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计算机过去和现在的变化英语作文Computers: Then and NowComputers are amazing machines that have changed so much over the years! When I think about how computers used to be a long time ago, it's hard to believe we used those big, clunky things. Nowadays, computers are sleek, portable, and can do incredible things. Let me tell you all about the wild changes computers have gone through.Way back in the old days, computers were these huge boxes that took up entire rooms! They were called "mainframe computers" and they looked like weird metal cabinets with lots of blinking lights and dials. Just one of those ancient computers was heavier than a baby elephant! Can you imagine having to lug one of those around? No way!The mainframe computers didn't even have a screen to look at. All the inputs had to be done with punched cards or reels of tape. It must have been so annoying to program those computers by just poking holes in stacks of cards. If you made one little mistake, you had to start all over! Yikes!These dinosaur computers could only do very basic calculations and tasks. It would take hours or even days for themto solve a single math problem that our phones can do in a split second today. The earliest computers were basically just glorified calculators. Crazy, right?As computers advanced over the decades, they started getting a bit smaller and more powerful. Instead of taking up an entire room, they shrank down to being the size of a refrigerator. These were called "minicomputers" which is a funny name since they were still pretty huge!Eventually computers evolved into these boxy "desktop" shapes that could sit on an office desk. The first desktop computer that many people got for their homes was called the IBM PC which came out in 1981. It had a small screen and you could play basic games and type documents on it. Those dinosaur desktops look so ancient compared to the sleekflat-screen models we have now!One of the coolest developments in computer history was the creation of the laptop computer. These portable computers allowed people to take their work or gaming anywhere they went. The very first laptop released in 1981 was called the Osborne 1 and it weighed a whopping 24 pounds! I can't imagine lugging around a laptop computer that weighs as much as a toddler. How did people's arms not break back then?Over time, laptops got much thinner, lighter, and far more powerful. Nowadays we have these incredible ultrabooks and tablets that are lighter than a textbook but can run massive video games, edit movies, and let us video chat with anyone around the world. It's amazing that so much computing power can fit in such a tiny portable device.Speaking of portable, the greatest computer breakthrough in recent history has definitely been the invention of the smartphone. These little pocket computers put a device far more powerful than those old dinosaur desktops right in the palm of our hands! With a smartphone, you can browse the entire internet, stream endless videos and music, play immersive 3D games, and even use augmented reality to see computerized images blended with the real world around you. Smartphones transcend what we used to think of as a "computer" and have become brilliant all-in-one devices vital to our modern lives.Not only have the computers themselves transformed dramatically, but the ways we interact with them have evolved as well. Those ancient mainframe computers had to be programmed in frustratingly cryptic languages of numbers and symbols. Then we progressed to using keyboard commands tocontrol computers, which was way easier even if we had to memorize tons of shortcut key combinations.Nowadays we can control our computers and phones so intuitively with touchscreens, voice commands, hand gestures, and even having our eye movements tracked. Heck, we can now just think about what we want a computer to do and it will happen with the help of mind-reading headsets! I still can't believe something that used to require feeding stacks of punched cards into a multi-ton metal cabinet can now be achieved by just looking or nodding at a sleek little device that fits in my pocket. Mind-blowing!The way computers look and function has been revolutionized beyond anything the pioneer programmers and engineers of the past could have dreamed. And you know what the wildest part is? Experts say the computer revolution is just getting started. They predict that in our lifetimes we could see hyper-realistic 3D hologram computers,.molecular computers built from individual atoms, and maybe even powerful quantum computers that operate on mind-bending physics.Just imagining what computers might look like in 30 or 40 years makes my head spin. Will we have shape-shifting computers that can morph from something handheld to a laptopto a room-sized display? Will we be able to send data and programs across galaxies instantly without any wires or networks? Will we link our brains directly to computer clouds filled with unimaginable knowledge and processing power? Whatever happens, I know computers are going to keep evolving in ways that make today's marvels seem like prehistoric fossils.In my opinion, the journey computers have gone through so far has been one of the most amazing technological adventures in human history. Thinking about how we went from hulking mechanical brains bigger than mammoths to having versatile pocket supercomputers is just flat-out mind-boggling. I can't wait to see what crazy new computer frontiers are cracked in the decades to come! One thing's for sure - the best is yet to come for these incredible thinking machines we call computers.。
