3.2.4 Functional and non-functional requirements A.1 Functional requirements
Statements of services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations.
B.1 Examples of functional requirements
? The user shall 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 be allocated a unique identifier (ORDER_ID) which the user shall be able
to copy to the account’s permanent storage area.
A.2 Non-functional requirements
constraints on the services or functions offered by the system such as timing constraints, constraints on the development process, standards, etc.
B.1 Non-functional classifications C.1 Product requirements
Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc.
C.2 Organisational requirements
Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc.
C.3 External requirements
Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc.
B.2 Non-functional requirements examples C.1 Product requirement
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4.C.8 It shall be possible for all necessary communication between the APSE(Ada Programming Support Environment) and the user to be expressed in the standard Ada character set
C.2 Organisational requirement
9.3.2 The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP-STAN-95
C.3 External requirement
7.6.5 The system shall not disclose any personal information about customers apart from their name and reference number to the operators of the system
B.3 Requirements measures
Example: Experienced controllers shall be able to use all the system functions after a total of two hours training. After this training, the average number of errors made by experienced users shall not exceed two per day.
A.3 Domain requirements
Requirements that come from the application domain of the system and that reflect characteristics of that domain
B.1 examples C.1
Because of copyright restrictions, some documents must be deleted immediately on arrival. Depending on the user’s requirements, these documents will either be printed locally on the system server for manually forwarding to the user or routed to a network printer.
The deceleration of the train shall be computed as: Dtrain = Dcontrol + Dgradient where Dgradient is 9.81ms2 * compensated gradient/alpha and where the values of 9.81ms2 /alpha are known for different types of train.
C.2
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3.3 The requirements document
3.3.1 Concept
? The requirements document is the official statement of what is required of the system
developers.
? Should include both a definition of user requirements and a specification of the system
requirements.
? It is NOT a design document. As far as possible, it should set of WHAT the system should do
rather than HOW it should do it
3.3.2 Requirements document structure
1. 2. 3. 4. 5. 6. 7. 8. 9.
Introduction Glossary
User requirements definition System architecture
System requirements specification System models System evolution Appendices Index
3.3.3 Ways of writing a system requirements specification A.1 Natural language
The requirements are written using numbered sentences in natural language. Each sentence should express one requirement.
A.2 Structured natural language
The requirements are written in natural language on a standard form or template. Each field provides information about an aspect of the requirement.
B.1 Form-based specifications
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B.2 Tabular specification
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