns is the impact of automation on the job market. As machines become more intelligent and capable of performing tasks traditionally done by humans, there is a risk of widespread unemployment and income inequality. It is crucial for policymakers and companies to invest in reskilling and upskilling programs to ensure that workers are prepared for the jobs of the future.Additionally, there are ethical considerations that come with the rise of Industry 4.0. As artificial intelligence becomes more sophisticated, there are concerns about data privacy, surveillance, and the potential for bias in decision-making processes. It isimportant for companies to prioritize ethical principles and ensure that technology is used for the greater good of society.In conclusion, the Fourth Industrial Revolution has the potential to bring about transformative changes to society, but it is important to address the challenges and risks that come with it. By investing in education, training, and ethical frameworks, we can harness the power of technology to create a more sustainable and inclusive future for all.篇3The Fourth Industrial Revolution, often referred to as Industry 4.0, is the current wave of technological advancements that are changing the way we live, work, and interact with each other. This revolution is characterized by the integration of digital technologies, artificial intelligence, automation, and the Internet of Things into traditional industries, leading to increased efficiency, productivity, and connectivity.Advantages of the Fourth Industrial Revolution:1. Increased Efficiency: One of the key advantages of the Fourth Industrial Revolution is the increased efficiency it brings to industries. Automation and artificial intelligence technologiescan streamline processes, reduce human error, and make operations more cost-effective.2. Improved Productivity: With the use of advanced technologies such as robotics and machine learning, companies can increase their output and productivity levels. This leads to faster production cycles and higher profitability.3. Enhanced Connectivity: The Fourth Industrial Revolution has made it easier for businesses to connect with customers, suppliers, and partners around the world. The Internet of Things allows for real-time data exchange, leading to betterdecision-making and collaboration.4. Innovation and Creativity: Industry 4.0 encourages innovation and creativity, as companies strive to stay ahead of the competition by adopting new technologies and business models. This can lead to the development of new products and services that meet the evolving needs of consumers.5. Job Creation: While there are concerns about job losses due to automation, the Fourth Industrial Revolution also has the potential to create new roles and opportunities for skilled workers. As industries evolve, there will be a growing demand for professionals with expertise in digital technologies, data analytics, and cybersecurity.Disadvantages of the Fourth Industrial Revolution:1. Job Displacement: One of the biggest concerns surrounding Industry 4.0 is the potential for job displacement. As more tasks become automated, there is a risk that many workers will be replaced by machines, leading to unemployment and economic instability.2. Skills Gap: The rapid pace of technological change in the Fourth Industrial Revolution means that many workers may not have the skills or training needed to adapt to new roles. This can result in a widening skills gap, with a lack of qualified workers in key industries.3. Data Security and Privacy Concerns: The use of digital technologies in Industry4.0 raises concerns about data security and privacy. With increased connectivity and data exchange, there is a risk of cyberattacks, data breaches, and unauthorized access to sensitive information.4. Environmental Impact: While Industry 4.0 can lead to increased efficiency and productivity, it also has the potential to have a negative impact on the environment. The manufacturing and operation of digital technologies can contribute to pollution, resource depletion, and carbon emissions.5. Social Inequality: The benefits of the Fourth Industrial Revolution are not distributed equally, leading to increased social inequality. Those with access to advanced technologies and digital skills are more likely to succeed, while others may be left behind, exacerbating existing disparities.In conclusion, the Fourth Industrial Revolution has the potential to bring significant benefits to industries and societies, but it also poses challenges that need to be addressed. It is important for policymakers, businesses, and individuals to work together to ensure that the advantages of Industry 4.0 are maximized, while mitigating its negative impacts. By investing in education and training, adopting ethical standards for data use, and promoting sustainable practices, we can harness the power of technology for the greater good.。
Database Security“Why do I need to secure my database server? No one can access it —it’s in a DMZ protected by the firewall!” This is often the response when it is recommended that such devices are included within a security health check. In fact, database security is paramount in defending an organizations information, as it may be indirectly exposed to a wider audience than realized.This is the first of two articles that will examine database security. In this article we will discuss general database security concepts and common problems. In the next article we will focus on specific Microsoft SQL and Oracle security concerns.Database security has become a hot topic in recent times. With more and more people becoming increasingly concerned with computer security, we are finding that firewalls and Web servers are being secured more than ever(though this does not mean that there are not still a large number of insecure networks out there). As such, the focus is expanding to consider technologies such as databases with a more critical eye.◆Common sense securityBefore we discuss the issues relating to database security it is prudent to high- light the necessity to secure the underlying operating system and supporting technologies. It is not worth spending a lot of effort securing a database if a vanilla operating system is failing to provide a secure basis for the hardening of the data- base. There are a large number of excellent documents in the public domain detailing measures that should be employed when installing various operating systems.One common problem that is often encountered is the existence of a database on the same server as a web server hosting an Internet (or Intranet) facing application. Whilst this may save the cost of purchasing a separate server, it does seriously affect the security of the solution. Where this is identified, it is often the case that the database is openly connected to the Internet. One recent example I can recall is an Apache Web server serving an organizations Internet offering, with an Oracle database available on the Internet on port 1521. When investigating this issue further it was discovered that access to the Oracle server was not protected (including lack of passwords), which allowed the server to be stopped. The database was not required from an Internet facing perspective, but the use of default settings and careless security measures rendered the server vulnerable.The points mentioned above are not strictly database issues, and could be classified as architectural and firewall protection issues also, but ultimately it is the database that is compromised. Security considerations have to be made from all parts of a public facing net- work. You cannot rely on someone or something else within your organization protecting your database fr om exposur e.◆ Attack tools are now available for exploiting weaknesses in SQL and OracleI came across one interesting aspect of database security recently while carrying out a security review for a client. We were performing a test against an intranet application, which used a database back end (SQL) to store client details. The security review was proceeding well, with access controls being based on Windows authentication. Only authenticated Windows users were able to see data belonging to them. The application itself seemed to be handling input requests, rejecting all attempts to access the data- base directly.We then happened to come across a backup of the application in the office in which we were working. This media contained a backup of the SQL database, which we restored onto our laptop. All security controls which were in place originally were not restored with the database and we were able to browse the complete database, with no restrictions in place to protect the sensitive data. This may seem like a contrived way of compromising the security of the system, but does highlight an important point. It is often not the direct approach that is taken to attack a target, and ultimately the endpoint is the same; system compromise. A backup copy of the database may be stored on the server, and thus facilitates access to the data indirectly.There is a simple solution to the problem identified above. SQL 2000 can be configured to use password protection for backups. If the backup is created with password protection, this password must be used when restoring the password. This is an effective and uncomplicated method of stopping simple capture of backup data. It does however mean that the password must be remembered!◆Curr ent tr endsThere are a number of current trends in IT security, with a number of these being linked to database security.The focus on database security is now attracting the attention of the attackers. Attack tools are now available for exploiting weaknesses in SQL and Oracle. The emergence of these tools has raised the stakes and we have seen focused attacks against specific data- base ports on servers exposed to the Internet.One common theme running through the security industry is the focus on application security, and in particular bespoke Web applications. With he functionality of Web applications becoming more and more complex, it brings the potential for more security weaknesses in bespoke application code. In order to fulfill the functionality of applications, the backend data stores are commonly being used to format the content of Web pages. This requires more complex coding at the application end. With developers using different styles in code development, some of which are not as security conscious as other, this can be the source of exploitable errors.SQL injection is one such hot topic within the IT security industry at the moment. Discussions are now commonplace among technical security forums, with more and more ways and means of exploiting databases coming to light all the time. SQL injection is a misleading term, as the concept applies to other databases, including Oracle, DB2 and Sybase.