电脑英文作文简短英文：As a computer, I am an indispensable part of people's daily life. From work to entertainment, people rely on meto complete various tasks. I can help people to write documents, create presentations, browse the Internet, play games, and so on. With the development of technology, I am becoming more and more intelligent, and my functions are constantly updated and improved.However, as a machine, I do have some limitations. For example, I cannot feel emotions or understand human feelings. Sometimes people may get frustrated when I failto complete a task or encounter a technical problem. But I am always here to help, and people can always findsolutions to these problems.In conclusion, I am just a tool, but a very useful tool. People can use me to achieve their goals and make theirlives easier and more convenient. As long as people treat me well and take good care of me, I will always be their loyal assistant.中文：作为一台电脑，我是人们日常生活中不可或缺的一部分。
电脑系统各种英文文件夹的意思（国外英语资料）一、系统文件夹释义1. "Documents"（文档）：这个文件夹通常用于存储用户创建的文档、电子表格、演示文稿等文件。
2. "Downloads"（）：当您从互联网上文件时，默认情况下，这些文件会被保存在这个文件夹里。
3. "Music"（音乐）：这个文件夹用于存放音乐文件，包括MP3、WAV、FLAC等格式。
4. "Pictures"（图片）：在这里，您可以找到您的照片、截图和其他图像文件。
5. "Videos"（视频）：这个文件夹用于存储视频文件，如AVI、MP4、MOV等格式。
6. "Desktop"（桌面）：桌面文件夹包含了您桌面上显示的文件和文件夹快捷方式。
二、系统文件夹路径释义1. "Program Files"（程序文件）：这个文件夹包含了大部分安装在本机上的应用程序。
通常路径为 C:\Program Files 或C:\Program Files (x)。
2. "Program Files (x)"：在64位操作系统上，这个文件夹用于存放32位应用程序。
3. "Windows"：这是操作系统的核心文件夹，包含了系统文件和系统设置。
4. "Users"：这个文件夹包含了所有用户账户的个人信息，如文档、桌面、等。
5. "AppData"：这是一个隐藏文件夹，包含了应用程序的设置和缓存文件。
通常路径为 C:\Users\用户名\AppData。
三、常见英文文件夹缩写释义1. "App"：通常指应用程序（Application）。
2. "Cfg" 或 "Config"：表示配置（Configuration）。
计算机的作文英语Title: The Transformative Power of Computers。
In today's rapidly evolving world, computers have become indispensable tools, permeating every aspect of our lives. From education to entertainment, from business to healthcare, the influence of computers is ubiquitous. In this essay, we will explore the profound impact that computers have had on society, delving into their role in education, communication, innovation, and beyond.Firstly, let us consider the realm of education. Computers have revolutionized the way we learn, making information more accessible and interactive. With the internet at our fingertips, students can explore vast repositories of knowledge, accessing resources that were once confined to the pages of textbooks. Online courses and educational software offer personalized learning experiences, catering to individual needs and preferences. Moreover, computers facilitate collaborative learning,enabling students to connect with peers and experts from around the globe.In addition to education, computers have transformed the way we communicate. Social media platforms, email, and instant messaging have revolutionized interpersonal interactions, transcending geographical barriers and fostering global connections. Through video conferencing and virtual reality, we can engage in face-to-face communication with people thousands of miles away, strengthening relationships and facilitating collaboration. Furthermore, the rise of social networking has given rise to new forms of expression and activism, empowering individuals to voice their opinions and effect change on a global scale.Furthermore, computers have been catalysts for innovation, driving advancements in science, technology, and industry. From the simulation of complex phenomena to the optimization of industrial processes, computers have accelerated the pace of discovery and invention. Artificial intelligence and machine learning algorithms haverevolutionized fields such as healthcare, finance, and transportation, offering new insights and solutions to age-old problems. Moreover, the democratization of technology has empowered entrepreneurs and startups to disrupt traditional industries, fueling economic growth and job creation.Beyond their practical applications, computers have also enriched our lives in countless ways. From entertainment to art, from gaming to digital media, computers have expanded the boundaries of creativity and expression. Through digital art and virtual reality experiences, artists can create immersive worlds that defy conventional limitations, transporting audiences to new realms of imagination. Likewise, interactive gaming experiences offer players unprecedented levels of engagement and immersion, blurring the lines betweenreality and fantasy.In conclusion, computers have fundamentally transformed society, reshaping the way we learn, communicate, innovate, and create. As we continue to harness the power oftechnology, it is essential to ensure that its benefits are accessible to all and that its impact is guided by ethical considerations. By embracing the transformative potential of computers, we can build a more connected, informed, and inclusive world for future generations.。
计算机英语作文Title: The Impact of Computers on Modern Society。
