1、I 附录 1 外文翻译 (原文 ) Systems Analysis and Design Working under control of a stored program, a computer processes data into information. Think about that definition for a minute. Any given computer application involves at least three components: hardware, software, and data. Merely writing a program isn
2、t enough； because the program is but one component in a system. A system is a group of components that work together to accomplish an objective. For example, consider a payroll system. Its objective is paying employees. What components are involved? Each day， employees record their hours worked on t
3、ime cards. At the end of each week, the time cards are collected and delivered to the computer center, where they are read into a payroll program. As it runs, the program accesses data files. Finally, the paychecks are printed and distributed. For the system to work, people, procedures, input and ou
4、tput media, files, hardware, and software must be carefully coordinated. Note that the program is but one component in a system. Computer-based systems are developed because people need information. Those people, called users, generally know what is required, but may lack the expertise to obtain it.
5、 Technical professionals, such as programmers, have the expertise, but may lack training in the users field. To complicate matters, users and programmers often seem to speak different languages, leading to communication problems. A systems analyst is a professional who translates user needs into tec
6、hnical terms, thus serving as a bridge between users and technical professionals. Like an engineer or an architect, a systems analyst solves problems by combining solid technical skills with insight, imagination, and a touch of art. Generally, the analyst follows a well-defined, methodical process t
7、hat includes at least the following steps； 1.Problem definition 2.Analysis 3.Design 4.Implementation 5.Maintenance 2 At the end of each step, results are documented and shared with both the user and the programmers. The idea is to catch and correct errors and misunderstandings as early as possible.
8、Perhaps the best way to illustrate the process is through example. Picture a small clothing store that purchases merchandise at wholesale, displays this stock, and sells it to customers at retail. On the one hand, too much stock represents an unnecessary expense. On the other hand, a poor selection
9、discourages shoppers. Ideally, a balance can be achieved: enough, but not too much. Complicating matters is the fact that inventory is constantly changing, with customer purchases depleting stock, and returns and reorders adding to it. 1 The owner would like to track inventory levels and reorder and
10、 given item just before the store runs out. For a single item, the task is easy-just count the stock-on-hand. Unfortunately, the store has hundreds of different items, and keeping track of each one is impractical. Perhaps a computer might help. 2-1 Problem Definition The first step in the systems an
11、alysis and design process is problem definition. The analysts objective is determining what the user (in this case, the stores owner) needs. Note that, as the process begins, the user possesses the critical information, and the analyst must listen and learn. Few users are technical experts. Most see
12、 the computer as a magic box, and are not concerned with how it works. At this stage, the analyst has no business even thinking about programs, files, and computer hardware, but must communicate with the user on his or her own term. The idea is to ensure that both the user and the analyst are thinki
13、ng about the same thing-Thus, a clear, written statement expressing the analysts understanding of the problem is essential. The user should review and correct this written statement. The time to catch misunderstandings and oversights is now, before time, money and effort are wasted. Often, following
14、 a preliminary problem definition, the analyst performs a feasibility study. The study a brief capsule version of the entire systems analysis and design process, attempts to answer three questions: 1.Can the problem be solved? 2.Can it be salved in the users environment? 3.Can it be solved at a reas
15、onable cost? If the answer to any one of these questions is no, the system should not be developed. Given a good problem definition and a positive feasibility study, the 3 analyst can turn to planning and developing a problem solution. 2- 2 Analysis As analysis begins, the analyst understands the pr
16、oblem. The next step is determining what must be done to solve it. The user knows what must be done 1 during analysis； this knowledge is extracted and formally documented. Most users think in terms of the functions to be performed and the data elements to be manipulated. The objective is to identify
17、 and link these key functions and data elements, yielding a logical system design. Start with the systems basic functions. The key is keeping track of the stock-on-hand for each product in inventory. Inventory changes because customers purchase, exchange, and return products, so the system will have
18、 to process customer transactions. The stores owner wants to selectively look at the inventory level for any product in short supply and, if appropriate, order replacement stock, so the system must be able to communicate with management. Finally, following management authorization, the system should
19、 generate a reorder ready to send to a supplier. Fig 1 Given the systems basic functions, the analysts next task is gaining a sense of their logical relationship. A good way to start is by describing how data flow between the functions. As the name implies, data flow diagrams are particularly useful
20、 for graphically describing these data flows. Four symbols are used (Fig. 1). Data sources and destinations are represented by squares； input data enter the system from a source, and output data flow to a destination. Once in the system, the data are manipulated or change by processes, represented b
21、y round-corner rectangles. A process might be a program, a procedure, or anything else that changes or moves data. Data can be held for later processing in data stores, symbolized by open-ended rectangles. A data store might be a disk file, a tape file, a database, written notes, or even a persons memory.