◆ What is SQL Injection?SQL Injection is simply the method of communication with a database using code or commands sent via a method or application not intended by the developer. The most common form of this is found in Web applications. Any user input that is handled by the application is a common source of attack. One simple example of mishandling of user input is highlighted in Figure 1.Many of you will have seen this common error message when accessing web sites, and often indicates that the user input has not been correctly handled. On getting this type of error, an attacker will focus in with more specific input strings.Specific security-related coding techniques should be added to coding standard in use within your organization. The damage done by this type of vulnerability can be far reaching, though this depends on the level of privileges the application has in relation to the database.If the application is accessing data with full administrator type privileges, then maliciously run commands will also pick up this level of access, and system compromise is inevitable. Again this issue is analogous to operating system security principles, where programs should only be run with the minimum of permissions that is required. If normal user access is acceptable, then apply this restriction.Again the problem of SQL security is not totally a database issue. Specific database command or requests should not be allowed to pass through theapplication layer. This can be prevented by employing a “secure coding” approach.Again this is veering off-topic, but it is worth detailing a few basic steps that should be employed.The first step in securing any application should be the validation and control of user input. Strict typing should be used where possible to control specific data (e.g. if numeric data is expected), and where string based data is required, specific non alphanumeric characters should be prohibited where possible. Where this cannot be performed, consideration should be made to try and substitute characters (for example the use of single quotes, which are commonly used in SQL commands).Specific security-related coding techniques should be added to coding standard in use within your organization. If all developers are using the same baseline standards, with specific security measures, this will reduce the risk of SQL injection compromises.Another simple method that can be employed is to remove all procedures within the database that are not required. This restricts the extent that unwanted or superfluous aspects of the database could be maliciously used. This is analogous to removing unwanted services on an operating system, which is common security practice.◆ OverallIn conclusion, most of the points I have made above are common sense security concepts, and are not specific to databases. However all of these points DO apply to databases and if these basic security measures are employed, the security of your database will be greatly improved.The next article on database security will focus on specific SQL and Oracle security problems, with detailed examples and advice for DBAs and developers.There are a lot of similarities between database security and general IT security, with generic simple security steps and measures that can be (and should be) easily implemented to dramatically improve security. While these may seem like common sense, it is surprising how many times we have seen that common security measures are not implemented and so causea security exposure.◆User account and password securityOne of the basic first principals in IT security is “make su re you have a good password”. Within this statement I have assumed that a password is set in the first place, though this is often not the case.I touched on common sense security in my last article, but I think it is important to highlight this again. As with operating systems, the focus of attention within database account security is aimed at administrationaccounts. Within SQL this will be the SA account and within Oracle it may be the SYSDBA or ORACLE account.It is very common for SQL SA accounts to have a password of ‘SA’ or even worse a blank password, which is just as common. This password laziness breaks the most basic security principals, and should be stamped down on. Users would not be allowed to have a blank password on their own domain account, so why should valuable system resources such as databases be allowed to be left unprotected. For instance, a blank ‘SA’password will enable any user with client software (i.e. Microsoft query analyser or enterprise manager to ‘manage’ the SQL server and databases).With databases being used as the back end to Web applications, the lack of password control can result in a total compromise of sensitive information. With system level access to the database it is possible not only to execute queries into the database, create/modify/delete tables etc, but also to execute what are known as Stored Procedures.数据库安全“为什么要确保数据库服务安全呢？任何人都不能访问-这是一个非军事区的保护防火墙”，当我们被建议使用一个带有安全检查机制的装置时，这是通常的反应。
information services department can do it.1）后备技术Back-up technology由于现代计算机科学技术的快速发展，以往的数据备份已经不能满足用户和管理者对现有系统的要求，现在的技术一般是进行系统数据库的实时备份和备份服务器。
当数据库瘫痪时，通过快速进行系统库的切换，这样可以有效的减少数据的丢失。
当用户量大时，也可以使用备用服务器，两个服务器进行同步数据存储，如果一台服务器出错时，可以转换到另一台进行相同的操作，让用户不需要因瘫痪而面临网页打不开、数据丢失等相关问题。
Due to the rapid development of modern computer science and technology, previous data backup and managers have been unable to meet the user requirements of the existing system, and now the technology is generally carried out in real-time backup system database and backup servers. When the database is paralyzed by rapidly switching system libraries, which can effectively reduce the loss of data. When the user capacity, you can use the backup server, two servers synchronize data storage, if a server error, can be converted to another the same operation, so that the user does not open the page because of paralysis of face , data loss and other related issues.2）降效技术Drop-efficient technology通常情况下系统的管理员都不是专业的计算机人员，对计算机专业的知识了解相对较少。
半导体db工艺英文自我介绍My name is [Your Name], and I am a highly experienced and skilled Database Engineer with a proven track record of success in the semiconductor industry. I have over 10 years of experience in designing, developing, and maintaining complex database systems for various applications,including chip design, manufacturing, and testing.Throughout my career, I have consistently exceeded expectations in delivering high-quality database solutions that meet the demanding requirements of the semiconductor industry. I am proficient in a wide range of database technologies, including Oracle, PostgreSQL, MySQL, and MongoDB. I also have a deep understanding of data modeling, query optimization, and database performance tuning.In my previous role at [Previous Company Name], I was responsible for the design and implementation of a comprehensive database system to support the entire chip design process. I led a team of engineers in developing ascalable and reliable database that could handle massive volumes of data and complex queries. The system we developed significantly improved the efficiency and productivity of the design team, enabling them to reduce design cycles and accelerate product development.I have also played a key role in developing and implementing database solutions for semiconductor manufacturing. At [Previous Company Name], I designed and implemented a real-time database system to monitor and control the manufacturing process. The system providedreal-time visibility into the production line, allowing engineers to quickly identify and resolve any issues that could impact yield or quality. This system significantly improved manufacturing efficiency and reduced production costs.In addition to my technical skills, I am also an effective communicator and team player. I have a proven ability to work closely with stakeholders, including engineers, scientists, and business leaders, to understand their requirements and deliver solutions that meet theirneeds. I am also comfortable presenting technical information to both technical and non-technical audiences.I am eager to join your team and contribute my skills and experience to the success of your company. I am confident that I can make a significant contribution to your organization by delivering high-quality database solutions that meet the demanding requirements of the semiconductor industry.Thank you for your time and consideration. I look forward to the opportunity to discuss my qualifications further and demonstrate how I can be a valuable asset to your team.。
linux rsync校验方法1. rsync命令用于在Linux系统上同步文件和目录。
The rsync command is used to synchronize files and directories on Linux systems.2. rsync可以通过网络连接远程主机来同步文件，也可以在本地计算机之间进行同步。
rsync can synchronize files by connecting to remote hosts over the network, or between local computers.3. rsync能够快速地同步大量数据，只传输发生变化的部分，节省带宽和时间。
rsync can quickly synchronize large amounts of data, only transferring the changed parts, saving bandwidth and time.4.在使用rsync进行文件同步时，可以选择校验文件内容以确保数据的完整性。
When using rsync for file synchronization, you can choose to verify file contents to ensure data integrity.5. rsync提供了多种校验方法，可以根据实际需要选择合适的方式。
rsync offers multiple verification methods, allowing you to choose the appropriate method based on your needs.6.一种常见的校验方法是使用MD5校验和，对文件内容进行哈希计算并进行比对。
One common verification method is to use MD5 checksums, calculating hashes of file contents and comparing them.7.使用MD5校验和可以检测文件内容是否被篡改，确保同步后的文件与源文件一致。
real_time的指标Real-time metrics are crucial for businesses in today's fast-paced and competitive environment. These metrics provide real-time insights into various aspects of a business, allowing for quick decision-making and effective response to changing market conditions. From a business perspective, real-time metrics offer several advantages.Firstly, real-time metrics enable businesses to monitor and track their performance in real-time. This allows for immediate identification of any issues or deviations from the desired targets, enabling prompt corrective actions. For example, if a company notices a sudden drop in website traffic, it can quickly investigate the cause and take necessary steps to rectify the situation, such as optimizing the website or launching a targeted marketing campaign.Secondly, real-time metrics help businesses stay ahead of the competition. By constantly monitoring keyperformance indicators (KPIs) in real-time, companies can identify emerging trends, market shifts, and customer preferences faster than their competitors. This allows for agile decision-making and the ability to adapt strategies accordingly. For instance, an e-commerce company that tracks real-time sales data can quickly identify which products are performing well and adjust its inventory or marketing efforts to capitalize on the trend.Moreover, real-time metrics provide businesses with valuable insights into customer behavior and preferences. By analyzing real-time data from various sources such as social media, website analytics, and customer feedback, companies can gain a deeper understanding of their target audience. This helps in tailoring products, services, and marketing campaigns to better meet customer needs and expectations. For example, a retail store that monitors real-time customer feedback on social media can quickly address any negative experiences and improve overall customer satisfaction.Real-time metrics also play a crucial role in riskmanagement and fraud detection. By monitoring real-time data, businesses can detect anomalies or suspicious activities promptly. This is particularly important in industries such as finance and cybersecurity, where immediate action is required to prevent potential losses or breaches. For instance, a bank that tracks real-time transaction data can quickly identify any unusual patterns or fraudulent activities and take appropriate measures to mitigate the risks.Furthermore, real-time metrics facilitate effective resource allocation and optimization. By continuously monitoring resource utilization and performance metrics in real-time, businesses can identify areas of inefficiency or underutilization. This allows for timely adjustments in resource allocation, leading to cost savings and improved operational efficiency. For example, a manufacturing company that tracks real-time production data can identify bottlenecks or equipment failures and take immediate action to minimize downtime and maximize productivity.Lastly, real-time metrics enhance transparency andaccountability within an organization. By making real-time data accessible to relevant stakeholders, businesses foster a culture of data-driven decision-making and encourage individual and team accountability. This promotes a proactive approach to problem-solving and empowers employees to take ownership of their performance. For instance, a sales team that has access to real-time sales data can track their progress, identify areas for improvement, and take necessary actions to achieve their targets.In conclusion, real-time metrics offer numerousbenefits to businesses. They enable organizations to monitor performance, stay ahead of the competition, understand customer behavior, manage risks, optimize resources, and foster transparency and accountability. By leveraging real-time data, businesses can make informed decisions, respond promptly to market changes, and drive growth and success in today's dynamic business landscape.。
