Types of Specification

3.3.1

This presentation covers

• Types of specification:– Requirements specification– Design specification– System specification

and the differences between them.

Requirements Specification

• Developed by the systems analyst who has completed the feasibility and analysis stages of the systems life cycle.

• This specification is used explain what the system is supposed to do and how it will achieve this.

• It should also explain how the users will interact with the software.

Requirements Specification

• It should contain:– Functional requirements• What the users what the system to be able to do.• http://en.wikipedia.org/wiki/Functional_requirements

– Non-functional requirements• How the user wants the system to behave.• http://en.wikipedia.org/wiki/Non-functional_requirements

Requirements Specification• The contents of the requirements specification should also

include:– The purpose of the system.

• i.e. what are it’s objectives?

– Scope of the system.

– The proposed timescale of the system.

– End-user defined constraints including:• Budget• Time• hardware and software choices.

– A contract.

Scope of the System

• The events outside the system that cause the system to react.

• The actors outside the system that interact with the system.

• The information that flows between the system and the actors outside the system.

• The major functions included in the system.

• The user population.

Design Specification• Created by the system’s designer.

• The contents of the design specification will be different depending on what type of system is being created.– For example, a spreadsheet needs to contain

designs for formulas whereas a website needs to contain information about how pages are linked.

• There might be some similar design aspects to take on board though…– Data input forms might need to be designed?

Design Specification

• The contents should include:– The purpose of the system– Assumptions, limitations and

constraints– Inputs and Outputs

• Documents and screens/interface

– Error messages– Styles

• Colours, font sizes, house style etc

– Validation rules

Design Specification

• The contents should include:– Processing requirements/queries– Data structures– Modelling diagrams

• DFDs, ERDs, STDs

– Hardware– Software/programming language to

be used– Test plan

System Specification

• This specification defines the requirements of the system including:– Operational requirements:

• What operations should the system carry out?

– Information requirements:• What information should be provided to the end-users?

– Volume requirements:• How much processing will the system have to handle.

System Specification

• This specification defines the requirements of the system including:

– General system requirements:• Degree of data accuracy needed• Security issues• Need for audit trails• The system’s ability to expand if the company needs to

grow or handle more data.