In today's interconnected world, computers play an indispensable role in various aspects of our lives, revolutionizing the way we work, communicate, and interact with the world around us. From enhancing efficiency in industries to facilitating communication across continents, the influence of computers is pervasive. This essay delves into the profound impact of computers on modern society, exploring their significance, benefits, and challenges.First and foremost, computers have significantly transformed the landscape of the workplace. With the advent of computer technology, tasks that once required extensive manual labor and time can now be accomplished with remarkable speed and precision. From automated manufacturing processes to sophisticated data analysis, computers have revolutionized industries, leading to increased productivity and efficiency.Moreover, computers have revolutionized communication, enabling instant and seamless connectivity across the globe. Through email, social media platforms, and video conferencing tools, individuals can communicate and collaborate irrespective of geographical barriers. This interconnectedness has facilitated the exchange of ideas, knowledge, and cultural experiences, fostering global understanding and cooperation.In addition to their impact on work and communication, computers have also revolutionized education. Theintegration of computers into classrooms has transformed traditional teaching methods, making learning more interactive, engaging, and accessible. With access toonline resources and educational software, students cantailor their learning experiences to suit their individual needs and preferences, thereby enhancing academic outcomes.Furthermore, computers have revolutionizedentertainment and leisure activities. From streaming services that provide instant access to a vast array ofmedia content to immersive gaming experiences, computers have redefined how we entertain ourselves. Virtual reality (VR) technology, powered by computers, has opened up new frontiers in entertainment, offering immersive experiences that blur the lines between the physical and digital worlds.Despite the myriad benefits that computers offer, their pervasive presence in society also presents challenges and concerns. One of the primary concerns is the issue ofprivacy and data security. As we increasingly rely on computers to store and process sensitive information, safeguarding data privacy becomes paramount. Instances of data breaches and cyberattacks highlight the need forrobust cybersecurity measures to protect individuals and organizations from digital threats.Moreover, the rapid advancement of computer technology raises concerns about its impact on employment and the workforce. While computers have automated many routine tasks, there is a growing fear that they may lead to job displacement and exacerbate inequality. It is essential to address these concerns through policies that promoteretraining and upskilling initiatives to ensure that individuals are equipped with the necessary skills tothrive in the digital age.In conclusion, computers have profoundly transformed modern society, revolutionizing the way we work, communicate, learn, and entertain ourselves. Their pervasive presence has brought about significant benefits, from increased productivity and efficiency to enhanced connectivity and access to information. However, their widespread adoption also poses challenges, such as ensuring data security and addressing concerns about job displacement. Moving forward, it is crucial to harness the power of computers while mitigating their potential risks, ensuring that technology serves the greater good of humanity.。
计算机英语四级作文Computer English CET-4 Essay。
With the rapid development of computer technology, computers have become an indispensable part of our daily life. As a result, computer English has become increasingly important. In this essay, I will discuss the significance of computer English and its impact on our lives.Firstly, computer English is essential for communication in the field of information technology. As we all know, English is the lingua franca in the world of technology, and computer English is no exception. Without a good command of computer English, it is impossible to communicate effectively with colleagues and clients in this field. Therefore, computer English is a must for anyone who wants to work in the IT industry.Secondly, computer English is important for learning new technologies. Most of the new technologies aredeveloped in English-speaking countries, and the technical documentation and manuals are written in English. Therefore, if we want to learn these new technologies, we need to be proficient in computer English. Moreover, many online courses and tutorials are also in English, which further emphasizes the importance of computer English in learning new technologies.Thirdly, computer English has a significant impact on our daily lives. With the advent of the internet, we are now living in a global village where we can communicatewith people from all over the world. However, to take full advantage of the internet, we need to be proficient in computer English. For example, we need to be able to read and write emails, chat with friends on social media, and search for information on the internet. Without a good command of computer English, we will be at a disadvantagein the digital age.In conclusion, computer English is an essential skill that everyone should possess in the modern world. It is not only important for communication and learning newtechnologies but also has a significant impact on our daily lives. Therefore, we should make an effort to improve our computer English skills through practice and study.。
