Transcript A Prototyping Lifecycle

A Prototyping Lifecycle
The Waterefall Model and
Prototyping
 As early as the 1980’s the classic “Waterfall
model” of software development was criticised
– as a “fake”
– as failing to address the fundamental issue of the
software crisis
• incomplete, inaccurate, changed requirements
– for pushing user evaluation to the end of the lifecycle
 A “prototyping” RAD lifecycle proposed instead
– rejected as “unmanageable”
– prototyping restricted to requirements gathering
 RAD has re-emerged in the last two years
DSDM2- a RAD Process
 The Dynamic Systems Development Method
(DSDM2) is a public domain standard
specification for a Rapid Application
Development (RAD) or evolutionary delivery
process
– supported by more than 200 companies in the UK
– worthy as an example of a modern, industrial strength,
lifecycle for prototyping
DSDM Overview
 “Three pizzas and a cheese”: the five phases
of DSDM are:
1. Feasibility study
2. Business study
3. Functional model iteration
4. System design and build iteration
5. Implementation
“Three Pizzas and a Cheese”
DSDM Feasibility Study
 An assessment of whether or not DSDM is
appropriate to the project.
– Has serious impact on user community; worth it in
trade-off to deliver in sharp time-scales?
– Feasibility study should be short, sharp
– Deliverables include Feasibility Report; Outline
Development Plan and a fast prototype
DSDM Business Study
 Aim is to gain understanding of the business
processes of the client organisation
 The activity is strongly collaborative
– involves facilitated workshops
 First deliverable is a Business Area Definition
– high-level, prioritised, view of processes to be
automated
– identifies business processes, user classes, user
representatives for development
 Other deliverables are System Architecture Definition and
Outline Prototyping Plan
DSDM Functional Model
Iteration
 Shares with the Design and Build Iteration the
following cycles of four activities:
1. Identify what you are doing in the cycle
2. Agree how you will go about doing it
3. Do it
4. Check that you did it right
• by reviewing documents, demonstrating a prototype or
software testing
 Delivers Analysis model(s) and major software
components
DSDM Functional Iteration
(contin.)
 Other products include
– Prioritised functions
• core functions are guaranteed delivery
– Functional prototyping review documents
• maintains history of user feedback
– Non-functional requirements
– Risk analysis of future development
DSDM Design and Build
Iteration
 Product is the Tested System
– tests are iterative
– tested system will not necessarily deliver ALL
requirements, but will deliver the core “minimum
usable subset”)
– early deliverables are design prototypes and design
prototyping review documents.
DSDM Implementation
 Covers cutover from development
environment to operational environment
 Products include
–
–
–
–
delivered system and documentation
User Manual
trained user population
Project Review Document
Principles of DSDM
 Active user involvement is imperative
 DSDM teams must be empowered to make
decisions
 Focus is on frequent delivery of products
 Fitness for purpose is the essential criterion for
acceptance of deliverables
 Iterative and incremental development is
necessary to converge on an accurate business
solution
 All changes during development are reversible
Principles of DSDM (contin.)
 Requirements are base-lined at a high level
 Testing is integrated throughout the lifecycle
 A collaborative and co-operative approach
between all stakeholders is essential