【正文】 task. Finally, conditions change, and a program must be updated。s major functions and data elements me thodically. Remember that the objective is translating user needs into technical terms. Since the system starts with the user, the first step is defining the user39。 because the program is but one ponent in a system. A system is a group of ponents that work together to acplish an objective. For example, consider a payroll system. Its objective is paying employees. What ponents are involved? Each day， employees record their hours worked on time cards. At the end of each week, the time cards are collected and delivered to the puter center, where they are read into a payroll program. As it runs, the progra m accesses data files. Finally, the paychecks are printed and distributed. For the system to work, people, procedures, input and output media, files, hardware, and software must be carefully coordinated. Note that the program is but one ponent in a system. Computerbased systems are developed because people need information. Those people, called users, generally know what is required, but may lack the expertise to obtain it. Technical professionals, such as programmers, have the expertise, but may lack training in the user39。s 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 for graphically describing these data flows. Four symbols are used (Fig. 1). Data sources and destinations are represented by squares。 a good analyst will develop several feasible alternatives before choosing one. Fig 4 The flowchart maps the system, highlighting its major physical ponents. Since the data link the ponents, the next task is defining the data structures. 7 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 file39。被稱為用戶的那些人常常知道需求什么信息，但是他們可能缺乏得到這些信息的計(jì)算機(jī)的專門知識(shí)。注意，當(dāng)這個(gè)過程開始時(shí)，用戶擁有很重要的資料，分析員必須認(rèn)真地聽和學(xué)。店主希望有選擇地查看供應(yīng)中任意一種短缺商品的清單，如果合理的話，定貨補(bǔ)充庫存，因此系統(tǒng)必須能和經(jīng)營管理部門對(duì)話。從數(shù)據(jù)的目的地 SUPPLIEF 開始。例如，如果分析員沒有足夠的信息使數(shù)據(jù)字典的條目完整化，那么分析員就可能丟失一些內(nèi)容。因?yàn)閿?shù)據(jù)鏈接了部件，所以接下來的工作就是確定數(shù)據(jù)結(jié)構(gòu)。注意，程序在系統(tǒng)的意義上被定義和規(guī)劃。我要誠摯地感謝我的母校對(duì)我五年的培育。 此文章出自： 華北電力大學(xué)科技學(xué)院 信管 08K1 學(xué)生 081906040119 16 致 謝 在整個(gè)畢業(yè)設(shè)計(jì)過程中，我得到了指導(dǎo)老師和實(shí)習(xí)單位的大力支持， 在此，特別感謝各位老師、實(shí)習(xí)單位的各位老師以及我的同學(xué)們。一種可能的系統(tǒng)是當(dāng)事務(wù)一發(fā)生就接收并處理該事務(wù)；另一種可供選擇的方案是可整天的收集銷售單，商店關(guān)門以后，成批地處理。 請(qǐng)看系統(tǒng)流程圖，它指明了若干硬部件，其中包括一臺(tái)計(jì)算機(jī)、一個(gè)磁盤驅(qū)動(dòng)器、一個(gè)數(shù)據(jù)輸入終端、一臺(tái)打印機(jī)和一個(gè)顯示終端等；還需要兩個(gè)程序，事務(wù)處理程序和報(bào)告與再定貨程序；除了硬件和程序以外，我們還需要貨單文件以及 I/O 設(shè)備與軟件之間數(shù)據(jù)流的數(shù)據(jù)結(jié)構(gòu) 。這是該階段的基本要求。 GENERATEREORDER（產(chǎn)生訂貨單程序）就向 SUPPLIER（供應(yīng)商）發(fā)出需要的數(shù)據(jù)，供應(yīng)商就把貨運(yùn)送到商店。在分析階段礙到了這方面知識(shí)，并正式地形成文件。 麻煩的是，隨著顧客的購買庫存減少了，還有退貨以及追加訂貨等情況，所以貨物的清單經(jīng)常地發(fā)生變化．店主喜歡按貨物清單購銷，剛好在商店售完某種10 貨物之前，再訂購這種貨。最后，打印出工資單，用來分發(fā)。 how might they be implemented? One possibility is writing one program for each process. Another is bining two or more processes in a single program。 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 system39。s 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 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 term. The idea is to ensure that both the user and the analyst are thinking about the same thingThus, a clear, written statement expressing the analyst39。s understanding of the system requirements. By reviewing these documents, the user can correct misunderstandings or oversights. Finally, they represent an excellent starting point the next step, design. 23 Design As we enter the design stage, we know what the system must do, and thus can begin thinking about how to do it