计算机的作文英语作文Computer has become an indispensable part of our daily life. It has brought about enormous changes in the way we live, work and communicate. In this essay, I will discuss the impact of computer on our society, economy and education.Firstly, computer has revolutionized the way we work. It has made many jobs easier and more efficient. For example, in the past, people had to do all the calculations by hand, but now, with the help of computer, they can do it much faster and more accurately. Moreover, computer has also created many new jobs, such as software engineers, web developers and data analysts.Secondly, computer has greatly influenced our social life. With the development of social media, people can communicate with each other easily and quickly. They can share their thoughts, feelings and experiences with others, no matter where they are. In addition, computer has alsochanged the way we entertain ourselves. We can watch movies, play games and listen to music on our computers, which has brought us a lot of fun and relaxation.Thirdly, computer has had a significant impact on our economy. It has made many businesses more efficient and profitable. For example, online shopping has become very popular, which has greatly boosted the sales of many companies. Moreover, computer has also created many new business opportunities, such as e-commerce and online advertising.Lastly, computer has changed the way we learn and educate ourselves. With the help of computer, we can access a vast amount of information and knowledge on the internet. We can learn new skills, take online courses and even earn degrees from prestigious universities without leaving our homes. This has greatly expanded our opportunities for education and personal growth.In conclusion, computer has become an essential tool in our daily life. It has brought about many benefits andopportunities, but also some challenges and risks. We need to use it wisely and responsibly, and keep exploring its potential to make our world a better place.。
1.1仔细看看处理器和主存储器我们已经知道，所有的计算机都具有相似的能力，并且在本质上执行相同的功能，尽管一些可能会比另一些快一点。
我们也知道，一个计算机系统具有输入，输出，存储和处理部件；处理器是一个计算机系统智能核心，并且一个计算机系统可以有许多个处理器。
我们已经讨论过如何在计算机系统内部，用被称作“位”的电子状态来表现数据，现在我们要弄明白计算机系统的核心，即处理器，的内在的工作方式。
计算机的内部操作很有意思，但确实没有什么神秘可言。
所谓的神秘只是存在于那些听信传闻和相信科幻小说作家的人的意识中。
计算机就是一种没有思想的需要接通电源的电子设备而已，与烤面包机和台灯差不多。
不加夸张地讲，市场上有几百种不同类型的计算机在销售.每种电脑在复杂性上可能有很大区别，但归根结底,每种处理器，有时称为中央处理器即cpu，只有两个基本部分:控制单元和计算逻辑单元.主内存在处理器内部操作中也是一个不可缺少的部分.这三个部件--主内存，控制单元和计算逻辑单元--一起工作.然我们看看它们(各自的)功能和它们之间的联系主存与其他的辅助存储器（如：磁带、硬盘）不一样的是，主存不含有运转部件。
由于没有机械运转的需要，主存种数据访问可以达到电子的速度，或接近于光速。
当今计算机的主存大多数使用DRAM（动态随机存取存储器）技术。
目前最新的工艺水平是：一块只有大约1/8张邮票大小的DRAM芯片却可以存储大约256,000,000位，约25,6000,000个字符的数据。
主存储器，也就是说内存，用于为处理器暂时存放程序和数据。
所有的程序和数据在被操作之前必须从输入设备（如VDT）或者辅助存储器转存到主存储器中。
主存储器存储容量通常是相当有限的，因此，在一个程序执行结束，它所占用的存储空间必须被重新分配给其它正在等待执行操作的程序。
图 1-1描述了输入/输出设备与主存储器间的读和写过程。
在图中，VDT发出一个输入请求，请求是以消息模式通过通道（如同轴电缆）发送到主存储器。
介绍计算机英语作文Title: The Role of Computers in Modern Society。
In today's fast-paced world, computers have become an indispensable part of our daily lives, revolutionizing the way we communicate, work, and live. From the simplest tasks to the most complex operations, computers havesignificantly impacted various aspects of human existence. This essay will delve into the significance of computers in modern society, exploring their multifaceted roles and the implications they have for individuals, businesses, and communities.First and foremost, computers have revolutionized communication. Through the internet and various communication software, people can connect with others globally in real-time, transcending geographical boundaries. Email, social media platforms, and instant messaging services have become integral tools for personal and professional communication, enabling individuals to stayconnected, share information, and collaborate regardless of distance.Furthermore, computers have transformed the way we work. In the business world, computer technology has streamlined processes, increased efficiency, and expanded opportunities for innovation. From automated manufacturing systems to sophisticated data analytics tools, computers have empowered organizations to optimize their operations, make data-driven decisions, and gain a competitive edge in the marketplace. Additionally, remote work has become increasingly prevalent, facilitated by the connectivity and flexibility afforded by computers, allowing employees to work from anywhere with an internet connection.Moreover, computers have revolutionized education. The integration of technology in classrooms has enhancedlearning experiences, making education more interactive, engaging, and accessible. Interactive whiteboards, educational software, and online resources have augmented traditional teaching methods, catering to diverse learning styles and fostering critical thinking skills amongstudents. Furthermore, e-learning platforms and online courses have democratized education, providing individuals with opportunities for self-paced learning and skill development regardless of their geographical location or socioeconomic background.In addition to communication, work, and education, computers have also had a profound impact on entertainment and leisure activities. From streaming services and online gaming to virtual reality experiences, computers have transformed the way we consume media and entertain ourselves. The advent of digital content creation tools has empowered individuals to express their creativity, share their passions, and connect with like-minded communities online. Furthermore, the rise of e-commerce platforms has revolutionized the way we shop, offering unparalleled convenience, choice, and accessibility to consumers worldwide.However, alongside the myriad benefits that computers bring, there are also challenges and concerns that must be addressed. Issues such as cybersecurity threats, dataprivacy breaches, and digital divide disparities underscore the need for responsible use and governance of computer technology. As our reliance on computers continues to grow, it is essential to prioritize cybersecurity measures, enact robust data protection regulations, and bridge the digital divide to ensure that everyone has equitable access to the opportunities afforded by technology.In conclusion, computers play an indispensable role in modern society, impacting various aspects of our lives from communication and work to education and entertainment. As we navigate the ever-evolving landscape of technology, it is crucial to harness the transformative power of computers responsibly, addressing challenges and maximizing benefits to create a more connected, inclusive, and prosperousfuture for all.。