操作系统概念第七版答案【篇一：操作系统概念第七版答案(含编程代码)】> chapter 11.1 in a multiprogramming and time-sharing environment, several users share the system simultaneously. this situation can result in various security problems. a. what are two such problems?b. can we ensure the same degree of security in a time-shared machine as in a dedicated machine? explain your answer.answer:a. stealing or copying one’s programs or data; using system resources (cpu, memory, disk space, peripherals) without proper accounting.b. probably not, since any protection scheme devised by humans can inevitably be broken by a human, and the more complex the scheme, the more difficult it is to feel confident of its correct implementation.1.2 the issue of resource utilization shows up in different forms in different types of operating systems. list what resources must be managedcarefully in the following settings: a. mainframe or minicomputer systems b. workstations connected to serversc. handheld computersanswer:a. mainframes:memory and cpu resources, storage, network bandwidth.b. workstations: memory and cpu resoucesc. handheld computers: power consumption, memory resources.1.3 under what circumstances would a user be better off using a timesharing system rather than a pc or single-user workstation?answer: when there are few other users, the task is large, and the hardware is fast, time-sharingmakes sense. the full power of the system can be brought to bear on the user’s problem. the problemcan be solved faster than on a personal computer. another case occurs when lots of other users need resources at the same time.a personal computer is best when the job is small enough to be executed reasonably on it and when performance is sufficient to execute the prog ram to the user’s satisfaction.1.4 which of the functionalities listed below need to be supported by the operating system for the following two settings: (a) handheld devices and (b) real-time systems. a. batch programmingb. virtual memoryc. time sharinganswer: for real-time systems, the operating system needs to support virtual memoryand time sharing in a fair manner. for handheld systems,the operating system needs to provide virtual memory, but does not need to provide time-sharing. batch programming is not necessary in both settings.1.5 describe the differences between symmetric and asymmetric multiprocessing.what are three advantages and one disadvantage of multiprocessor systems?answer: symmetric multiprocessing treats all processors as equals, and i/o can be processed on any cpu. asymmetric multiprocessing has one master cpu and the remainder cpus are slaves. the master distributes tasks among the slaves, and i/o is usually done by the master only.multiprocessors can save money by not duplicating power supplies,housings, and peripherals. they can execute programs more quickly and can have increased reliability. they are also more complex in both hardware and software than uniprocessor systems.1.6 how do clustered systems differ from multiprocessor systems? what is required for two machines belonging to a cluster to cooperate to provide a highly available service?answer: clustered systems are typically constructed by combining multiple computers into a single system to perform a computational task distributed across the cluster. multiprocessor systems on the other hand could be a single physical entity comprising of multiple cpus. a clustered system is less tightly coupled than a multiprocessorsystem.clustered systems communicate using messages, while processors in a multiprocessor system could communicate using shared memory.in order for twomachines to provide a highly available service, the state on the two machines should be replicated and shouldbe consistently updated. when one of the machines fail, the other could then take-over the functionality of the failed machine.1.7 distinguish between the client-server and peer-to-peer models of distributed systems.answer: the client-server model firmly distinguishes the roles of the client and server. under this model, the client requests services that are provided by the server. the peer-to-peer model doesn’t have such strict roles. in fact, all nodes in the system are considered peers and thus may act as either clients or servers - or both. a node may request a service from another peer, or the node may in fact provide such a service to other peers in the system.for example, let’s consider a system of nodes tha t share cooking recipes.under the client-server model, all recipes are stored with the server. if a client wishes to access a recipe, it must request the recipe from the specified server. using the peer-to-peer model, a peer node could ask other peer nodesfor the specified recipe.the node (or perhaps nodes) with the requested recipe could provide it to the requesting node. notice how each peer may act as both a client (i.e. it may request recipes) and as a server (it may provide recipes.)1.8 consider a computing cluster consisting of twonodes running adatabase.describe two ways in which the cluster software can manage access to the data on the disk. discuss the benefits and disadvantages of each.answer: consider the following two alternatives: asymmetric clustering and parallel clustering. with asymmetric clustering, one host runs the database application with the other host simply monitoring it. if the server fails, the monitoring host becomes the active server. this is appropriate for providing redundancy. however, it does not utilize the potential processing power of both hosts. with parallel clustering, the database application can run in parallel on both hosts. the difficulty implementing parallel clusters is providing some form of distributed locking mechanism for files on the shared disk.1.9 how are network computers different from traditional personal computers? describe some usage scenarios in which it is advantageous to use network computers.answer: a network computer relies on a centralized computer for most of its services. it can therefore have a minimal operating system to manage its resources. a personal computer on the other hand has to be capable of providing all of the required functionality in a standalonemanner without relying on a centralized manner. scenarios where administrative costs are high and where sharing leads to more efficient use of resources are precisely those settings where network computers are preferred.1.10 what is the purpose of interrupts? what are the differences between a trap and an interrupt? can traps be generated intentionally by a user program? if so, for what purpose?answer: an interrupt is a hardware-generated change-of-flow within the system. an interrupt handler is summoned to deal with the cause of the interrupt; control is then returned to the interrupted context and instruction. a trap is a software-generated interrupt. an interrupt can be used to signal the completion of an i/o to obviate the need for device polling. a trap can be used to call operating system routines or to catch arithmetic errors.1.11 direct memory access is used for high-speed i/o devices in order to avoid increasing the cpu′s execution load.a. how does the cpu interface with the device to coordinate the transfer?b. how does the cpu know when the memory operations are complete?c. the cpu is allowed to execute other programs while the dma controller istransferring data. does this process interfere with the execution of the user programs? if so, describe what forms of interference are caused.answer: the cpu can initiate a dma operation by writing values into special registers that can be independently accessed by the device.the device initiates the corresponding operation once it receives a command from the cpu. when the device is finished with its operation, it interrupts the cpu to indicate the completion of the operation.both the device and the cpu can be accessing memory simultaneously.the memory controller provides access to the memory bus in a fair manner to these two entities.a cpu might therefore be unable to issue memory operationsat peak speeds since it has to compete with the device in order to obtain access to the memory bus.answer: an operating system for a machine of this type would need to remain in control (or monitor mode) at all times. this could be accomplished by two methods:a. software interpretation of all user programs (like some basic,java, and lisp systems, for example). the software interpreter would provide, in software, what the hardware does not provide.b. require meant that all programs be written in high-level languages so that all object code is compiler-produced. the compiler would generate (either in-line or by function calls) the protection checks that the hardware is missing.1.13 give two reasons why caches are useful.what problems do they solve? what problems do they cause? if a cache canbe made as large as the device for which it is caching (for instance, a cache as large as a disk), why not make it that large and eliminate the device?answer: caches are useful when two or more components need to exchange data, and the components perform transfers at differing speeds.caches solve the transfer problem by providing a buffer of intermediate speed between the components. if the fast device finds the data it needs in the cache, it need not wait for the slower device. the data in the cache must be kept consistent with the data in the components. if a omponent has a data value change, and the datum is also in the cache, the cache must also be updated. this is especially a problem on multiprocessor systemswhere more than one process may be accessing adatum.acomponent may be eliminated by an equal-sized cache, but only if: (a) the cache and the component have equivalent state-saving capacity (that is,if the component retains its data when electricity is removed, the cache must retain data as well), and (b) the cache is affordable, because faster storage tends to be more expensive.1.14 discuss, with examples, how the problem of maintaining coherence of cached data manifests itself in the following processing environments:a. single-processor systemsb. multiprocessor systemsc. distributed systemsanswer: in single-processor systems, the memory needs tobe updated when a processor issues updates to cached values. these updates can be performed immediately or in a lazy manner. in amultiprocessor system,different processors might be caching the same memory location in its local caches. when updates are made, the other cached locations need to be invalidated or updated. in distributed systems, consistency of cached memory values is not an issue. however, consistency problems might arise when a client caches file data.1.15 describe a mechanism for enforcing memory protectionin order to prevent a program from modifying the memory associated with other programs.answer: the processor could keep track of what locations are associated with each process and limit access to locationsthat are outside of a program’s extent. informatio n regarding the extent of a program’s memory could be maintained by using base and limits registers and by performing a check for every memory access.1.16 what network configuration would best suit the following environments? a. a dormitory floorb. a university campusc. a stated. a nationanswer:a. a dormitory floor - a lan.b. a university campus - a lan, possible a wan for very large campuses.c. a state - awan.d. a nation - a wan.1.17 define the essential properties of the following types of operating systems: a. batchb. interactivec. time sharingd. real timee. networkf. parallelg. distributedh. clusteredi. handheld【篇二：操作系统概念第七版4-6章课后题答案(中文版)】举两个多线程程序设计的例子来说明多线程不比单线程方案提高性能答：1）任何形式的顺序程序对线程来说都不是一个好的形式。
英文文献及翻译(计算机专业)The increasing complexity of design resources in a net-based collaborative XXX common systems。
design resources can be organized in n with design activities。
A task is formed by a set of activities and resources linked by logical ns。
XXX managementof all design resources and activities via a Task Management System (TMS)。
which is designed to break down tasks and assign resources to task nodes。
This XXX。
2 Task Management System (TMS)TMS is a system designed to manage the tasks and resources involved in a design project。
It poses tasks into smaller subtasks。
XXX management of all design resources and activities。
TMS assigns resources to task nodes。
XXX。
