云南农业大学计算机导论课件Chapter10 Software Engineering.pptVIP

10.1 SOFTWARE LIFE CYCLE A fundamental concept in software engineering is the software life cycle. Software, like many other products, goes through a cycle of repeating phase. By “obsolete,” we mean the software loses its validity because of inefficiency, obsolescence of the language, major change in the company, or other factors. Define the User A software package may be designed for a generic user or a specific user. The user of the package must be clearly defined. Define the Needs In this step, the best answer comes from the user. The user, or the representative of the user, clearly defines his/her expectations of the package. Define the Requirements Based on the needs of the user, the analyst can exactly define the requirements for the system. Define the Methods Finally, after the requirements are defined in clear terms, the analyst can choose the appropriate methods to meet those requirements. DESIGN PHASE The design phase defines how the system will accomplish what was defined in the analysis phase. In the design phase, the systems are determined, and the design of the files and/or the databases is completed. Modularity The whole package is divided into small modules. Each module is designed and tested and is linked to other modules through a main program. Tools The design phase uses several tools, the most common being a structure chart. A structure chart shows how to break your package into logical steps; each step is a separate module. The structure chart also shows the interaction between all the parts (modules). IMPLEMENTATION PHASE In this phase, you create the actual programs. Tools This phase uses several tools to show the logical flow of the programs before the actual writing of code. One tool, still popular, is the flowchart. A flowchart uses standard graphical symbols to represent the logical flow of data through a module. The second tool used by programmers i