4.2 Activities

• Reading, Review, and Inspection
  • A reasonable process for evolving from definition to specification is repeated review for validity, consistency, completeness, and realism.

• Prototyping
  • Especially useful for validity and completeness

• Static model checking
  • Requires a more formal notation and supporting tools

4.2.1 Prototyping

• The principal use is to help customers and developers understand the requirements for the system
• The prototype may be used for user training before a final system is delivered
• The prototype may be used for back-to-back testing

4.2.1.0 Prototyping benefits  

• Misunderstandings between software users and developers are exposed
• Missing services may be detected
• Confusing services may be identified
• A working system is available early in the process
• The prototype may serve as a basis for deriving a system specification

4.2.1.0 Approaches  

• Evolutionary prototyping
• Throw-away prototyping

4.2.1.0 Evolutionary prototyping  

• Must be used for systems where the specification cannot be developed in advance e.g. AI systems and user interface systems
• Based on techniques which allow rapid system iterations
• Verification is impossible as there is no specification. Validation means demonstrating the adequacy of the system

4.2.1.0 Throw-away prototyping  

• Used to reduce requirements risk
• The prototype is developed from an initial specification, delivered for experiment then discarded
• The throw-away prototype should NOT be considered as a final system
  • Some system characteristics may have been left out
  • There is no specification for long-term maintenance
  • The system will be poorly structured and difficult to maintain

4.2.1.0 Prototyping techniques  

• Executable specification languages
• Very high-level languages
• Application generators and 4GLs
• Composition of reusable components

4.2.1.0 Very high-level languages  

• Languages which include powerful data management facilities
• Need a large run-time support system. Not normally used for large system development
• Some languages offer excellent UI development facilities
• Some languages have an integrated support environment whose facilities may be used in the prototype

4.2.1.0 Prototyping languages  

Commonly used are

• SmallTalk
• LISP
• Prolog
• 4GLs

4.2.1.0 Fourth-generation languages  

• Domain specific languages for business systems based around a database management system
• Normally include a database query language, a screen generator, a report generator and a spreadsheet
• May be integrated with a CASE toolset
• Cost-effective for small to medium sized business systems 4GLs

4.2.1.0 User interface prototyping  

• It is impossible to pre-specify the look and feel of a user interface in an effective way. prototyping is essential
• UI development consumes an increasing part of overall system development costs
• Prototyping may use very high loevel languages such as Smalltalk or Lisp
• User interface generators may be used to "draw" the interface and simulate its functionality