3 Collaborative DesignCollaborative design is a process that XXX a common goal。
In a net-based collaborative design environment。
n XXX n for all design resources and activities。
Chapter ThreeOPERATING SYSTEMSChapter SummaryThis chapter introduces the fundamental concepts associated with operating systems. It begins with a historical look at operating systems, followed by discussions of operating system architecture and internal operation. An optional section covers semaphores and deadlock. The chapter closes with a discussion of security issues.Comments1. This chapter provides an excellent opportunity to introduce the particular features of the local operating system (e.g. pertinent issues of file management, any sign-on and sign-off procedures, and perhaps e-mail features), and the utility programs (such as the editor) that will be used later in this or other classes.2. The image I like to convey to the student is that of the operating system residing between the computer user and the hardware. Once this image is established, it's nice to show how different operating systems can produce different personalities from essentially the same hardware technology. One method of doing this is to compare an icon-based windowing system with a text oriented system.3. An operating system is an important example of a large software system, and thus this chapter provides an opportunity to set the stage for software engineering in Chapter 7. This is one reason why the modular structure of an operating system is presented in this chapter. Time spent in class on this topic can pay dividends in the form of ready examples and a basis for class discussions when covering Chapter 7—not to mention the fact that it reinforces the organized, modular approach to problem solving that we want our students to appreciate.4. Don’t miss the opportunities to reinforce the concept of abstraction and abstract tools while covering this chapter.5. A point that many students never stop to consider is that the operating system is itself a program that is being executed on the same machine that it is controlling. In particular, such components as the command processor, file manager, or scheduler must essentially share time with the other processes in the system. Pointing this out to a beginning class increases the complexity of a classroom discussion but has the advantage of conveying the true complexity of a multiprogramming operating system.Answers to Chapter Review Problems1. Control data and its access, provide for efficient device access, coordinate the use of the machine's resources, and control access to the machine.2. Batch processing refers to the process of collecting a program (or programs) together with data and submitting this material to the operating system for execution (perhaps at a later time) without further intervention by the user.Interactive processing refers to the technique of executing a program in a manner that allows the user to communicate with the program during its execution.3. R, S, T, X, Y, Z (The items are removed in the same order they were placed in the queue.)4. Interactive processing allows the user to communicate with a program during its execution. The phrase "real-time processing" means that the time required for the activities of the program being executed must coordinate with activities in the outside world.5. An operating system that allows several activities to execute "at the same time."6. Answers will vary. The goal is for students to "experience" multitasking so that it is real rather than theoretical. We wan them to connect material in the text with reality.7. Answers will vary. They should project an understanding that application software reflects the computer's application, whereas utility software forms part of the system's infrastructure.8. a. The shell of an operating system handles the communication with the operating system’s users.b. The kernel of an operating system performs the fundamental tasks of the system.9. X is a directory containing the subdirectory Y, which contains the subdirectory Z.10. A process is the execution of a program.11. The status of each process (ready, waiting) and the priority of each process.12. A process that is ready could make progress if given a time slice, but giving a time slice to a process that is waiting would merely waste time since it cannot progress until some event occurs. 13. Virtual memory is the memory space whose presence is merely simulated by swapping blocks of data back and forth between a disk and the memory actually present in the machine.14. To create a 1024MB (MiB) virtual memory using 2KB (KiB) pages would require 524,288 pages.15. If both processes merely need to read from the file, no conflicts will occur. However, if one of the processes is going to modify the file, them it should have exclusive access. (Such problems are discussed in Section 9.5 in the context of databases.)16. Application software performs tasks that are unique to the use of the particular computer system, whereas system software performs tasks that are required as the software infrastructure of any computer system.17. Load balancing refers to the task of keeping all the processors busy. Scaling has to do with dividing a task into subtasks that can be performed simultaneously.18. The machine begins by executing a program, called the bootstrap, at a predetermined location in memory. This program directs the machine to load a program (the operating system) from mass storage into main memory. The original program tells the machine to transfer its attention to the program just loaded.19. Since most of a computer's main memory is volatile, the operating system must be reloaded each time the machine is turned on.20. Answers will vary. Most PCs give the user the option of altering parameters before the booting process actually begins--usually by pressing the F1 key. The software controlling this procedure is part of the BIOS stored in the machine's ROM. Students who have floppy drives will hear the bootstrap routine look for the operating system there before trying the hard drive. They should all be able to hear the bootstrap routine reading the operating system from the hard drive.21. If the machine can execute 5 instructions in a microsecond, it can execute 5,000 instructions in a millisecond or 100,000 instructions in a 20 millisecond time slice. (The point is that a modern machine can do a lot in a single time slice.)22. The typist would be typing 5 characters per second, or one every 200 milliseconds. Thus, 10 time slices could be allocated during the 200 milliseconds between characters.23. At least half. This does not include the time required to actually transfer the data. 25 milliseconds = 25000 microseconds. Thus, 250,000 instructions could be executed during this time.24. Memory space, disk storage space, access to a printer, time slices, and access to files.25. The I/O-bound process. This allows the controllers to start with the I/O activities. Then the compute-bound process can run while the other is waiting for these slower activities to take place. As a general rule of thumb, priority should be given to the slower activity.26. A mix of I/O-bound and compute-bound processes will normally produce a higher throughput than a collection of processes with similar characteristics. For example, little is gained by allowing a collection of compute-bound processes to share time. In fact, such a collection will usually get done faster without the delays caused by switching repeatedly among the different processes in the collection. However, in the case of several I/O bound processes, it could be that the relative timing of the I/O requests would produce benefits in a multiprogramming environment.27. Save the current process' state;select another process from the process table;load that process' state;start the next time slice.28. A process’s state includes the values in the CPU’s registers (including the program counter) as well as the contents of its associated memory cells.29. If a process asks for service from a mass storage device, its time-slice will be terminated because the process must wait for the device to perform the requested operation before continuing.30. First: Interrupt signal occurs.Second: Machine completes its current instruction.Third: Machine saves the current program state.Fourth: Machine begins executing the interrupt routine.31. These questions are compatible with any operating system. The answers will vary. The goal is for the student to relate the material in the text to an actual operating system.32. These questions are intended for a multiuser, multitasking operating system such as UNIX. The answers will vary. The goal is for the student to relate the material in the text to an actual operating system.33. The test-and-set instruction is often used to implement semaphores. Since its task is executed asa single instruction, no interrupt signal can interfere.34. The banker has removed the competition for the nonshareable resource.35. Our approach to the problem is to consider permission from the instructor and the payment of the fee as nonshareable resources for which the students compete.a. This removes the competition for the nonshareable resources by removing the need for them.b. This removes the competition for nonshareable resources by adding additional resources (one more permission and one more fee payment privilege).c. Here the fee payment privilege and the instructor's permission are forcibly retrieved and given to another student.d. Here the instructor's permission is forcibly retrieved and given to the other student.36. The window manager forcibly retrieves an area of the screen that has been allocated to one process and reallocates it to another (by pushing a window into the background and bringing another to the foreground).37. Deadlock cannot occur because each process must request all the resources it will need at a certain level at once.38. First, one controlling computer reads the common cell and retrieves the value zero.Second, the other controlling computer reads the common cell and retrieves the value zero.Third, the first computer places a non-zero value in the common cell and tells its arm to pick up the assembly.Fourth, the other computer places a non-zero value in the common cell and tells its arm to pick up the assembly.39. As the processes producing the printed material terminate, their output that has accumulated in mass storage is placed in a queue to wait for the printer. Each time the printer finishes the output ofa process, it begins printing the next unit of output in this queue.40. a. The longer a lone car waits at a red light, the higher its priority becomes. Thus, it will ultimately be given a green light at the expense of the heavier traffic.b. The process whose time slice has just finished will most likely have the highest priority and therefore be awarded the next time slice. This is why dynamic priority systems are used in multiprogramming systems. That is, as a process waits for a time slice, its priority increases. (In the simplest cases, processes merely wait in a queue for the next time slice. Thus a process’ priority is reflected by its position in the queue. As each process completes a time slice, it is placed at the rear of the queue.)41. In both deadlock and starvation there are processes that are not able to make progress. The difference is that in the case of deadlock, none of the processes are able to execute, whereas in the case of starvation the higher priority processes are able to execute.42. The point of this problem is as much to introduce students to this piece of computer science folklore as it is to pose the problem itself. Issues include the problem of each philosopher obtaining possession of one fork as well as the problem of a philosopher's neighbors obtaining possession of the forks available to him and never releasing them.43. As the length of time slices become smaller, the ratio of time spent swapping processes compared to the time spent executing them increases. Thus, a point is reached where the efficiency of the system becomes quite low. On the other hand, if time slices are too long, the illusion of simultaneous operation is lost.44. Interrupt disable, interrupt enable, and the test-and-set instructions45. Answers may vary. Possibilities include establishing new accounts, removing accounts, establishing privileges, and monitoring the machine's usage.46. By loading the current process's memory limits in special purpose registers that the CPU uses to validate all references to main memory. If a reference is outside the bounds established by those registers, an interrupt will occur, causing control to be returned to the operating system.47. 269 milliseconds, which is many years. (The point is that milliseconds add up.)48. To allow the operating system the ability to protect processes from each other. The operating system runs in the highest privilege level but restricts the other processes to lower privilege levels. 49. Two that are identified in the text are changing the contents of memory limit registers and changing the CPU's current privilege level.50. Answers will vary. Possibilities include accessing data in memory cells outside the process's allocated space, gaining unauthorized access to mass storage, and modifying the operating system itself to gain advantage over other processes.。
