44222: information systems development dynamic systems development method ian perry room:c49...

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


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


‘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.


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?


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.


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.


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.


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.


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


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).


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.


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.


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.


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.


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?


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.


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)

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