-. The benefits of developing a prototype early in the software process are :
	(1) Misunderstandings between software developers and users may be identified as the system functions 
                    are demonstrated.
	(2) Missing user services may be detected.
	(3) Difficult-to-use or confusing user services may be identified and refined.
	(4) Software development staff may find incomplete and/or inconsistent requirements as the prototype is
	   developed.
	(5) A working, albeit limited, system is available quickly to demonstrate the feasibility and usefulness of
                     the application to management.
	(6) The prototype serces as a basis for writing the specification for a production quality system.
   -. Software prototypes also have other uses:
	(1) User training
	(2) System testing
   -. The final stage of the process is prototype evaluation.
   -. There are non-technical managerial problems which may make it difficult to use prototyping in some organizations.

   8.1 Prototyping in the software process
       -. One way of tackling this difficulty is to use an evolutionary approach to systems development.
       -. Alternatively, a deliverate decision mignt be made to build a 'throw-away' prototype to help requirements analysis
        and validation.
       -. There is an important difference between the objectives of evolutionary and throw-away programming:
	(1) The objective of evolutionary prototyping is to deliver a working system to end-users.
	(2) The objective of throw-away prototyping is to validate or derive the system requirements.

       8.1.1 Evolutionary prototyping
	-. There are three main problems with evolutionary prototyping which are particularly important when large, 
	 long-lifetime systems are to be developed:
	-. Difficulties do not mean that evolutionary prototyping should be rejected.
       8.1.2 Throw-away prototyping
	-. This approach extends the requirements analysis process with the intention of reducing overall lige cycle costs.
	-. Customers and end-users should resist the temptation to turn the throw-away prototyping into a delivered system 
                   that is put into use.
       8.1.3 Incremental development
	-. This incremental development model involves developing the requirements and delivering the system in an 
	 incremental fashion.
	-. Incremental development is more manageable than evolutionary prototyping as the normal software process 
                   standards are followed.
	-. A problem with incremental development is that the system architecture has to be estabilished before the
	 requirements are complete.
	
   8.2 Prototyping techniques
       -. There are a number of techniques which have been used for system prototyping. These include:
       	+. Executable specification languages,
	+. very high level language,
	+. application generators and fourth-generation languages,	
	+. composition of reusable components.

       8.2.1 Executable specification languages
	-. There are practical difficulties in applying this approach.

       8.2.2 Very high level languages
	-. Very high level languages are programming languages which include powerful data management facilities.
	-. Very high level dynamic languages are not normally used for large system development because they
                   need a large run-time support system.

       8.2.3 Fourth-generation languages
	-. Fourth-generation languages are successful because there is a great deal of commonality across data
	 processing applications.
	-. There is no standardization or uniformity across fourth-generation languages.

       8.2.4 Composition of reusable components
	-. Prototyping with reusable components involves developing a system specification by taking account of
	 what reusable components are available.      
	-. Prototyping using reusable components is often combined with other approaches using very high level 
	 or fourth-generation languages.

   8.3 User interface prototyping
       -. Interface generation systems may be based aroun user interface management systems which provide basic user interface
        functionality such as menu selection, object display and so on.
       -. From a software engineering point of view, it is important to realize that user interface prototyping is an essential part 
        of the process.