Transcript Dynamic Systems Development Method

44222: Information Systems Development
Dynamic Systems Development Method
Ian Perry
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E-mail:
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[email protected]
http://itsy.co.uk/ac/0506/Sem1/44222_ISD/
Traditional Systems Development
 Systems Development Life Cycle
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(Anderson R G, 1989)
Define Development Strategy
Systems Analysis
Systems Design
Systems Development
System and User Documentation
System Implementation
System Testing
System Maintenance
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44222: Information Systems Development: DSDM
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Structured Systems-Development
Budget
and
Schedule
User
Requirements
Feasibility
Study
Feasibility
Document
Analyze
the
System
New
System
Requirements
Document
User
Requirements
Design
the
System
Information Systems
in Business
Hardw are
Requirements
Hardw are
Conf iguration
Data
Sof tw are
Test Plan
Hardware
Evaluation
Hardw are
Build
the
System
New
System
System-Design
Document
Conversion
Operational
System
Hicks J
West Publishing 1990
Maintained
System
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44222: Information Systems Development: DSDM
Audit and
Maintenance
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‘Classic’ SSADM
Structured Systems Analysis & Design Method
4
Logical
Data Design
1
Analysis
2
Specification
Of Requirements
3
Selection of
Technical Options
6
Physical
Design
Requirements
Specification
Systems
Design
Specification
5
Logical
Process Design
Feasibility
Study Report
Information Systems in Business
Harry M
Pitman Publishing 1994.
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44222: Information Systems Development: DSDM
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Problems with these Approaches?
 Nothing!
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If you have a well defined problem that can be
solved by a sequential process with a fixed
number of separate stages.
 But!
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What if the Users are not exactly sure of what
they want the system to do?
What if the Implementors mis-interpret what
the Users have asked for?
What if the system needs to be delivered within
a short timescale?
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44222: Information Systems Development: DSDM
Slide 5
Dynamic Systems Development Method
http://www.dsdm.org/
 What is DSDM?
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The Dynamic Systems Development Method
(DSDM) is a framework of controls for the
development of Computer-based systems
It is independent of any particular set of tools
and techniques.
It can be applied to Information Systems
Development projects of any size.
Is especially good for Information Systems
Development projects with very short deadlines.
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44222: Information Systems Development: DSDM
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DSDM - Continued
 The lifecycle which DSDM uses is BOTH ‘iterative’
and ‘incremental’.
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A move away from traditional systems development is
essential if IT solution providers are to deliver
working systems in the ever decreasing timescales
demanded by businesses today.
 Even within a traditional systems development
environment, advantage can be gained from using
components of the DSDM approach:
 to ensure the right requirements are addressed.
 to reduce the time to delivery.
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44222: Information Systems Development: DSDM
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When to use DSDM?
 The application should have its functionality reasonably
visible through the user interface (screens, reports,
etc.):
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to enable prototyping to be used to maximum benefit.
 The project should be able to identify all of those who
will use the end result:
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these "Ambassador users" should participate throughout
the life of the project providing a two-way communication
channel between the business community and the IT
community.
 If the system is large, it should be able to be broken
down into smaller components:
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either for incremental delivery or for development by
parallel teams.
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44222: Information Systems Development: DSDM
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DSDM Principles - A Summary
 Active user involvement is imperative.
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DSDM teams must be empowered to make decisions.
 The focus is on frequent delivery of products.
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Fitness for business purpose is the essential criterion
for acceptance of deliverables.
 Iterative and incremental development is necessary
to converge on an accurate business solution.
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All changes during development are reversible.
 A collaborative and co-operative approach between
all stakeholders is essential.
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Testing is integrated throughout the life-cycle.
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44222: Information Systems Development: DSDM
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The ‘five’ Phases of DSDM
 DSDM provides a generic process which must
be tailored for use in a particular
organisation dependent on the business and
technical constraints.
 DSDM outlines a five phase process:
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feasibility study
business study
functional model iteration
design & build iteration
implementation
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44222: Information Systems Development: DSDM
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Feasibility Study
 To assess the suitability of the
application for a Rapid Application
Development (RAD) approach.
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To check that certain technical and
managerial conditions are likely to be met.
 The feasibility study typically lasts a
matter of weeks (rather than months).
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44222: Information Systems Development: DSDM
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Business Study
 To ‘scope’ the overall activity of the project
and provide a sound business and technical
basis for all future work.
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the high-level functional and non-functional
requirements are baselined.
a high-level model of the business functionality
and information requirements is produced.
the system architecture is outlined.
and the maintainability objectives are agreed.
 Like the feasibility study, the business study
is a short phase, of no more than a month.
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44222: Information Systems Development: DSDM
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Functional Model Iteration
 Prototyping to elicit requirements through
demonstration and feedback.
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Prototypes are built incrementally towards the tested
system which is placed in the user environment during
the implementation phase.
All prototypes in DSDM are intended to evolve into
the final system and are therefore built to be robust
enough for operational use & to satisfy any relevant
non-functional requirements, such as performance.
The completed functional model will consist of all
necessary high level analysis models and
documentation supported by functional prototypes
addressing detailed process & usability.
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44222: Information Systems Development: DSDM
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Design & Build Iteration
 Ensuring that prototypes are sufficiently well
engineered for use an operational environment.
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The dividing line between Functional Model and Design
& Build is not clear cut.
Some components of a system may well pass from the
Functional Model Iteration to the Design & Build
Iteration while other components are still very
sketchy or even non-existent.
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i.e. Design & Build activities may happen concurrently
with the Functional Model activities.
Similarly, in very large DSDM projects, the actual
implementation may be phased, so Design & Build may
be concurrent with some of the Implementation.
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44222: Information Systems Development: DSDM
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Implementation
 Put the latest increment into the operational environment,
train the users, and review what has been achieved.
 4 four possible outcomes:
 Everything delivered; no need for further development.
 New functional area discovered during development;
development returns to the Business Study phase and the
whole process is worked through.
 A less essential part of the functionality was missed out
due to time constraints; development returns to the start
of the Functional Model Iteration and adds the
functionality to the delivered system.
 A non-functional requirement was not satisfied as it well
as it would have been, given more time; development
returns to the Design & Build Iteration to rectify this.
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44222: Information Systems Development: DSDM
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The DSDM Lifecycle
Feasibility Study
• RAD approach suitable?
Business Study
• High level Requirements
Functional Model Iteration
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Agree Plan
Identify Functional Prototype
Create Functional Prototype
Review Prototype
Implementation
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Implement
Train Users
User Approval
Review Business
Design & Build Iteration
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Ian Perry
Agree Plan
Identify Design Prototypes
Create Design Prototypes
Review Design Prototypes
44222: Information Systems Development: DSDM
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How is DSDM Different?
 Traditional approaches:
 fix requirements, BUT allow time and resources to
vary during development.
 For DSDM;
 time is fixed, resources are fixed as far as possible,
BUT requirements are allowed to change.
 A very important product of the Business Study is:
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a clear prioritisation of the high-level functional and
non-functional requirements.
 DSDM projects guarantee to satisfy at least a
minimum subset of these requirements.
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44222: Information Systems Development: DSDM
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DSDM & the HCHE Project
 Time & Resources are fixed:
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Deadlines & Teams.
 Requirements might change:
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Read the ‘HCHE’ Case Study carefully.
Use the Interviews with “ambassador users” to
confirm requirements.
 DSDM matched to ISD Assignments:
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Business Study = Problem Statement
Functional Model = Prototype Documentation
Design & Build
= Prototype (for use in documentation)
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44222: Information Systems Development: DSDM
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