44222: information systems development dynamic systems development method ian perry room:c49...
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44222: Information Systems Development
Dynamic Systems Development Method
Ian Perry Room: C49
Extension: 7287E-mail: [email protected]
http://itsy.co.uk/ac/0506/Sem1/44222_ISD/
Ian Perry 44222: Information Systems Development: DSDM Slide 2
Traditional Systems Development
Systems Development Life Cycle (Anderson R G, 1989)
Define Development Strategy Systems Analysis Systems Design Systems Development System and User Documentation System Implementation System Testing System Maintenance
Ian Perry 44222: Information Systems Development: DSDM Slide 3
Structured Systems-Development
UserRequirements
FeasibilityDocument
UserRequirements
HardwareConfiguration
DataNew
SystemRequirements
Document
HardwareRequirements
SoftwareTest Plan
System-DesignDocument
Hardware
NewSystem
SystemOperational
SystemMaintained
System
Budgetand
Schedule
Hicks J
West Publishing 1990
Information Systemsin Business
FeasibilityStudy
Maintenance
Analyzethe
SystemHardware
Design
Evaluation
the theSystem
BuildConversion
Audit and
Ian Perry 44222: Information Systems Development: DSDM Slide 4
‘Classic’ SSADMStructured Systems Analysis & Design Method
1Analysis
2Specification
Of Requirements
3Selection of
Technical Options
4Logical
Data Design
5Logical
Process Design
6PhysicalDesign
FeasibilityStudy Report
SystemsDesign
Specification
RequirementsSpecification
Information Systems in BusinessHarry MPitman Publishing 1994.
Ian Perry 44222: Information Systems Development: DSDM Slide 5
Problems with these Approaches?
Nothing! If you have a well defined problem that can
be solved by a sequential process with a fixed number of separate stages.
But! 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?
Ian Perry 44222: Information Systems Development: DSDM Slide 6
Dynamic Systems Development Method
http://www.dsdm.org/
What is DSDM? 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.
Ian Perry 44222: Information Systems Development: DSDM Slide 7
DSDM - Continued
The lifecycle which DSDM uses is BOTH ‘iterative’ and ‘incremental’.
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.
Ian Perry 44222: Information Systems Development: DSDM Slide 8
When to use DSDM?
The application should have its functionality reasonably visible through the user interface (screens, reports, etc.):
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: 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:
either for incremental delivery or for development by parallel teams.
Ian Perry 44222: Information Systems Development: DSDM Slide 9
DSDM Principles - A Summary
Active user involvement is imperative. DSDM teams must be empowered to make decisions.
The focus is on frequent delivery of products. 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. All changes during development are reversible.
A collaborative and co-operative approach between all stakeholders is essential.
Testing is integrated throughout the life-cycle.
Ian Perry 44222: Information Systems Development: DSDM Slide 10
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: feasibility study business study functional model iteration design & build iteration implementation
Ian Perry 44222: Information Systems Development: DSDM Slide 11
Feasibility Study
To assess the suitability of the application for a Rapid Application Development (RAD) approach. 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).
Ian Perry 44222: Information Systems Development: DSDM Slide 12
Business Study
To ‘scope’ the overall activity of the project and provide a sound business and technical basis for all future work. 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.
Ian Perry 44222: Information Systems Development: DSDM Slide 13
Functional Model Iteration
Prototyping to elicit requirements through demonstration and feedback.
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.
Ian Perry 44222: Information Systems Development: DSDM Slide 14
Design & Build Iteration
Ensuring that prototypes are sufficiently well engineered for use an operational environment.
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. 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.
Ian Perry 44222: Information Systems Development: DSDM Slide 15
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.
Ian Perry 44222: Information Systems Development: DSDM Slide 16
The DSDM Lifecycle
Functional Model Iteration• Agree Plan• Identify Functional Prototype• Create Functional Prototype• Review Prototype
Design & Build Iteration• Agree Plan• Identify Design Prototypes• Create Design Prototypes• Review Design Prototypes
Implementation• Implement• Train Users• User Approval• Review Business
Business Study• High level Requirements
Feasibility Study• RAD approach suitable?
Ian Perry 44222: Information Systems Development: DSDM Slide 17
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: 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.
Ian Perry 44222: Information Systems Development: DSDM Slide 18
DSDM & the HCHE Project
Time & Resources are fixed: Deadlines & Teams.
Requirements might change: Read the ‘HCHE’ Case Study carefully. Use the Interviews with “ambassador users” to
confirm requirements. DSDM matched to ISD Assignments:
Business Study = Problem Statement Functional Model = Prototype
Documentation Design & Build = Prototype (for use in
documentation)