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Fundamentals of Software Engineering: Requirements Engineering Overview

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  1. CSC-3324: Chapter 4 Title: What is a requirement? Mandatory reading: Sommerville 6, 7th ed., Chap.: 7

  2. Software engineering is concerned with theories, methods and tools for professional software development Maintainability, Dependability, Efficiency, Usability Wrap up on Chap. 1, 2 & 3... Understandable, Visible, Supported, Accepted, Reliable, Rapid, etc. A quick and cheap study of the project requirements in order to assess the business opportunity, the technology enablers and the schedule... • Component-based development • The system is assembled from • existing components • The waterfall model • Separate and distinct phases • of specification and • development • Prototyping development • Specification and development • are interleaved Structured set of activities (steps) required to develop a software system.... • What isSoftware Engineering (SE) ? • The major goal of SE is to produce good software cost effectively… What is good software? • In order to produce good software, we need to follow a good SE process… What is a good process? • Some SE process models are widely used and universally recognized… • Before launching any SE process, we should first be perform a feasibility study...

  3. Requirements Engineering... • The process of establishing the services that the customer requires from a system and the constraintsunder 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…. • Engineering consists of collecting, analyzing and documenting the requirements in order to better understand/Present them...

  4. What is a requirement? • An attribute that the projected system must fulfill… • It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification. • Examples… • The word Requirement is not uniformly used...

  5. Some common problems... • Precision... • Completeness... • Consistency...

  6. Types of requirements... • User requirements • Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers… (Usually during the Feasibility study…) • Information system requirements • A structured document setting out detailed descriptions of the system services. Written as a contract between client and contractor(Usually during the Req. Eng.…) • Software specification • A detailed software description which can serve as a basis for a design or implementation. Written for developers (Design)

  7. Functional and non-functional requirements • Functional requirements • Non-functional requirements • Domain requirements • Requirements that come from the application domain of the system and that reflect characteristics of that domain

  8. Functional requirements • Statements of services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations. • 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

  9. Non-functional requirements • Constraints on the services or functions offered by the system such as timing constraints, constraints on the development process, standards, etc. • Constraints are I/O device capability, system representations, etc. • Reliability, Response time and Storage requirements. • Mandating CASE system, programming language or development method

  10. Domain requirements • Derived from the application domain and describe system characteristics and features that reflect the domain • May be new functional requirements, constraints on existing requirements or define specific computations • If domain requirements are not satisfied, the system may be unworkable

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