Prototyping

1
Prototyping
2
Scenario

• Customer We would like the word processor to
  check the spelling of what is typed in. We also
  need the checking to take place very quickly.
• Developer OK. What sort of features do you
  want? I mean, aprt from speed, how would you
  like the system to perform the spell check?
• Customer Oh! Were not really sure. All wed
  need is for the computer to make sure that our
  text is spelled correctly. But, could the
  computer ask us for the correct spelling if it
  came across a word that it didnt know about?
• Developer Yes, thats possible.
• Customer and what if we wanted the computer
  to skip certain words?
• Developer What kind of word?
• Customer Words that we told it to ignore.
• Developer Yes, I see. I think that would be
  possible too.
• Customer How would the system know that words
  are spelled correctly?
• Developer The best way to do this, would be for
  the system to have a dictionary of known words,
  and the system would check your text against
  these words.
• Customer Im having difficulty visualizing how
  that would work for us. Would it be possible for
  us to see how this would work on the computer?
• Developer Yes. I could build a prototype to
  show you how this would work. You could use the
  prototype and see if it is actually what you
  needed. It will also help me to better understand
  your needs as well.

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What is a prototype?

• Anything that approximates any aspect of your
  final product!
• Why prototype?
• To gain a better understanding of a problem.
• Will the proposed approach work? Resolve
  unknowns.
• To give the client a feel for what the final
  product will do/look like.
• This may assist in clarifying requirements.
• Communication
• Management, customers, vendors, financiers,
• Integration
• Will all the pieces/components fit?
• Milestones
• Is the project of schedule?
• Detect problems/incompatibilities.

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Types of prototype

• Experimental
• Focused on specific aspects of the project.
• Alpha
• Almost complete system given to trusted and
  valued clients with the aim of identifying bugs
  and areas of improvement.
• Beta
• Complete system. Last chance to find bugs before
  final production.
• Preproduction
• Pilot production system. Incorporates all changes
  from previous prototypes.

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Planned vs unplanned

• Planned prototyping
• Reduces risk
• May reduce time to market
• May reduce cost
• Unplanned prototyping
• Increased time to market
• Increased cost

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Step-by-step

• Define the purpose(s) of the prototype.
• Establish what is to be done as part of the
  prototype (and what is not).
• Determine the form of the prototype.
• Set design plan and establish cost.
• Define tests to be conducted and data to be
  collected,

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Pitfalls

• Prototype doesnt contribute to project goals.
• Prototype delays time to market.
• Schedule is too tight to integrate the results of
  the prototype.
• Excessive cost.

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Prototype process model

• Similar to other types of software development,
  the prototyping process should follow a defined
  software process model.
• Analyze requirements
• The developer needs to understand the content and
  nature of the customers initial requirements.
• Determine the functionality to be represented in
  the prototype.
• Prototype design
• Chose a suitable implementation approach for the
  prototype.
• The prototype design should be baseded on the
  results of the analysis of the requirements and
  the choice of implementation.
• Prototype construction
• Actually code the prototype
• Evaluation
• Evaluate the prototype and incorporate new
  knowledge into the product requirements and
  design.

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Analyze requirements

• The functionality of the prototype should focus
  on the requirements that are unclear or fuzzy.
• Decide on the kind of prototype
• Throwaway prototyping supports the rapid
  development of a trail version of the functional
  behavior for demonstration purposes. Aims to
  clarify requirements knowing that additional
  requirements are likely to be uncovered.
• Evolutionary prototyping requirements are well
  understood but there is a need to make sure that
  the implementation strategy is appropriate. The
  prototype may find its way into the final
  product.
• It is important to keep the client informed about
  the nature of the prototype.
• Limited functionality does not posses full set
  of features or performance characteristics of the
  final version.

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Spell check (again)

• In the spell check example, we build a throwaway
  prototype to concentrate on the skipping of
  words.
• Requirements of the prototype
• The word processing system should possess a means
  of checking the spelling of inputted text and
  reporting incorrectly spelled words.
• The system should provide a means of changing
  incorrectly spelled words.
• The system should possess a dictionary of
  correctly spelled words against which the input
  text is compared.
• The dictionary should be expandable so that users
  can add new words.
• During the spell check process, the user should
  be able to ignore the spelling of any word
  regardless of whether it is spelled correctly or
  not.
• Assumptions about the requirements should be
  recorded and presented to the client during
  prototype evaluation.

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Prototype design

• To construct a prototype, a suitable
  implementation approach must be used.
• The approach must offer features that satisfy the
  general requirements of prototyping rapidity and
  ease of modification.
• An approach that relies on an overly complex and
  lengthy development cycle is obviously
  unsuitable.
• During the design of a throwaway prototype,
  performance is not a critical factor, so
  efficiency of design is not a priority.
• Since the prototype will be discarded after use
• Maintainability or elegance of the design is not
  an important consideration.
• Large amount of documentation is also not
  required.
• Keep functionality to a minimum focus on the
  unclear or fuzzy requirements.

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Prototype construction

• During the design of the spell check prototype,
  three tasks were performed
• User interface construction
• Implementation of functional behavior
• Development of the data model.

Developer
Customer
User Interface
Functional Behavior
Data Model
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Prototype construction

• The aim of the prototype is to provide a working
  system in the least possible time.
• For the spell check example, design decisions to
  achieve this goal include
• Not to include any test entry facilities use
  existing tools for this purpose. Our focus is on
  the spell checking subsystem.
• Text-based output facilities. The correctly
  spelled output is saved to a file for validation
  purposes.
• Display the current state of the spell checking
  process feedback information for both the
  developer and the client. A separate display
  panel might be used to do this, even though it
  might not be part of the final product.

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Prototype construction data model

• In terms of the data model, the prototype is no
  difference from any other piece of software in
  that it requires information in some form to
  process.
• Storage in memory, or on disk?
• How used?
• What needs to be modeled?
• Volatility/persistence of the data?
• Spell check prototype
• Words read in from and written to a separate
  file. Therefore we need to read words into
  memory. An array of words is sufficient for the
  purposes of the prototype.
• Where to store checked words. For the prototype,
  we dicide to simply write them to an output file
  for verification later.
• The dictionary. The correctly spelled words is
  persistent and therefore stored in a disk file.
  They need to be stored in memory as the program
  runs, so we elect to keep them in an array.

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User evaluation

• Once the prototype is complete, interested
  parties should use it and provide feedback to the
  developer.
• Developer The ignore word function simply skips
  the current word which is incorrect.
• Customer yes but what if the same word crops
  up again and again? I will have to keep skipping
  each occurrence with the ignore word button each
  time, wont I?
• Developer Yes.
• Customer Could it be possible for me to skip
  all occurrences of that particular word in one
  go?
• Developer Do you mean an ignore all
  function?
• Customer Yes, something like that

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Evolution

• The additional requirements identified can be
  incorporated into the spell check prototype.
• The additional requirements are
• The need to ignore all occurrences of a
  particular word.
• To change the spelling of all the occurrences of
  a particular word.
• The need for separate dictionaries. E.g., this
  feature could be used to allow for different
  spelling of certain words to be checked for,
  I.e., difference between Australian and US
  spelling (colour vs color, specialise vs
  specialize, )