Requirements EngineeringLesson 2

Terminologies: Software Acquisition is where requirement

engineering significantly meets business strategy.

Software Requirements are description of features and functionalities of the target system.

Requirements are description of the services that a software must provide and the constraints under which it must operate.

Requirements convey the expectations of users from the software product. The requirements can be obvious or hidden, known or unknown, expected or unexpected from client’s point of view.

Types of Requirements User requirements

Statements in natural language plus diagrams of the services that the systems provides and its operational constraints.

Written for customers System requirements

A structured document setting out detailed descriptions of the system services

Written as a contract between client and contractor Software Specifications

A detailed description which can serve as a basis for a design or implementation

Written for developers

Functional and non-functional requirements

Functional Requirements Statements of services that the system should

provide, how the system should react to particular inputs and how the system should behave in particular situations

Describe functionality or system services Depend on the type of software, expected users

and the and the type of system where the software is used.

Functional user requirements may be high-level statements of what the system should do; it should describe the system services in detail.

Functional Requirements Examples: The user should 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 allocated a unique identifier (ORDER_ID) which the user shall be able to copy to the account’s permanent storage area.

Non-functional Requirements Constraints on the services or functions

offered by the system such as timing constraints, constraints on the development process, standards, among others.

It can be categorized as product requirements, organisational requirements, and external requirements.

Non-functional Requirements

Product Requirements Requirements which specify that the

delivered product must behave in a particular way

Portability, reliability, usability, efficiency – space & performance

Organisational Requirements Requirements which are a consequence of

organisational policies and procedures Delivery, implementation and standards

Non-functional Requirements External Requirements

Requirements which arises from factors which are external to the system and its development process

Ethical, interoperability, legislative (safety & privacy)

Requirement Engineering The process to gather software

requirements from client, analyze and document them is known as Requirement Engineering

The goal of requirement engineering is to develop and maintain sophisticated and descriptive ‘System Requirements Specification’ document.

Requirement Engineering Process

1. Feasibility Study2. Requirements Gathering3. Software Requirement Specification4. Software Requirement Validation

1. Feasibility Study Feasible – possible, achievable, practical.

1. When the client approaches the organizaiton for getting the desired product,

2. the analysts does a detailed study whether the system and its functionality are feasible to develop.

FS is focused towards goal of the organization. It also explores technical aspects of the project and product such as usability, maintainability, productivity and integration ability.

2. Requirement Gathering If the feasibility is positive towards

undertaking the project. Next phase starts with gathering

requirements from the user. Analysts and engineers communicate

with the client and end-users to know their ideas on what the software should provide and which features they want the software to include.

3. Software Requirement Specification SRS is a document created by system

analysts after the requirements are collected from various stakeholders.

The requirements received from a client are written in natural language.

It is the responsibility of system analyst to document the requirements in technical language so that they can comprehend and useful by the software development team.

SRS should come up with following features:1. User Requirements are expressed in natural

language.2. Technical requirements are expressed in

structured language, which is used inside the organization.

3. Design description should be written in pseudo code

4. Format forms and GUI screens prints5. Conditional and mathematical notations for

DFDs etc.

4. Software Requirement Validation After SRS are developed, the requirements

mentioned in this document are validated. User might ask for illegal, impractical solutions or

experts may interpret the requirements incorrectly. – Costly.

It can be checked against following conditions. If they can be practically implemented If they are valid and as per functionality and domain of

software If there any ambiguities (doubts) If they are complete If they can be demonstrated

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