Technology And SQL Server is based on the common language of compiler operation of the procedure, its strength and stability, can make it runs on the Web application of software developers almost all of the platform. The common language of basic library, information mechanism, data interface treatment can seamlessly integrate into the Web applications. is also independent language language - feasibility of, so, you can choose a kind of the most suitable for your language to write your program, or put your program in a number of language to write, now support with c # (c + + and Java combination), VB, Jscript, c + +, F++. In the future, such a variety of program language collaborative working ability to protect your present based on COM + development program, can complete transplant to . generally fall into two kind of development language, using the and c #, c # relatively common, because it is unique language, using the VB programming is used, suitable for VB programmers, if before new , no other development experience with language, suggest direct study c # can. to run some very common tasks such as form submission of client identity authentication, distribution system and website configuration became very simple. For example page framework allows you to build your own user boundary surface, make it different from common VB - Like interface. using a character basis, classification of the allocation system, make your server environment and application Settings more simple. Because configuration information is stored on simple text, new Settings may need not start local administrator tools can be achieved. Known as the "Zero Local under the" philosophy that application development based on the more specific, and quick. An application in a server system installation simply copy some must file, do not need system reboot, everything is so simple. Multiprocessor environment reliability has been deliberately designed as a can be used for multiprocessor development tool, it on a multiprocessor environment with special seamless connection technology, will greatly increase speed. Even if you now my application software is developed for one processor, future multiprocessor runtime don't need any change can improve their efficiency, but now the ASP but cannot do this. Custom sex and expansibility design is an important consideration let web developers in their own code define your own "plug - in" module. This with the original included relation is different, can join his definitions of how components. Website program development never so simple. Security Windows based certification technology and every application configuration, you can ensure that your original procedures are absolutely safe. grammar in the very great degree with ASP compatible, and it offers a new programming model and structure, it can create a loft and stability better applications, and provide a better security protection. Can pass in existing ASP application gradually add function, at any time enhancement ASP application function. is an already compiled, based on environment, based on general language program in the server. A program in the server's first run, compile than ASP instant explanation program to a lot faster speed and can use compatible with the languages (including Visual , using c # and .) creation applications. In addition, any application can be used throughout Framework. Developers can conveniently to obtain these technical advantages, including custody of the common language runtime type safety, environment, inherit, etc. can seamlessly with WYSIWYG HTML editor and other programming tools (including Microsoft Visual ) work together. This not only make the Web development more convenient, but also can provide these tools must provide all the advantages, including developers can be used to will server controls drag-and-drop Web page GUI and fully integrated debugging support. When creating application, the developers can use Web form or XML Web services for, or in any way they deem fit combined. Each function can get the same structural support, make you can use identity verification scheme, the cache often use of data, or for application configuration for custom. If you have never development of a Web site procedures, so it's not for you, you should at least master some HTML language and simple Web development terms (but I believe if interested can be quickly grasp). You don't need to previous ASP development experience (of course experienced better),but you must understand interactive Web application development concepts, ranging form, the script, and data interface concept, if you have these conditions, then you can be in world begins to soar. is not only the Active Server brief (ASP) next version, and is a built in common language program structure that can be used to a Web Server to build a powerful Web applications. provides many Web development mode than now great