Transcript Slide 1

3.3.1
• Types of specification:
– Requirements specification
– Design specification
– System specification
and the differences between them.
• 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.
• It should contain:
• What the users what the system to be able to do.
• http://en.wikipedia.org/wiki/Functional_requirements
• How the user wants the system to behave.
• http://en.wikipedia.org/wiki/Non-functional_requirements
• 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.
• 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.
• 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?
• 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
• The contents should include:
– Processing requirements/queries
– Data structures
– Modelling diagrams
• DFDs, ERDs, STDs
– Hardware
– Software/programming language to
be used
– Test plan
• 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.
• This specification defines the requirements of the system
including:
– General system requirements:
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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.