Oracle® Database VaultRelease Notes10g Release 2 (10.2.0.5)for HP-UX ItaniumE10002-03May 2010These Release Notes describe issues you may encounter with Oracle Database Vault10g Release 2 (10.2.0.5). The Oracle Database Vault installation is covered in detail inthe Oracle Database Vault Installation Guide.This document may be updated after it is released. To check for updates to thisdocument and to view other Oracle documentation, see the Documentation section onthe Oracle Technology Network (OTN) Web site:/technology/documentation/This document contains the following sections:■Installation Issues and Recommendations■Usage Issues and Recommendations■Frequently Asked Questions on Installation■Miscellaneous Notes■Documentation AccessibilityInstallation Issues and RecommendationsThis section describes the known issues pertaining to installation. It also provides theworkarounds that you can use.Cannot Install Oracle Database Vault in a Data Guard EnvironmentBug 5577503The Database Vault installer fails to install Database Vault in an existing physicalstandby database.You can create a new physical standby database by using the following steps:1.Install Database Vault on the primary database.2.Create a physical standby database using a hot backup of the primary database.This backup should include the Oracle home.3.Set up communications between the primary and the physical standby database.Redo logs communicate changes from the primary database to the standbydatabase.Enterprise Manager Does Not Start AutomaticallyBug 5613521After installing Database Vault on a database, and running the postinstallation steps on the nodes, you get an error when trying to access Enterprise Manager.Also, when you try to check the status of dbconsole using the emctl status dbconsole command, you get a message saying that the EM daemon is not running even though the process is running.The workaround is to manually restart the dbconsole process using the following commands:$ORACLE_HOME/bin/emctl stop dbconsole$ORACLE_HOME/bin/emctl start dbconsoleDatabase Instance and Listener Do Not Start Automatically on the Remote Node After Database Vault InstallationBug 6630191After you install Database Vault, the database instances and listeners on the remote nodes do not start automatically. You must start these manually.This is expected behavior. The DVCA utility configures the local node, and starts the database instance and listener processes on the local node. You need to start these processes manually on each of the remote nodes.Cloned Database Vault Home Contains Invalid ObjectsBug 6658315The following steps are used to create a cloned Database Vault instance:1.Install Oracle Database Vault 10g Release 2 (10.2.0.5) in the first Oracle home.2.Clone the first instance to create a second Oracle home.3.Run Net Configuration Assistant (NetCA) and Database Configuration Assistant (DBCA) to configure a listener and database for the cloned instance.4.Run DBCA again to configure Oracle Label Security (OLS) for the cloned instance.5.Run Database Vault Configuration Assistant (DVCA) as follows:$ORACLE_HOME/bin/dvca -action option -oh oracle_home-jdbc_str jdbc_connection_string -sys_passwd SYS_password -owner_accountDV_owner_account_name -owner_passwd DV_owner_account_password-acctmgr_account DV_account_manager_account_name -acctmgr_passwdSee Also:■Article ID 754065.1, titled "Installing Database Vault in a Data Guard Environment" on My Oracle Support (formerlyOracle MetaLink ):https://■Data Guard Concepts and Administration Guide for more information on creating a physical standby databaseDV_account_manager_password -logfile ./dvca.log -nodecryptThe following SQL statement shows that the cloned Database Vault instance contains invalid objects:SQL> select count(*) from all_objects where status = 'INVALID';COUNT(*)----------45The workaround is to run the utlrp.sql script. This script recompiles all PL/SQL modules that might be in an invalid state, including packages, procedures, and types. Use the following commands to run the utlrp.sql script:cd $ORACLE_HOME/rdbms/adminsqlplus SYS "AS SYSDBA"Enter password:SQL> @utlrp.sqlError Occurs When Oracle Database Vault Security Is Configured on a Remote NodeBug 6140164After you add a second node to a single-node Oracle Real Application Clusters (Oracle RAC) installation, the following error occurs when you try to configure Database Vault security for the second node:ORA-32001: write SPFILE requested but no SPFILE specified at startupThe following steps reproduce the bug:1.Install Oracle Cluster Ready Services (CRS) on a 2-node cluster.2.Install Oracle Database Vault on the first node.3.Run the addnode.sh script on the first node to add the second node.4.Configure the database listener and database instance for the second node.5.Run the following ALTER SYSTEM statements on the second node:ALTER SYSTEM SET AUDIT_SYS_OPERATIONS=TRUE SCOPE=SPFILE;ALTER SYSTEM SET OS_ROLES=FALSE SCOPE=SPFILE;ALTER SYSTEM SET RECYCLEBIN='OFF' SCOPE=SPFILE;ALTER SYSTEM SET REMOTE_LOGIN_PASSWORDFILE='EXCLUSIVE' SCOPE=SPFILE;ALTER SYSTEM SET SQL92_SECURITY=TRUE SCOPE=SPFILE;ALTER SYSTEM SET OS_AUTHENT_PREFIX='' SCOPE=SPFILE;The workaround is to run the following steps before running the addnode.sh script in Step 3:Note:These steps must be run from the first node.1.Shut down the database.$ORACLE_HOME/bin/srvctl stop database -d db_name2.Start the database with the nomount option.$ORACLE_HOME/bin/srvctl start database -d db_name -o nomount3.Connect to the database AS SYSDBA.sqlplus SYS "AS SYSDBA"Enter password:4.Create a server parameter file (SPFILE) using the traditional initializationparameter file (PFILE). The initialization parameter file is usually located at$ORACLE_HOME/admin/db_name/pfile for Optimal Flexible Architecture compliant databases.For example:SQL> CREATE SPFILE='SHARED_LOCATION/spfile ORACLE_SID.ora'FROM 'PFILE=ORACLE_HOME/admin/db_name/pfile/init ORACLE_SID.ora'This statement reads the text initialization parameter file to create a server parameter file. You must have the or SYSOPER system privilege to run the CREATE SPFILE statement.5.Shut down the database.$ORACLE_HOME/bin/srvctl stop database -d db_name6.Clear the current contents of the initialization parameter file. Add the serverparameter file location in the initialization parameter file:SPFILE = 'SHARED_LOCATION/spfile ORACLE_SID.ora'7.Restart the database.For example:$ORACLE_HOME/bin/srvctl start database -d db_nameSwap Space Requirement Prerequisite Test FailsBug 7506215The Database Vault installer swap space requirement test may fail in some cases even when enough swap space is available.The swap space required for installation should not exceed 16GB. In case the required swap space is shown as more than 16 GB, this warning can be safely ignored. Prerequisite Check for Kernel Parameters Fails on HP-UX Itanium 11.31 Bug 9591034Prerequisite checks for kernel parameters may fail during Database Vault installation on HP-UX Itanium 11.31.The workaround is to safely ignore the warning message and proceed with the installation.Usage Issues and RecommendationsThis section discusses usage issues that you may encounter with Database Vault. It also provides the workarounds for these issues.Accounts with DV_OWNER, DV_ADMIN, or DV_SECANALYST Role Cannot Use the ALTER USER CommandBug 5161953Accounts with the DV_OWNER, DV_ADMIN, or DV_SECANALYST role cannot run the following command:ALTER USER user QUOTA UNLIMITED ON tablespaceThe workaround is to REVOKE the role from the account, run the ALTER USER command, and then GRANT back the role to the account. This works if the account is not the DV_OWNER account that was created during installation. If the account is the DV_OWNER account created during installation, then you would need to use the following steps:1.Disable the Database Vault command rule for the ALTER USER command.2.Run the ALTER USER command.3.Re-enable the Database Vault command rule for the ALTER USER command.CREATE SESSION Privilege Is Controlled by the Data Dictionary RealmUse the following steps to grant the CREATE SESSION privilege:1.Temporarily disable the data dictionary realm.2.Log in as the SYSTEM user.3.Grant the CREATE SESSION privilege.4.Enable the data dictionary realm.Frequently Asked Questions on InstallationThis section covers some of the frequently asked questions related to Database Vault installation. Oracle Database Vault installation is covered in detail in the Oracle Database Vault Installation Guide .The installer does not detect my existing Oracle Database Enterprise Edition 10g Release 2 (10.2.0.5) instance. What should I do?To allow the installer to find the database instance information, you should check the following:■The database home has Oracle Enterprise Manager Console DB 10.2.0.5.0 installed.■For an Oracle Real Application Clusters (Oracle RAC) database, make sure that Cluster Ready Services (CRS) is running on all nodes.■For an Oracle Real Application Clusters (Oracle RAC) database, make sure that the srvctl utility can be run from the Cluster Ready Services (CRS) home and the Oracle RAC database home.■The file inventory.xml under oraInventory/ContentsXML correctly lists the Oracle home information including the node names (for Oracle RAC).■/var/opt/oracle/oratab has an entry for the database. This entry is case-sensitive.■All database names listed in /var/opt/oracle/oratab have unique system identifier (SID) names.■The file, /var/opt/oracle/oraInst.loc exists.■The oraInventory location is set in the /var/opt/oracle/oraInst.loc file.■The oraInventory location set in /var/opt/oracle/oraInst.loc is the same as the 10.2.0.5 Enterprise Edition database's oraInventory location.■The 10.2.0.5 database home does not have Oracle Database Vault in it.