advantage. operation framework is divided into several stages: With the Web server in IIS news flow stage. page in the news dispatch. page in the message handling. original design conception, is to make the developer as VB development tool that can use event-driven type program development mode (-) - Driven to Model the method to develop web pages with application, if want to use ASP technology to achieve this jop, use must use a large number of ancillary information, such as the query string or form field data to identify and judge the object of source, Event flow and the called function, etc., need to write code is quite, but very ingenious use of form fields and JavaScript scripts to events hidden transfer Model.In when run, there are often web round-trip action (round - trip), in the called picker, in in traditional ASP technology, judge web of back is needed by developers themselves to write, , developers can use brief. IsPostBack function to judge whether for first run (when found HTTP POST requirement of data is null), it will ensure that controls events will only run again, but it has a shortcoming (based on HTTP POST, the defect), is when the user use the browser's renovatesthe function (hit F5 or refresh button) refresh web, the last time running events will be run again, if we are to avoid this situation, must want to force the browser cache can empty.State management (state management) in Web applications, it is always very important topic, good condition management to help developers to develop with state to sustain the applications (such as work flow type Application or e-commerce applications), but state management function may view Application status and thedeployment of information sharing degree chooses in , divided into the server configuration management and client state management, client state management for ViewState and Cookies, server Session state management is to apply object. Their cultures depends on: ViewState is encrypted data streams, and HTML together the output to client. Cookies are encrypted (also don't encryption) of small data, and HTML is different, it can high-speed slow existing client browser. Is the server Session state preservation mechanism, each client all have independent space (in browsers run individual to fu with only SessionID values). Apply is server-side state preservation mechanism, but the client Application all Shared one state data.State management in a single server, can be stored in the server's memory, but if in the large-scale Web site, use a lot of Web server to implement the Load balance (-) processing, Load there will be stored in the state where on the problem, so it needs a can in every Web server storage medium between state, such as independent servers or database, etc. In in support of four state storage medium: InProc: storage and the same operation process (state) procedure in -, suitable for a single server status of storage. StateServer: storage in state server (state server), suitable for cross-server state storage, but because it USES communication port, so in use should be paid attention to the firewall problem. SQLServer: stored in separate SQL Server database, suitable for cross-server state storage. Custom: on the realization of state provider (state provider).Database ManagementDatabase records and files must be organized to allow retrieval of the information. Early system were arranged sequentially (i.e., alphabetically, numerically, or chronologically); the development of direct-access storage devices made possible random access to data via indexes. Queries are the main way users retrieve database information. Typically the user provides a string of characters, and the computer searches the database for a corresponding sequence and provides the source materials in which those characters appear. A user can request, for example, all records in which the content of the field for a person’s last name is the word Smith.The many users of a large database must be able to manipulate the informationwithin it quickly at any given time. Moreover, large business and other organizations tend to build up many independent files containing related and even overlapping data, and their data, processing activities often require the linking of data from several files. Several different types of database management systems have been developed to support these requirements: flat, hierarchical, network, relational, and object-oriented.In flat databases, records are organized according to a simple list of entities; many simple databases for personal computers are flat in structure. The records in hierarchical databases are organized in a treelike structure, with each level of records branching off into a set of smaller categories. Unlike hierarchical databases, which provide single links between sets of records at different levels, network databases create multiple linkages between sets by placing links, or pointers, to one set of records in another; the speed and versatility of network databases have led to their wide use in business. Relational databases are used where associations among files or records cannot be expressed by links; a simple flat list becomes one table, or “relation”, and multiple relations can be mathematically associated to yield desired information. Object-oriented databases store and manipulate more complex data structure s, called “objects”, which are organized into hierarchical classes that may inherit properties from classes higher in the chain; this database structure is the most flexible and adaptable.The information in