- Functional requirements
In
software engineering , a functional requirement defines a function of asoftware system or its component. A function is described as a set of inputs, the behavior, and outputs (see also ).Functional requirements may be calculations, technical details, data manipulation and processing and other specific functionality that show "how" a
use case is to be fulfilled. They are supported by non-functional requirements, which impose constraints on the design or implementation (such as performance requirements, security, or reliability).As defined in requirements engineering, functional requirements specify particular behaviors of a system. This should be contrasted with non-functional requirements which specify overall characteristics such as cost and
reliability . Typically, a requirements analyst generates functional requirements after buildinguse case s. However, this may have exceptions since software development is an iterative process and sometimes certain requirements are conceived prior to the definition of the use cases. Both artifacts (use cases documents and requirements documents) complement each other in a bidirectional process.Process
A typical functional requirement will contain a unique name and number, a brief summary, and a rationale. This information is used to help the reader understand why the requirement is needed, and to track the requirement through the development of the system.
The crux of the requirement is the description of the required behavior, which must be clear and readable. The described behavior may come from organizational or business rules, or it may be discovered through elicitation sessions with users, stakeholders, and other experts within the organization. Many requirements may be uncovered during the use case development. When this happens, the requirements analyst should create a placeholder requirement with a name and summary, and research the details later, to be filled in when they are better known.
Software requirements must be clear, correct, unambiguous, specific, and verifiable.
Books
*cite book
first = Karl E.
last = Wiegers
authorlink =
year = 2003
title = Software Requirements 2: Practical techniques for gathering and managing requirements throughout the product development cycle
edition = 2nd ed.
publisher = Microsoft Press
location = Redmond
id = ISBN 0-7356-1879-8
url = http://processimpact.com/pubs.shtml#reqs
*cite book
author = Andrew Stellman and Jennifer Greene
authorlink =
year = 2005
title = Applied Software Project Management
edition =
publisher = O'Reilly Media
location = Cambridge, MA
id = ISBN 0-596-00948-8
url = http://www.stellman-greene.com/
*cite book
author = Ian Sommerville
authorlink = Ian Sommerville
year = 2006
title = Software Engineering
edition = 8th ed.
id = ISBN 0-321-31379-8
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