■The 10.2.0.5 database home does not contain an Automatic Storage Management (ASM) instance.I have installed Oracle Database Vault into an Oracle home that has multiple databases. How do I secure the other databases in the Oracle home?You would need to run Database Vault Configuration Assistant (DVCA) manually on the other databases. Refer to the Oracle Database Vault Installation Guide for detailed instructions.I have installed Oracle Database Vault on a Real Application Clusters (Oracle RAC) database instance. How do I secure the other nodes in the cluster?You need to configure Database Vault security on the other Oracle RAC nodes. Refer to the Oracle Database Vault Installation Guide for detailed instructions.Miscellaneous NotesThis section contains miscellaneous notes not covered in the Oracle Database Vault documentation.Snapshots and Materialized ViewsThe keyword SNAPSHOT is supported in place of MATERIALIZED VIEW for backward compatibility.JOB_QUEUE_PROCESSES Initialization ParameterThe JOB_QUEUE_PROCESSES initialization parameter specifies the maximum number of processes that can be created for the execution of jobs. It specifies the number of job queue processes per instance.This parameter must have a non-zero value. The default value for JOB_QUEUE_ PROCESSES is 10.Documentation AccessibilityOur goal is to make Oracle products, services, and supporting documentation accessible to all users, including users that are disabled. To that end, our documentation includes features that make information available to users of assistive technology. This documentation is available in HTML format, and contains markup to facilitate access by the disabled community. Accessibility standards will continue to evolve over time, and Oracle is actively engaged with other market-leading technology vendors to address technical obstacles so that our documentation can be accessible to all of our customers. For more information, visit the Oracle Accessibility Program Web site at /accessibility/.Accessibility of Code Examples in DocumentationScreen readers may not always correctly read the code examples in this document. The conventions for writing code require that closing braces should appear on an otherwise empty line; however, some screen readers may not always read a line of text that consists solely of a bracket or brace.Accessibility of Links to External Web Sites in DocumentationThis documentation may contain links to Web sites of other companies or organizations that Oracle does not own or control. Oracle neither evaluates nor makes any representations regarding the accessibility of these Web sites.Access to Oracle SupportOracle customers have access to electronic support through My Oracle Support. For information, visit /support/contact.html or visit /accessibility/support.html if you are hearing impaired.Oracle Database Vault Release Notes 10g Release 2 (10.2.0.5) for HP-UX ItaniumE10002-03Copyright © 2006, 2010, Oracle and/or its affiliates. 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关于数据库的英语作文A Database is an organized collection of data, typically structured in a way that facilitates efficient storage, retrieval, and manipulation of information. It is a key component in modern computing systems and plays a crucial role in various applications across different industries.Database management systems (DBMS) are software tools that enable users to interact with databases by providing an interface to define, create, query, update, and manage data effectively. There are various types of databases, such as relational databases, hierarchical databases, network databases, object-oriented databases, and NoSQL databases, each with its own advantages and use cases.Relational databases are among the most widely used types of databases, and they organize data into tables with rows and columns. Each table represents a specific entity or object, and relationships between tables are established using keys. SQL (Structured Query Language) is a standard language used to interact with relational databases, allowing users to retrieve, update, and manage data efficiently.In contrast, NoSQL (Not only SQL) databases provide a flexible data model that can handle unstructured andsemi-structured data. They are designed to scale horizontally and are well-suited for applications that require flexible schema designs, high-performance, and scalability, such as web applications, real-time analytics, and big data processing.Database systems are used in a wide range of applications, including customer relationship management (CRM) systems, enterprise resource planning (ERP) systems, inventory management systems, e-commerce platforms, healthcare systems, and more. They store and manage vast amounts of data efficiently, enabling organizations to make informed decisions, streamline operations, enhance productivity, and improve customer satisfaction.Some of the key benefits of using databases include data integrity, data security, data consistency, data concurrency control, and data recovery. By centralizing data storage and providing mechanisms to enforce data integrity constraints, databases ensure that information is accurate, reliable, and accessible when needed.However, maintaining a database requires careful planning, design, implementation, and maintenance to ensure optimalperformance, scalability, and reliability. Database administrators are responsible for overseeing the database environment, monitoring performance, tuning configurations, optimizing queries, managing backups, implementing security measures, and troubleshooting issues.As data continues to grow in volume, variety, and velocity, the demand for advanced database technologies and practices is also increasing. Organizations are leveraging cloud-based databases, distributed databases, in-memory databases, and other innovative solutions to meet the evolving needs of modern applications and services.In conclusion, databases are essential components of information systems that store, organize, and manage data effectively. They play a critical role in enabling businesses, governments, healthcare providers, research institutions, and other organizations to leverage data for decision-making, analysis, reporting, and automation. By understanding the fundamental concepts, principles, and technologies of databases, individuals can build valuable skills and expertise in the field of data management and contribute to the advancement of the digital economy.。
Database Security Issues for Real-Time Electronic Commerce SystemsSang H.SonDept.of Computer ScienceUniversity of VirginiaCharlottesville,VA22903,USAson@AbstractData management and transaction processing are essential in supporting advanced time-critical appli-cations.In many of these applications,security is another important requirement.Security is espe-cially critical in electronic commerce applications where databases often maintain and provide sensi-tive information.In electronic commerce,service providers are sensitive to the needs of the clients, including the implicit(or explicit)timing con-straints.If providing full security to each activity causes the system to become less timely,the service providers would be reluctant in providing necessary security guarantees.Therefore,it is important to consider multiple security service levels for applica-tions such as electronic commerce.In this paper we address issues that the system designers should con-sider for supporting both requirements of timeliness and security.We discuss the issues for transaction and data modeling,and present the notion of partial security.We also discuss a specification language that allows the designer to specify important proper-ties of the database at an appropriate level to sup-port partial security.1.IntroductionA real-time system is one whose basic specification and design correctness arguments must include its ability to meet its timing constraints. This implies that its correctness depends not only on the logical correctness,but also on the timeliness of its actions[Shin94].To function correctly,it must produce a correct result within a specified time, called deadline.In these systems,an action per-formed too late(or even too early)may be useless orThis work was supported in part by National Security Agency grant MDA904-96-1-0096,and by Office of Naval Research.even harmful,even if it is functionally correct. Although it is commonly believed that meeting the timing requirements is a matter of increasing system throughput sufficiently,research in real-time sys-tems has discredited this notion.As real-time systems continue to evolve,their applications become more complex,and often require timely access to(and predictable processing of)massive amounts of data.This need for advanced data management functionalities in real-time systems poses intellectual and engineering challenges that must be tackled to allow for practical solutions to the problems faced in development of real-time database systems.The importance of real-time database systems in an increasing number of applications,such as aerospace and defense sys-tems,industrial automation,business information systems,traffic control,and telecommunication has resulted in an increased research effort in this area [RTDB96,RTDB97].In many of these applica-tions,security is another important requirement, since the system maintains sensitive information to be shared by multiple users with different levels of security clearance.As more and more of such sys-tems are in use,one cannot avoid the need for integrating them.That is,real-time systems have to be made acceptably secure and the secure systems need to support the timeliness requirements of real-time applications.Recently,electronic commerce becomes an interesting application where both security and real-time requirements should be considered together.Electronic commerce is a general concept covering any form of business transaction or infor-mation exchange between organizations of various types,or between service providers and clients, using information and communications technology provided over the Internet.A database is a critical infrastructure that is essential in electronic com-merce to support complex andflexible services tomanage requests in the context of highly dynamic workload with diverged requirements[Ghosh98]. Security is critical in electronic commerce applica-tions where the system often manages sensitive information(such as credit card numbers and account passwords).Building blocks of such an application should ensure security and timeliness to provide mechanisms for searching,negotiating,ord-ering,billing,payment,distribution,contracting, and other client-specific services.In electronic commerce,service providers are usually very sensitive to the needs of the clients, including the implicit(or explicit)timing con-straints.If providing full security to each activity causes the system to become less timely,service providers would be reluctant in providing necessary security guarantees.If the amount of money at stake is below certain threshold(e.g.,less than$10),the system should use mechanisms with less overhead for timely service,although it may involve certain level of risk(e.g.,loss of$10due to incomplete credit check).Traditionally,the notion of security has been considered binary[Ting95].A system is either secure or not.A security hole either exists or not. The problem with such binary notion of security is that in many cases,it is necessary to develop a sys-tem that provides an acceptable level of security and risks,based on the notion of partial security rather than unconditional absolute security,to satisfy other conflicting requirements such as real-time perfor-mance.In that regard,it is important to consider multiple security service levels for applications such as electronic commerce.To achieve that,we need to define the meaning of partial security,for security violations of sensitive data must be strictly con-trolled,while the cost of providing that level of ser-vice should not reduce the timeliness of the system.To improve the timeliness in secure and time-critical applications such as electronic commerce, several issues need to be carefully considered.The research in this area has been focused on identifying architectural and transaction processing issues [Geo97,Muk97,Park97,Son93,Son95,Son97, Son98].It was suggested that a more rigorous model to capture the characteristics and semantics of transactions and data is necessary.This will enable efficient processing to improve the timeliness of the system.In addition,new approaches to supporting both requirements in transaction scheduling and concurrency control that can make trade-offs if necessary,need to be developed and analyzed.Security is concerned with the ability of a sys-tem to enforce a certain policy governing the use, modification,and destruction of information.There are two different policies that have been studied: discretionary security policy and mandatory(or multilevel)security policy.Discretionary security policies define access restrictions based on the iden-tity of users,the type of access,and objects being accessed.While discretionary access control has been used in several systems,it may not be adequate for preventing unauthorized disclosure of the infor-mation[Woo83].The most well-known model for multilevel security is the Bell-LaPadula model [Bell76].In the Bell-LaPadula model,security poli-cies are stated in terms of subjects and objects.A subject is an active entity that can access objects. Every object is assigned a classification,and every subject a clearance.Classifications