Types of Requirements - created from Mind Map

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What are requirements ?

Behaviour or quality a new system is required to have

Behaviour requirements are usually called FUNCTIONAL

Quality requirements are usually called NON-FUNCTIONAL

Something a system must DO

Non-functional = how well the system must do something

How quickly, how easy to use, in what environment

Usability (System Quality for the user)

sub-class of non-functional, but so important they’re often listed separately

How easy, pleasant, error-free, stress-free the system is to use…

Users’ characteristics: screen must be accessible for visually-handicapped users

Tasks: interface must allow fast input of repetitious data without causing RSI(repetitive strain injury)

Situational factors: screens must be readable in low-light conditions

Functional (System Action)

What a system must do (description includes an active verb)

Will probably become programs or scripts in the final system

Initially documented by Use Case Diagrams

Can also be modelled with Data Flow Diagrams

Functional (Data) Requirements

Enrol a student on a module

Create a new customer order

Produce monthly sales report

Record all customer orders

Record all student enrolments

Modelled with Entity Relationship Diagram

Will become database in final system

Non-Functional (System Quality)

How, or how well the system performs

Response times

Volumes of data

Security issues

These will become measurable quality aspects of the final system

Why Specify Requirements?

Each system has unique requirements—need to be sure we get them right

Get this wrong, and we risk

Waste of money, time and resources

Disappointing users and sponsors

Lost business opportunities

Possible harm to people

Reasons to use Use Cases

Easy to understand

Easy to map onto business goals

Helps developers focus on building useful functionality

Helps divide a large project into smaller increments

Types of Requirements