TAILIEUCHUNG - Software Engineering For Students: A Programming Approach Part 15

Software Engineering For Students: A Programming Approach Part 15. This fully revised version of Doug Bell's Software Engineering: A Programming Approach continues to use the successful formula of the previous editions. The author's approach is to present the main principles, techniques and tools used in software engineering, one by one, chapter by chapter. This book is a unique introduction to software engineering for all students of computer science and its related disciplines. It is also ideal for practitioners wishing to remain current with new developments in the area | 118 Chapter 9 Data flow design Figure Converting raw data for input In general a piece of software will require that several transformations are carried out on its input data streams and that after the main processing several transformations are carried out on its output data streams. We can use an analogy from outside computing. To make wine we have first to grow vines pick the grapes transport them to the farm and then press them. Only then can we carry out the central task of fermentation. After this we have to pour the wine into bottles store the bottles for some time and finally transport them to the shop. Data flow design recognizes this as the archetypal structure for software systems. As we have seen data flow design concentrates on modeling the flows of data within software. The essential ingredient is any application in which the flows of data are important and can be identified easily. Data flows are significant because nearly every software system involves data flows. In all computer systems information enters the computer as a serial stream of data simply because time flows serially. Similarly any component within a software system is only capable of carrying out one task at any time. Thus the demands placed on any component are a serial data stream. Therefore data flows constitute a fundamental concept within software. Summary Data flow design proceeds by initially analyzing the data flows and transformations within a software system. The first task is to draw the data flow diagram bubble diagram consisting of arcs data flows and bubbles transformations . This diagram can be arrived at by using any one of the following three methods 1. starting with a single large bubble break it up into smaller bubbles 2. start with the output data stream from the software and trace it backwards 3. start with the input data stream to the system and trace it forwards. Exercises 119 During the second stage of data flow design the data flow diagram is transformed .

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