外文翻譯----系統(tǒng)的分析與設(shè)計(jì)-其他專業(yè)(編輯修改稿)
2025-02-24 09:13 本頁面
【文章內(nèi)容簡介】 formation, and the analyst must listen and learn. Few users are technical experts. Most see the puter 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 puter hardware, but must municate with the user on his or her own terms. The idea is to ensure that both the user and the analyst are thinking about the same thing. Thus, a clear, written statement expressing the analyst’s 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 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 solved in the user’s environment? 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. Analysis As analysis begins, the analyst understands the problem. The next step is determining what must be done to solve it. The user knows what must be done。 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 and link these key functions and data elements, yielding a logical system design. Start with the system’s basic functions. The key is keeping track of the stockonhand for each product in inventory. Inventory changes because customers purchase, exchange, and return products, so the system will have to process customer transactions. The store’s 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 municate with management. Finally, following management authorization, the system should generate a reorder ready to send to a supplier. Given the system’s basic functions, the analyst’s next task is gaining a sense of their logical relation. A good way to start is by describing how data flow between the functions. As the name implies, data flow diagrams are particularly useful for graphically describing these data flows. Four symbols are used. Data sources and destinations are represented by squares。 input data enter the system form a source, and output data flow to a destination. Once in the system, the data are manipulated or changed by processes, represented by roundcorner 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 openended rectangles. A data store might be a disk file, a tape file, a database, written notes, or even a person’s memory. Finally, data flow between sources, destinations, processes, and data stores over data flows, which are represented by arrows. Preliminary data flow diagram for the inventory system. Start a CUSTOMER. Transactions flow from a customer into the system, where they are handled by Process transaction. A data store, the 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 necessary, requesting a recorder. 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 flow diagram describes the logical system. The next step is tracing the data flow. Start with the destination SUPPLIER. Reorders flow to suppliers
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