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1、信息系统毕业论文中英文资料对照外文翻译信息系统毕业论文中英文资料对照外文翻译 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
2、data. Merely writing a program isnt 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，employe
3、es record their hours worked on time 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,
4、 people, procedures, input and output 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
5、 lack the expertise to obtain it. 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 w
6、ho translates user needs into technical 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 w
7、ell-defined, methodical process that includes at least the following steps; 1.Problem definition I 2.Analysis 3.Design 4.Implementation 5.Maintenance 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 misunde
8、rstandings as early as possible. 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
9、the other hand, a poor selection 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
10、 inventory levels and reorder and 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
11、 The first step in the systems analysis 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 user
12、s are technical experts. Most see 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 th
13、e user and the analyst are thinking 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 ef
14、fort are wasted. Often, following 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 2.Can it be salved in the users enviro
15、nment? 3.Can it be solved at a reasonable 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 analyst can turn to planning and developing a problem solution. 2- 2 Analysis As analysis begin
16、s, the analyst understands the problem. 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 manipula
17、ted. The objective is to identify 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
18、products, so the system will have 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
19、 authorization, the system should 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
20、 diagrams are particularly useful 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 3
21、 change by processes, represented by 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,
22、 written notes, or even a persons memory. Finally, data flow between sources, destinations, processes, end data stores over data flows, which are represented by arrows. Fig 2 Figure 2 shows a preliminary data flow diagram for the inventory system. Start with CUSTOMER. Transactions flow from a custom
23、er f into the system, where they are handled by Process transaction. A data store, STOCK, holds data on each item in inventory. Process transaction changes the data to reflect the new transaction. Meanwhile, MANAGEMENT accesses the system through Communicate, evaluating the data in STOCK and, if nec
24、essary, requesting a reorder. Once, a reorder is authorized. Generate reorder sends necessary data to the SUPPLIER, who ships the items to the store. Note that, because the reorder represents a change in the inventory level of a particular product or products it is handled as a transaction. The data
25、 flow diagram describes the logical system. The next step is tracing the data flows. Start with the destination SUPPLIER. Reorders flow to suppliers; for example, the store might want 25 pairs of jeans. To fill the order, the supplier needs the product description and the reorder quantity. Where do
26、these data elements come from? Since they are output by Generate reorder, they must either be Input to or generated by this process. Data flow into Generate reorder for STOCK; thus, product descriptions and reorder quantities must be stored in STOCK. Other data elements, such as the item purchased a
27、nd the purchase quantity are generated by CUSTOMER. Still others, for example selling price and reorder point, are generated by or needed by MANAGEMENT. The current stock-on-hand for a 4 given item is an example of a data element generated by an algorithm in one of the procedures. Step by step, meth
28、odically, the analyst identifies the data elements to be input to .stored by, manipulated by, generated by, or output by the system. To keep track of the data elements, the analyst might list each one in a data dictionary. A simple data dictionary can be set up on index cards, but computerized data
29、dictionaries have become increasingly popular. The data dictionary, a collection of data describing and defining the data, is useful throughout the systems analysis and design process, and is often used to build a database during the implementation stage. The idea of analysis is to define the system
30、s major functions and data elements methodically. Remember that the objective is translating user needs into technical terms. Since the system starts with the user, the first step is defining the users needs. Users think in terms of functions and data. They do not visualize programs, or files, or ha
31、rdware .and during this initial, crucial analysis stage it is essential that the analyst think like a user, not like a programmer. Data flow diagrams and data dictionaries are useful tools. They provide a format for recording key information about the proposed system. Also, they jog the analysts mem
32、ory) for example, if the analyst doesnt have sufficient information to complete a data dictionary entry, he or she has probably missed something. Perhaps most importantly, the data flow diagram and the data dictionary document the analysts understanding of the system requirements. By reviewing these
33、 documents, the user can correct misunderstandings or oversights. Finally, they represent an excellent starting point the next step, design. 2-3 Design As we enter the design stage, we know what the system must do, and thus can begin thinking about how to do it. The objective is to develop a strateg
34、y for solving the problem. At this stage, we are not interested in writing code or in defining precise data structures; instead, we want to identify, at a black box level, necessary programs, files, procedures, and other components. The data flow diagram defines the systems necessary functions; how
35、might they be implemented? One possibility is writing one program for each process. Another is combining two or more processes in a single program; there are dozens of alternative solutions. Lets focus on one option and document it. A system flowchart uses symbols to represent programs, procedures,
36、hardware devices, and the other components of a physical system (Fig. 3). Our flowchart (.Fig. 5 4) shows that transaction data enter the system through a terminal, are processed by a data collection program, and then are stored on an inventory file. Eventually, the inventory file is processed by a
37、Report and reorder program. Through it, management manipulates the data and authorizes reorders. Fig. 4 on a system flowchart, symbols represent programs, procedures, hardware devices, and the other components of a physical system. Fig 3 Look at the system flowchart. It identifies several hardware c
38、omponents, including a computer, a disk drive, a data entry terminal, a printer, and a display terminal. Two programs are needed; Process transaction and Report and reorder. In addition to the hardware and the programs, well need data structures for the inventory file and for data flaws between the
39、I/O devices and the software. Note that this system flowchart illustrates one possible solution; a good analyst will develop several feasible alternatives before choosing one. 6 Fig 4 The flowchart maps the system, highlighting its major physical components. Since the data link the components, the n
40、ext task is defining the data structures. Consider, for example, the inventory file. It contains all the data elements from the data store STOCK. The data elements are listed in the data dictionary. Using them, the files data structure can be planned, How should the file be organized? That depends o
41、n how it will be accessed. For example, in some applications, data are processed at regular, predictable intervals. Typically, the data are collected over time and processed together, as a batch. If batch processing is acceptable, a sequential file organization is probably best. It is not always pos
42、sible to wait until a batch of transactions is collected, however. For example, consider an air defense early warning system. If an unidentified aircraft is spotted it must be identified immediately the idea of waiting until 5 _ 00 p.m. because thats when the air defense program is run is absurd. In
43、stead, because of the need for quick response, each transaction must be processed as it occurs. Generally such transaction processing systems call for direct access file. Our inventory system has two programs. One processes transactions. A direct access inventory file seems a reasonable choice. The
44、other allows management to study inventory data occasionally; batch processing would certainly do. Should the inventory file be organized sequentially or directly? Faced with such a choice a good analyst considers both options. One possible system might accept transactions and process them as they o
45、ccur. As an alternative, sales slips might be collected throughout the day and processed as a batch after the store closes. In the first system, the two programs would deal with direct access files; in the second system, they would be linked to sequential files. A program to process direct access da
46、ta is different from a program to process sequential data. The data drive the system. The choice of a data structure determines the programs structure. Note that the program is defined and planned in the context of the system. 2- 4 Implementation Once the systems major components have been identifie
47、d .we can begin to develop them. Our system includes two programs, several pieces of equipment, and a number of data structures. During implementation, each program is planned and written using the techniques described in Chapter 7. Files are created, and their 7 contents checked. New hardware is pu
48、rchased, installed, and tested. Additionally, operating procedures are written and evaluated. Once all the component parts are ready, the system is tested. Assuming the user is satisfied, the finished system is released. 2- 5 Maintenance Maintenance begins after the system is released. As people use it, they will suggest minor improvements and enhancements. Occasionally, bugs slip through debug and testing, and removing them is anoth
