What is prototyping

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What is prototyping?

• Some traditional features
• An iterative process emphasizing
• Rapid development,
• Evaluative use,
• Feedback, and
• Modification
• Learning (based on feedback)
• Consideration of alternatives
• Concreteness (a real system is developed and
  presented to real users)

2
Uses of prototypes

• Principal use is to help customers and developers
  better understand system requirements.
• Experimentation stimulates anticipation of how a
  system could be used.
• Attempting to use functions together to
  accomplish some task can easily reveal
  requirements problems.

3
Prototyping benefits

• Misunderstandings exposed.
• Difficulttouse or confusing services identified
• Missing services detected
• Incomplete and/or inconsistent requirements found
  by analysts as prototype is being developed.
• Can demo feasibility and usefulness
• Basis for writing a system specification

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Prototyping process
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Prototyping in the software process

• Evolutionary prototyping (exploratory
  development in Chap. 3) prototype is produced
  and refined through a number of stages to become
  the final system.
• Throw-away prototyping prototype is produced to
  help elucidate / validate require-ments and then
  discarded. The system is then developed using
  some other development process.

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Approaches to prototyping
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Evolutionary prototyping
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Advantages of evolutionary prototyping over
normal system development

• Accelerated delivery quick availability is
  sometimes more important than details of
  functionality or maintainability.
• User engagement system is more likely to meet
  user requirements and users are more likely to
  want to make it work.

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Evolutionary prototyping problems

• Management problems
• Poor fit with existing waterfall management model
• Specialized developer skills required
• Maintenance problems continual change tends to
  corrupt system structure so long-term maintenance
  is expensive.
• Contractual problems no system require-ments
  specification to serve as basis for contract

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Incremental development process
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Throw-away prototyping

• Used to reduce requirements risk.
• Initial prototype is developed from outline
  requirements, delivered for experiment, and
  modified until risk is acceptably low.

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Throw-away prototyping
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Throw-away prototype delivery

• Developers may be pressurized to deliver a
  throw-away prototype as the final system.
• This is very problematic...
• It may be impossible to meet non-functional
  requirements.
• The prototype is almost certainly undocumented.
• The system may be poorly structured and therefore
  difficult to maintain.
• Normal quality standards may not have been
  applied.

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No, no, no! I wont deliver the prototype to you!
User Mgmt
Developer
Air Tank
Pressurizing the Developer
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Implementation techniques

• Various techniques may be used for rapid
  development
• Dynamic high-level language development
• Database programming (4GLs)
• Component and application assembly
• These are not mutually exclusive they are often
  used together.
• Visual programming is an inherent part of most
  prototype development systems.

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Dynamic high-level languages

• Include powerful data management facilities
  often typeless and interpretive
• Require large run-time support system not
  normally used for large system development.
• Some offer excellent GUI development facilities.
• Some have an integrated support environment whose
  facilities may be used in the prototype.
• Examples Lisp (list structure based), Prolog
  (logic based), and Smalltalk (object-oriented)

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Choice of prototyping language

• What is the application domain? (e.g., NLP?,
  matrix manipulation?)
• What user interaction is required? (text-based?
  Web-based?)
• What support environment comes with the language?
  (e.g., tools, components)

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Choice of prototyping language

• What support environment comes with the language?
  (e.g., tools, components)
• Different parts of the system may be programmed
  in different languages. However, there may be
  problems with language communications.
• A multi-paradigm language (e.g., LOOPS) can
  reduce this problem.

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Database programming 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

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Database programming languages

• The language environment is some-times known as
  a fourth-generation language (4GL)
• Cost-effective for small to medium sized business
  systems
• Examples include Informix, Appgen, Sculptor, and
  Power-4GL.

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Application linking in compound documents
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Visual programming

• Scripting languages such as Visual Basic support
  visual programming where the prototype is
  developed by creating a user interface from
  standard items and associating components with
  these items.
• A large library of components exists to support
  this type of development
• These may be tailored to suit the specific
  application requirements.

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Visual programming with reuse
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Problems with visual development

• Difficult to coordinate team-based development
• No explicit system architecture (hidden)
• Complex dependencies between parts of the program
  can cause maintainability problems.