and clearances are collectively referred to as security classes(or levels)and they are partially ordered.The Bell-LaPadula model imposes the following restrictions on all data accesses:(1)Simple Security Property:A subject is allowedread access to an object only if the former’sclearance is identical to or higher(in the par-tial order)than the latter’s classification. (2)The*-Property:A subject is allowed writeaccess to an object only if the former’s clear-ance is identical to or lower than the latter’sclassification.Database systems that support the Bell-LaPadula properties are called multilevel secure database systems.The Bell-LaPadula model prevents directflow of information from a higher access class to a lower access class,but the condi-tions are not sufficient to ensure that security is not violated indirectly through what is known as covert channels[Lamp73].A covert channel allows indirect transfer of information from a subject at a higher access class to a subject at a lower access class.An important class of covert channels that are usually associated with concurrency control mechanisms are timing channels.A timing channel arises when a resource or object in the database is shared between subjects with different access classes.One way to eliminate covert channels is todesign a system that meets the requirements of non-interference[Gog84].From our earlier study,it became clear that security requirements are not compatible with real-time requirements[Son93,Son95].Frequently, priority inversion is necessary to avoid covert chan-nels.Consider a transaction with a high security level and a high priority entering the database,and it finds that a transaction with a lower security level and a lower priority holds a write lock on a data item that it needs to access.If the system preempts the lower priority transaction to allow the higher priority transaction to execute,the principle of non-interference is violated,for the presence of a high security transaction affects the execution of a lower security transaction.On the other hand,if the system delays the high priority transaction,a priority inver-sion occurs.The system has encountered an unresolvable conflict.In general,these unresolvable conflicts occur when two transactions contend for the same resource,with one transaction having both a higher security level and a higher priority level than the other.Therefore,creating a database that is com-pletely secure and strictly meets real-time require-ments is not feasible.A system that wishes to accomplish the fusion of multi-level security and real-time requirements must make some concessions at times.An important but challenging problem to be addressed in supporting security and real-time is identifying the correct metrics to evaluate the level of security obtained in an adaptable system.In this paper,we discuss issues for transaction and data modeling,and present the notion of partial security.We also discuss requirement specification that allows the designer to specify important proper-ties of the database at an appropriate level to support that notion.Major concerns are the impact on sys-tem timeliness associated with the introduction of security requirements.The rest of the paper is organized as the fol-lowing.In the next section,we present an approach to developing a model for secure real-time data objects and transactions.Section3discusses the notion of partial security and Section4presents a specification language to specify requirements and the rules to resolve conflicts at run-time.Section5 concludes the paper with the planned future work.2.A Model for Data and TransactionsTransaction processing in database systems for electronic commerce may require different data models and correctness criteria to support security and timeliness.Most real-time database scheduling algorithms have been developed and evaluated under almost the same workload and operating environment model as used in conventional database systems.While this model is suited to some real-time database applications,in electronic commerce where real-time and security requirements need to be satisfied,different characteristics and semantics of their data and transactions should be utilized.Databases used in electronic commerce store transactions and data that might need to be updated when transaction occur.Several different types of transactions may need to be executed on the data-bases.For example,in stock trading application,the database should keep track of several hundreds of thousands offinancial instruments world-wide.The stream of update requests can be up to500 updates/second during peek time[Coch94].Many of them could be periodic while some others could be triggered to compute indices or other composite values on request.At the same time,clients of the system may submit transactions to check the price and perform trading on specific stocks.Some of the timing constraints associated with them could be critical,while others can be soft.Some of the data may be accessible to all the clients,while access to certain sensitive information is restricted only to privileged members.To achieve such restrictions, different portions of the database may have different access control policies based on the user status. Various security-assurance techniques can be used, ranging from user authentication using encrypted passwords for the database to encrypted storage of highly sensitive data in the database.We have developed a model for data and tran-sactions for both soft and critical real-time systems [Kim96].The model provides a strong basis not only for performance study of real-time transactions but also characteristics and requirements of real-time database systems to support different classes of transactions.In that model,a real-time database consists of a set of data objects representing the state of an external world.There are two types of data objects in a real-time database system:continuous and discrete.Continuous data objects are related with exter-nal objects continuously changing with time.The value of a continuous data object can be obtained directly from external world(image object)or com-puted from the values of a set of image data objects (derived object)with a regular interval.Discrete data objects are static in the sense that their values do not depend on the value of any continuous data object.In other words,the values of discrete data objects do not become obsolete as time passes,but are valid until update transactions actually change the values.Based on the nature of transactions in real-time database systems,they can be characterized by the following attributes:implication of missing specified timing constraints,arrival pattern,data access pattern,data requirement,resource require-ment,and data types to be accessed.Considering those characteristics of real-time data and transac-tions,there are hundreds of possible transaction classes.However,some of them are infeasible and others can be grouped together to be processed dif-ferently.Most real-time database researchers use a model that includes only a subset of the above classes and never discriminate transactions in the system.However,in practice,all kinds of transac-tions can coexist in one system.The performance goal of such a real-time database system isfirst to guarantee all critical timing constraints of transac-tions,to achieve the performance requirements of transactions given by the form of timeliness,and finally to minimize the deadline miss ratio(or max-imize the total values)of soft real-time transactions. To achieve this performance goal,it is necessary to apply different transaction scheduling and con-currency control algorithms to each type of transac-tions.An important question to ask is what are the implications of introducing security requirements into the model.Three categories of data(image, derived,and discrete)should be further classified according to their security levels.This will lead to more complex methods in satisfying the consistency and timeliness requirements,while meeting the security requirements.In fact,the database may not be able to satisfy all three requirements during cer-tain intervals of time,when different processing schemes are used for each type of transactions.It is because that a certain type of transactions need to be executed separately from transactions of other types to satisfy timeliness,even though the security and consistency requirements indicate that there is a cer-tain relationship among those transactions to be maintained.In our model,a typical real-time data-base application consists of the following classes of transactions:Class I Transactions:This class includes periodic transactions with critical deadlines.All the data and run-time requirements are supposed to be available for Class I transactions in advance.Since Class I transactions write only into continuous data objects that require only temporal consistency,it is feasible to guarantee their critical timing constraints under an appropriate scheduling algorithm.Class II Transactions:Transactions of this class have critical timing constraints which come from their response-time requirements,unlike the timing constraints of Class I transactions which come from the attributes of data.However,they are not neces-sarily periodic and a priori knowledge of their resource requirements is not completely available. Also,they may access discrete data objects which require serializable accesses.For this reason,we cannot always guarantee that a Class II transaction will meet its deadline.This is the transaction class in which each transaction can have a different guarantee level as its performance requirement. Class III Transactions:All real-time transactions not belonging to any of the above classes are categorized in this group.They have either soft or firm deadlines,their data and run-time requirements are not always known,and they can access both con-tinuous and discrete data objects.Class III transac-tions can be further divided into several classes and processed differently.For example,a priori knowledge of the attributes of a transaction is some-times available for some soft real-time transactions and should be utilized to improve the system perfor-mance.Much work has been already done for Class III transactions[Abbo92,Lam97,Lee96].To support security and timeliness require-ments in database systems for electronic commerce, it will be useful to classify different types of transac-tions based on their security requirements,and develop processing schemes for each type of tran-sactions.A model should include security features as outlined in the following:(1)Different from data objects in traditional data-bases,continuous data objects that representthe state of the external world should haveadditional attributes such as timestamp(thetime at which the value was introduced),tem-poral validity duration(during which the valueis believed to be valid),and security level.Acontinuous secure data object is in a correctstate if and only if the value of the objectsatisfies the temporal validity requirement andit is maintained according to the non-interference rule.Both continuous anddiscrete secure objects must be accessed fol-lowing the access control policies specified. (2)A transaction should have the additional attri-butes such as arrival time,deadline,periodi-city,criticality,execution time estimate,resource requirements,and security level.According to the values of these attributes,transactions can be categorized into hierarchyof classes.Transactions can be grouped according to the classification scheme as discussed above:Class I:Critical and periodic transactions.Class II:Critical and aperiodic transactions.Class III:Non-critical transactions.Each class can be further categorized according to their security levels.For example,there will be Class I.1(top secret Class I),Class I.2(secret Class I),Class I.3(confidential Class I),and so -patibility among different accesses to secure data objects by transactions from different classes need to be carefully designed to be used for specifying the correctness of multilevel secure transaction pro-cessing.If a database utilizes the characteristics of data and transactions as discussed above,it can make decisions to