软件工程Chapter 04 requirement engineering.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * 4.3.1 Natural language specification Natural language has been used to write requirements for software since the beginning of software engineering. It is expressive, intuitive, and universal. To minimize misunderstandings Invent a standard format and ensure that all requirement definitions adhere to that format. Use language consistently to distinguish between mandatory and desirable requirements. Use text highlighting (bold, italic, or color) to pick out key parts of the requirement. Do not assume that readers understand technical software engineering language. Whenever possible, you should try to associate a rationale with each user requirement. 4.3.2 Structured specification Structured natural language is a way of writing system requirements where the freedom of the requirements writer is limited and all requirements are written in a standard way. This approach maintains most of the expressiveness and understandability of natural language but ensures that some uniformity is imposed on the specification. Structured language notations use templates to specify system requirements. A example Structured forms When a standard form is used for specifying functional requirements, the following information should be included: A description of the function or entity being specified. A description of its inputs and where these come from. A description of its outputs and where these go to. Information about the information that is needed for the computation or other entities in the system that are used. A description of the action to be taken. If a functional approach is used, a pre-condition setting out what must be true before the function is called, and a post-condition specifying what is true after the function is called. A description of the side effects (if any) of the operation. Structured forms To use a structured approach to specifying system requirements, you define one or more sta