ch5 - ©Ian Sommerville 2000 Software Engineering 6th...

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Unformatted text preview: ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 1 Software Requirements l Descriptions and specifications of a system ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 2 Objectives l To introduce the concepts of user and system requirements l To describe functional and non-functional requirements l To explain two techniques for describing system requirements l To explain how software requirements may be organised in a requirements document ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 3 Topics covered l Functional and non-functional requirements l User requirements l System requirements l The software requirements document ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 4 Requirements engineering l The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed l The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 5 What is a requirement? l It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification l This is inevitable as requirements may serve a dual function • May be the basis for a bid for a contract - therefore must be open to interpretation • May be the basis for the contract itself - therefore must be defined in detail • Both these statements may be called requirements ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 6 Requirements abstraction (Davis) “If a company wishes to let a contract for a large software development project, it must define its needs in a sufficiently abstract way that a solution is not pre-defined. The requirements must be written so that several contractors can bid for the contract, offering, perhaps, different ways of meeting the client organisation’s needs. Once a contract has been awarded, the contractor must write a system definition for the client in more detail so that the client understands and can validate what the software will do. Both of these documents may be called the requirements document for the system.” ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 7 Types of requirement l User requirements • Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers l System requirements • A structured document setting out detailed descriptions of the system services. Written as a contract between client and contractor l Software specification • A detailed software description which can serve as a basis for a design or implementation. Written for developers ©Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 5 Slide 8 Definitions and specifications...
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This note was uploaded on 11/09/2009 for the course SE 120336 taught by Professor Unknown during the Spring '09 term at Avila University.

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ch5 - ©Ian Sommerville 2000 Software Engineering 6th...

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