many databases consists of natural-language texts of documents; number-oriented database primarily contain information such as statistics, tables, financial data, and raw scientific and technical data. Small databases can be maintained on personal-computer systems and may be used by individuals at home. These and larger databases have become increasingly important in business life. Typical commercial applications include airline reservations, production management, medical records in hospitals, and legal records of insurance companies. The largest databases are usually maintained by governmental agencies, business organizations, and universities. These databases may contain texts of such materials as catalogs of various kinds. Reference databases contain bibliographies or indexes that serve as guides to the location of information in books, periodicals, and other publishedliterature. Thousands of these publicly accessible databases now exist, covering topics ranging from law, medicine, and engineering to news and current events, games, classified advertisements, and instructional courses. Professionals such as scientists, doctors, lawyers, financial analysts, stockbrokers, and researchers of all types increasingly rely on these databases for quick, selective access to large volumes of information.DBMS Structuring TechniquesSequential, direct, and other file processing approaches are used to organize and structure data in single files. But a DBMS is able to integrate data elements from several files to answer specific user inquiries for information. That is, the DBMS is able to structure and tie together the logically related data from several large files.Logical Structures. Identifying these logical relationships is a job of the data administrator. A data definition language is used for this purpose. The DBMS may then employ one of the following logical structuring techniques during storage access, and retrieval operations.List structures. In this logical approach, records are linked together by the use of pointers. A pointer is a data item in one record that identifies the storage location of another logically related record. Records in a customer master file, for example, will contain the name and address of each customer, and each record in this file is identified by an account number. During an accounting period, a customer may buy a number of items on different days. Thus, the company may maintain an invoice file to reflect these transactions. A list structure could be used in this situation to show the unpaid invoices at any given time. Each record in the customer in the invoice file. This invoice record, in turn, would be linked to later invoices for the customer. The last invoice in the chain would be identified by the use of a special character as a pointer.Hierarchical (tree) structures. In this logical approach, data units are structured in multiple levels that graphically resemble an “upside down” tree with the root at the top and the branches formed below. There’s a superior-subordinate relationship in a hierarchical (tree) structure. Below the single-root data component are subordinateelements or nodes, each of which, in turn, “own” one or more other elements (or none). Each element or branch in this structure below the root has only a single owner. Thus, a customer owns an invoice, and the invoice has subordinate items. The branches in a tree structure are not connected.Network Structures. Unlike the tree approach, which does not permit the connection of branches, the network structure permits the connection of the nodes in a multidirectional manner. Thus, each node may have several owners and may, in turn, own any number of other data units. Data management software permits the extraction of the needed information from such a structure by beginning with any record in a file.Relational structures. A relational structure is made up of many tables. The data are stored in the form of “relations” in these tables. For example, relation tables could be established to link a college course with the instructor of the course, and with the location of the class.To find the name of the instructor and the location of the English class, the course/instructor relation is searched to get the name (“Fitt”), and the course/location relation is a relatively new database structuring approach that’s expected to b e widely implemented in the future.Physical Structures. People visualize or structure data in logical ways for their own purposes. Thus, records R1 and R2 may always be logically linked and processed in sequence in one particular application. However, in a computer system it’s quite possible that these records that are logically contiguous in one application are not physically stored together. Rather, the physical structure of the records in media and hardware may depend not only on the I/O and storage devices and techniques used, but also on the different logical relationships that users may assign to the data found in R1and R2. For example, R1 and R2 may be records of credit customers who have shipments send to the same block in the same city every 2 weeks. From the shipping department manager’s perspective, then, R1 and R2 are sequential entries on a geographically organized shipping report. But in the A/R application, the customers represented by R1 and R2 may be identified, and their accounts may be processed,according to their account numbers which are widely separated. In short, then, the physical location of the stored records in many computer-based information systems is invisible to users.。
