Ch-4 - Software Requirements Objectives To introduce the concepts of user and system requirements To describe functional and non-functional

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Software Requirements
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To introduce the concepts of user and system requirements To describe functional and non-functional requirements To explain how software requirements may be organised in a requirements document Objectives
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What is a requirement? It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification.
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Requirements engineering The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed. The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process.
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Types of requirement User requirements Statements in natural language plus diagrams of the services, the system provides and its operational constraints. Written for customers. System requirements A structured document setting out detailed descriptions of the system’s functions, services and operational constraints. Defines what should be implemented. contract between client and contractor.
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A Software Design Specification It is an abstract description of the software design which is a basis for more detailed design implementation. This specification adds further detail to the system requirements specification.
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Functional and Non-Functional requirements Functional requirements Non-functional requirements Domain requirements
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Functional requirements Describe functionality or system services. Depend on the type of software, expected users and the type of system where the software is used. Functional user requirements may be high- level statements of what the system should do, but functional system requirements should describe the system services in detail.
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The LIBSYS system A library system that provides a single interface to a number of databases of articles in different libraries. Users can search for, download and print these articles for personal study.
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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.
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Requirements imprecision Problems arise when requirements are not precisely stated. Ambiguous requirements may be interpreted in different ways by developers and users.
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Requirements completeness and consistency In principle, requirements should be both complete and consistent.
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This note was uploaded on 02/23/2012 for the course CS 101 taught by Professor Martand during the Spring '10 term at Punjab Engineering College.

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Ch-4 - Software Requirements Objectives To introduce the concepts of user and system requirements To describe functional and non-functional

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