Requirements Prototyping

• Prototyping is used in both requirements phase and the design phase to :– demonstrate a concept

– demonstrate options • interface

• technology

• etc.

– demonstrate feasibility to reduce risks

• In Requirements phase prototyping may be used for:– requirements elicitation : especially in the UI area

– requirements validation : performance or functional completeness and consistency

Prototyping Process

• Establish the Prototyping Objectives – do not try to do too much and escalate cost and time

– consider some non-obvious usage of prototype• early training

• early test plan

• early documentation

• initial version for iterative development

• Define Prototype Functionality• Develop the Prototype• Evaluate the Prototype• Document the results from the Prototype

Two Major Prototyping Approaches

• Prototype that’s kept (Evolutionary)– no clear or formal requirements specification

– system is built and modified in piecemeal form and kept

– the final delivery is the solution system itself

• Prototype that is a Throw Away– detailed requirements specification is written as the

prototyping results come in, analyzed, and validated

– the final delivery is the requirements specification

• Evolutionary is very popular when there is new technology, especially with UI. (e.g. Web applications)

Evolutionary Prototyping

Build Prototype

“Minimal”Specification

Try out thePrototype

Is thePrototypeadequate ?

Deliver theSolution

YES

NO

Note : that there may not be any Final Specification ; but there is a lot of user interactionto perform usage verification andvalidation.

Pros and Cons of Evolutionary Prototyping• Advantages

– delivery speed (when everything goes well because the skipping of the formal specifications and reviews are removed)

– heavy user involvement throughout the development of the solution (increments of prototype are utilized -or “tested”- as soon as they are implemented)

• Disadvantages– Not suited for large, complex projects where documentation is

needed, more formal reviews are needed, and tighter management control is needed (when something goes wrong, there are not enough information for management to deal with).

– Continual modifications and changes, which may be unspecified, in the prototype make maintenance by others (even original authors) extremely difficult

– High possibility of scope creep which can cause increase in cost and time, forcing most of the work performed be charged under “time and material” basis. (This makes “fixed bid” a dangerous route.)

Move Towards Incremental Development Process

Define MajorRequirements

Deliver theSolution

Develop a HighLevel Design

Specify anIncrement

Develop anIncrement

Use theIncrement

IncrementAdequate ?

IntegrateIncrements

System& IncrementAdequate ?

Use theIncrement as Part of System

NO

Yes

No

Yes

* The key here is that there is an architecture or high level design to provide a general structure.

Throw-Away Prototyping

RequirementsOutline

Develop Prototype

Evaluate Prototype

RequirementsSpecification

If more clarification needed

Feeds into Design

Throw-Away Prototype

• Main purpose is to clarify requirements• Advantages:– provides an early check, clarification, and validation

of requirements

– provide an early assessment of risks

– non-code form (e.g. UI) may be quick and cheap

• Disadvantages:– the prototype many not have many reusable code

– may be pressured to keep and deliver the prototype code (e.g. technology prototype may not be user friendly or the code written is not easily maintainable))

Tools for Rapid Prototyping

• Visual Program Development – Visual Java, Visual Basic, Visual C++ which allows

• screen display UI and

• processing function prototyping

• Special Functional and Logic : Lisp and Prolog

• Database Centered Application Development– Progress and Forte class of 4GL development

environment• some relational database

• reports, query, etc. processing

– Database vendor development environment• Oracle application development (e.g. Oracle Forms, Oracle 9i)

• Web Based Application Development– Active Server Page, Java Server Page, WebSphere, etc.

Reusing Components in Prototypes

• Integrating a complete application into the prototype– a spreadsheet or a word processor application

– a database such as Access or SQL

– a complete legacy application

• Integrating individual components within some standard framework – JavaBeans or MS DCOMs (e.g. read mail, save text,

etc.)

– CORBA based application components