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Prototyping Strategies

Prototyping Strategies. Overview. Prototyping is a well understood and used technique in engineering where novel products are tested by testing a model prototype prototypes can be “throw away” (e.g., scale models) or go into commercial use (Concorde!) In software development prototypes can be

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Prototyping Strategies

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  1. Prototyping Strategies

  2. Overview • Prototyping is a well understood and used technique in engineering where novel products are tested by testing a model prototype • prototypes can be “throw away” (e.g., scale models) or go into commercial use (Concorde!) • In software development prototypes can be • paper-based • software-based

  3. Aims of Prototyping in Software The aim of prototyping is to resolve uncertainty about • functional requirements • operation sequences • user support needs • required representations • “Look and Feel” of the interface

  4. Prototyping Techniques The three major kinds of prototyping are • “Throw away” prototyping (a.k.a. “rapid prototyping”) • used exclusively in requirements gathering • Incremental prototyping • not actually prototyping at all, but the delivery of prioritised functions incrementally to a single, overall design • Evolutionary prototyping (a.k.a “Rapid Application Development, RAD) • as for incremental prototyping but with evolving design

  5. Other (Lesser) Kinds of Prototyping • Full prototype • full functionality, lower performance than production software • Horizontal prototype • displays “breadth” of functionality, no “back end” support • Vertical prototype • full functionality and performance of a “slice” of a system • High Fidelity prototyping • prototyping through alternative media, e.g. video

  6. Other (Lesser) Kinds of Prototyping (continued) • Low fidelity prototyping • lesser, cheaper materials • Chauffeured prototyping • user observed “driving” the system • Wizard of Oz prototyping • as chauffeured, but with the observer unobserved! • Requirements Animation

  7. Paper-based Prototyping Paper-based prototyping is useful only for “throw away” schemes (obviously!). Can include • Holistic Design • role-playing; e,g., CRC cards in OO development • Sketching and Metaphor • visual brainstorming, screen design, icons etc.,

  8. Paper-based Prototyping (continued) • Scenarios • e.g. Use Cases in OO development • Storyboards and Snapshots • using “film-scripting” techniques to visualise interactions between users and the system

  9. Software Prototypes A software prototype • is “executable” • will not have a generalised lifetime • can be thrown away, or evolve • may serve many different purposes • should be “quick and dirty” (and cheap!) • is an integral part of user-centred design approaches based on evaluation/modification

  10. Software prototyping tools • Facades and Requirements Animators • e.g., Demo II • interfaces demonstrated through “slide shows” • useful only for throw away prototyping • Screen generators • e.g., Protogen • GUIs built rapidly by “screen-painting” then hooked into application code • RAD tools • e.g., Visual Basic, Delphi • can be used for building full apps.

  11. RAD tools • Rapid Application Development (RAD) tools are being used generically for prototyping • i.e., even when only facading is required • Can lead to confusion about what kind of prototype is being built • heightened, unrealistic user expectations • lower Quality Assurance • It is therefore important to be able to evaluate tools, and establish a proper prototyping process

  12. Visual Basic and Delphi • VB (Microsoft) and Delphi (Borland) are both RAD tools for MS-Windows applications • Both enable user to “paint” screens by drag-and-drop operations on predefined GUI elements (widgets) • scrollbars, menus, buttons, list boxes, dialo boxes etc. • Both allow user-customisation of widget properties • colour, size, text, formatting etc.

  13. Event-driven Programming • VB and Delphi give close support to event-driven programming • where app. is idle until its behaviour is triggered by a user-initiated “event” • Each predefined widget has a skeleton body of methods (procedures) to support events • e.g., LeftMouseButtonDown( ) • user supplies implementation code • Screens can be animated prior to coding specific application behaviour

  14. Event-Driven Programming (contin.) Development procedure is essentially 1. Paint the screen with widgets (actually called Controls) 2. Customise their attributes via a Properties Form 3. Supply implementations of their event procedures write code “on back” of Controls 4. Write “back-end” code in separate modules

  15. Visual Basic versus Delphi • Both support “reusable” Controls • VB is “object-based” • reuse of “back-end” code is difficult • VB code is a form of BASIC - a pre-”structured” language • encourages hardwiring of Controls to event code • VB is an interpreted environment • 25x slower than a fully compiled environment

  16. Visual Basic versus Delphi • Delphi is object-oriented • “back-end” objects can be resused and customised via inheritance (an OO feature) • Delphi code is Object Pascal • fully-fledged OO language also used in the Macintosh Apple’s operating system • Delphi code is compiled • faster

  17. Implications • VB is good for • “throw away” prototyping, facading, requirements animation • screen generation • can be hooked into C++ or J++ code • Delphi is good for • incremental prototyping • RAD

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