【正文】 d 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。 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。 thus, product and reorder quantities must be stored in STOCK. Other data elements, such as purchased and 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 –onhand for a given item is an example of a data element generated by an algorithm in one of the procedures. Step by step, methodically, 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 puterized data dictionaries have bee 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’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 user’s needs. Users think in terms of functions and data. They do not visualize programs, or files, or hardware, 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 d