SoftwareRequirements摘要.pptVIP

Software Requirements Descriptions and specifications of a system Objectives To introduce the concepts of user and system requirements To describe functional and non-functional requirements To explain two techniques for describing system requirements To explain how software requirements may be organised in a requirements document Topics covered 5.1 Functional and non-functional requirements 5.2 User requirements 5.3 System requirements 5.4 The software requirements document Requirements engineering Determine services that the customer requires and the constraints on system and its development Requirements - system services and constraints What is a requirement? High-level abstract statement of service /constraint ? detailed mathematical functional specification Term “Requirements” is “overloaded” High description for contractor to bid Detailed description of system to be delivered Requirements abstraction (Davis) Types of requirement User requirements System requirements Software specification Definitions and specifications Requirements readers Functional and non-functional requirements Functional requirements Non-functional requirements Domain requirements Functional requirements Describe functionality or system services Functional user requirements - high-level statements of what the system should do Functional system requirements - describe the system services in detail Examples of functional requirements The user shall be able to search either all of the initial set of databases or select a subset from it. The system shall provide appropriate viewers for the user to read documents in the document store. Every order shall be allocated a unique identifier (ORDER_ID) which the user shall be able to copy to the account’s permanent storage area. Requirements imprecision Problems when requirements not precisely stated E.g. the term ‘appropriate viewers’ E.g. does “see” mean on screen or on paper Requirements completeness and consistency In principle require