CMSC 345

Prototyping

Prototyping the Requirements Investigate requirements

Customer uncertainty Are requirements realistic

Risk Reduction Reduces number of problems with

requirements and overall development cost

Benefits of Prototyping Identify misunderstandings between

developers and users Detect missing user services Identify and refine hard-to-use or confusing

user services Identify incomplete or inconsistent

requirements A working (but incomplete) system is quickly

available to demo feasibility and usefulness Basis for specification for production quality

system

Approaches to Prototyping Evolutionary Prototyping

Give the user an incomplete system, then modify and augment as the requirements become clear

Throw-Away Prototyping Help with requirements analysis and

validation then discarded

Evolutionary Prototyping Objective: to deliver a working system

to the end-users Starts with limited understanding of

requirements System is changed and augmented as

new requirements are discovered Incorporate well understood

requirements, then move on to those which are unclear

May never be a system specification

Problems withEvolutionary Prototyping SW Management set up to deal

with regular deliverables to asses progress. Prototypes evolve quickly. No docs.

Continual change corrupts the structure of the prototype, making maintenance difficult and costly

Requires small teams of highly skilled and motivated individuals

Throw-Away Prototyping Objective: Validate or derive the

system requirements Priority is to understand

requirements that are unclear Extends requirements analysis

with intention of reducing life cycle costs

Problems withThrow-Away Prototyping Important features may be left out

of prototype to simplify rapid development

Nonfunctional requirements such as those concerning reliability, robustness and safety cannot be adequately tested in prototype

Incremental Development Combines advantages of evolutionary

prototyping with control required for large-scale development

Avoids problem of constant change More manageable since normal

software process standards are followed Problem – software architecture must

be established before requirements are complete so requirements tend to be constrained by the architecture.

GUI Prototyping Developers cannot impose their

view on the user. User must take part.

Use evolutionary Prototyping Initial interface produced, evaluated

by users and revised until users satisfied

May be re-implemented

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July 1998

1998 2025

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