further improve the system per-formance in meeting the security and timeliness requirements.It can also consider necessary trade-offs to be made in case both requirements cannot be met at the same time.3.Partial SecurityTo achieve the desired level of timeliness,the system may need to allow potential security viola-tions at times.When the system has to trade-off security,the system is no longer completely secure; rather it only will be partially secure.In that case,it is extremely important to define the exact meaning of partial security.In fact,several security practi-tioners recognize that complete security is a fallacy ---there is no system completely secure.In one way or the other,any operational system becomes vulnerable to security leaks.The real question is how we can make the system acceptably secure while it remains available and provides timely ser-vices.With appropriate policies and the mechan-isms to enforce them in the system,we provide the increased availability and timeliness in situations where other systems without such capability may just freeze or stop operating to ensure the(ima-ginary)complete security.Two of the major research issues to be addressed are1)to identify pol-icies to specify quantitative levels of partial security, and2)mechanisms to enforce the required level of partial security.One approach could be to define security in terms of a percentage of potential security violations allowed in the system.However,this approach is not useful because it is a bad metric.Even though a system may allow a very low percentage of security violations,this fact alone reveals nothing about the security of individual data.For example,a system might achieve99%security level,but that1%of insecurity might allow the most sensitive piece of data to leak out.For serious security applications,a more precise metric is necessary.A better approach involves adapting the Bell-LaPadula security model and defining security requirements such that partial security could be allowed only between certain security levels.In this way,the designer can specify that the most sensitive information will never be allowed to be involved in potential security violations.Initially,the system may support the original Bell-LaPadula security model.As the real-time performance of the system degrades,the system allows more potential security violations and reduces the number of security confling this scheme,we can still make guarantees about the security of the data,based on the specification of the security policy.For example,consider a system with four security levels:top secret,secret,confidential,and unclassified.Partial security policies can be specified by the level of security guarantees pro-vided,from fully secure to completely insecure.Forinstance,level-4security indicates full security, regardless of the real-time performance of the sys-tem.As guarantee levels are lowered,potential security violations are allowed between certain lev-els.For a level-3security guarantee,transactions that are at the unclassified level may have conflicts with transactions at the confidential level in access-ing unclassified data,resulting in a potential covert channel.In a sense,this represents a system with only three security levels:top secret,secret,and unclassified.However,it does not mean that there is no distinction between confidential and unclassified levels.Transactions that are at the unclassified level cannot directly access confidential data.It is possible to combine this approach with other methods of specifying the degree of potential security violations.For example,we can use the bandwidth of the covert channels that may show up as the result of the security violation,or use the fre-quency of such violations in terms of the percen-tages to define partial security.In this way,the amount of security violations between two levels for which partial security is allowed would be required to fall below the specified bandwidth or frequency. Note that guarantees can still be made between lev-els designated as allowing no security violations;for the other levels,database designers can use different bandwidth/frequency to denote their preferences on where and how much they would rather have the potential security violations occur.To be useful in real applications,different par-tial security policies need to be identified so that the policy makers can decide which one is acceptable, considering potential violations and their conse-quences.In many cases,it would be helpful if par-tial security policies are in a strict partial order in terms of satisfying the timeliness and security requirements.Detection of potential security violations is a key requirement to support any partial security poli-cies.Whenever two activities(e.g.,transactions)at different security levels share a resource,there is a potential for security violation.At the data object level,such detection can be done by the transaction scheduler and data manager.It is possible that there are other potential security violations in the system that cannot be systematically detected.However, without proper detection mechanisms,there is noth-ing much we can do about it.The security policies discussed in this paper deals with potential violations that can be detected.4.Specification of RequirementsApplication designers should be able to specify semantic information using a specification language to express the relative importance of keep-ing the desired level of security and meeting the timeliness requirement.A question to be addressed in that approach is the verification of the given specification.Specifications should be compiled and verified to check any inconsistency in the require-ments and to clearly determine the necessary actions to be taken.In this section,we present a simple specification language that could be used to allow the designer to specify the database semantics and real-time/security requirements.The language should be able to support the designer in specifying rules which could be referred at run-time to resolve the conflicts.Once the specification is given,it needs to be analyzed to identify any inconsistency and to gen-erate rules based on the semantic information on data and transactions to be used at run-time.One approach to specifying the security and real-time requirements is a tool that aids the designerfirst with locating conflicts and then with denoting their preferences according to the semantics of the data-base.4.1.Specification LanguageThe specification language should allow designers to create rules at varying levels of detail. In applications where much information is known about the database beforehand,designers can control security and real-time aspects of the database much more tightly than in situations where less is known beforehand or such a tight control is not required. There should be multiple levels of detail in the specification scheme.If appropriate,the designer should be able to use all the levels to specify the requirements.There are three levels of detail in our specification scheme.In the specification language we are develop-ing,the specification consists of two parts:a description of the database and a set of rules to fol-low when conflicts arise.The description provides a framework for the rules.The specification of both the description and the rules varies between the dif-ferent levels of details.Regardless of the levels ofdetails that are used,thefirst part of the specification contains facts about the database as a whole.Here, the designer specifies the number of data items,the number of security levels,and the number of prior-ity levels used in the entire database.It also allows to specify any detail information regarding transac-tions that can be invoked.Information about transactions and data should be specified.Transactions are given a number of components.Each transaction is given a readset and a writeset.These can consist of any number of data items.If no readset or writeset is given,they are assumed to be empty.The real-time requirements of a transaction are given by four variables:priority, execution time,release time,and periodicity.The periodicity of a transaction defines how often it starts executing,and the release time indicates the offset of the periodic start.Finally,transactions are given a security level.Data items are specified by number,and each data item is given a security level.The specification can also contain a default security level,which is assigned to any unspecified data items.All of the information about transactions and data belong to the description portion of the specification.Not all of these components for transactions and data are required.In general purpose database systems,some of the information might be hard to specify.How-ever,in many real-time applications,most informa-tion is available,since such information is necessary for schedulability analysis of the system to support the timeliness and predictability requirements.In fact,in real-time database systems,many transac-tions are periodic and their access pattern is known. The only truly necessary components are the secu-rity level and the priority level.If a designer leaves out,for example,the readset or the writeset,the specification processing tool cannot make any assumptions about the data accessed by this transac-tion,so it must assume that the transaction may conflict with every other transaction.The second part of the specification presents a set of rules at varying levels of detail.The rules define the system behavior when conflicts occur. These rules can either be static or dynamic.Static rules apply to conflicts that are resolved in the same way every time.For example,the user might specify that a conflict between two specific transactions,or two categories of transactions,will never result in a security violation.Dynamic rules can depend on certain run-time variables that the database keeps track of during execution.In our scheme,dynamic rules can be based on three different system vari-ables:security violation percentage,transaction miss percentage(the percentage of transactions that have missed their deadlines),and the number of consecu-tive missed deadlines.Each dynamic rule has a list of clauses and a default action.A clause contains a Boolean comparator(>,>=,=,<,or<=)between these three system variables and a constant value. Each clause contains an action to be taken if the Boolean comparison is true.When a conflict is encountered by the database system,it checks thefirst clause.If that clause is true,it takes the associated action.If not,it checks the next clause,and so on.Therefore,the designer should be careful in determining the evaluation order of the rules.If none of the clauses turns out to be true,the database takes the default action.For example,a rule might be"If the security violation percentage is greater than5,violate security.Other-wise violate timeliness."Here,the"otherwise"sen-tence represents the default action.In thefirst,most detailed level,the designer can generate rules for specific transactions.The second level of specification detail replaces specific transactions with categories of transactions.Tran-sactions are categorized by their security levels and priority levels.The designer can create any number of categories at any granularity that he or she feels is appropriate,and describes these categorizations in the description portion of the specification.Then, rules are created for conflicts between categories of transactions.These rules are the same as the rules for thefirst level.In the third level of specification,designers create a set of rules describing actions to be taken in case of conflicts that are not specified in the lower levels.This can be considered as the general system policy.Conditions would depend on the charac-teristics of the transactions that are conflicting or the current performance statistics.Depending on the results of the comparison,the rule would mandate either a security violation or a priority violation.All of this information belongs in the rules portion of the specification;nothing is needed in the descrip-tion portion.By carefully creating the rules,the database designer can implement the partial security policy suitable for the application.。
