ise-lecture2-methods_modelling.pptx

7/27/2019 ISE-Lecture2-Methods_Modelling.pptx

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Lecture 2: Methods

& ModelingInformation System Engineering

FGR Summer 1ISE-Lecture2-


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Outline

System development methodology



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Introduction

Purpose of the systems development functionis to develop effectivesystems in the mostefficientway possible.

The traditional systems development lifecycle SDLC- (with which you are allfamiliar) was a first attempt to provide acontrolled environment for systemsdevelopment



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Systems development life cycle



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SDLC

Main criticisms: rigid, no back-tracking oriterations allowed

Modern dev. frameworks built from this.



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systems development methodology


Genericdevelopment

framework

Essential Steps Optional Steps

Order of steps TOOLS &TECHNIQUES

METHODOLOGY


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niques

Defining a Methodology

FGR SummerISE-Lecture2- 7

Avison & Fitzgerald (2006)


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Method


Technical Model


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Tools & Techniques

The Technical model


DATAMODEL

PROCESSMODEL

BEHAVIORMODEL


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Managerial model

Order in which steps are to be covered, how tocontrol the activities.

It provides the frameworkwithin which

the development will take place. It defines stages, stepsand tasksto

be undertaken.



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Managerial model


WHEN WHICH HOW

END - DELIVERABLES


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End-deliverables (1)

Each defined stage will have aprescribed end-deliverable or productwhich must be delivered as the stage

is completed. Similarly, each step or task may have

a sub-deliverable or sub-product

associated with it



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End-deliverables (2)

End-deliverable may be presented inthe form of a

document/specification, a

design, a presentationor asgenerated, tested code. It provides aprescribed review stage and milestone

for the project. Forms an essential part of project

management and review process.



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The modelling concept

Model:a simplification/abstraction of thereal object from a particular

perspective

view of a particular part of a system(often a graphical representation)providing clear and unambiguousinformation about the system



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Model: An example 2D model of ahouse



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Model: An example 3D model of ahouse



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Different real world models

Road map: model of a transport networkwithin a particular area.

Architects blueprint: schematicrepresentation of a building or a bridge.

A musical score: a graphical/textrepresentation of the musical notes andtempo required to play a piece of music



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Software models:Example Class diagram



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Software models: Example Sequencediagram



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Software models: Example Story boardTo set out the

sequence for ananimation or websitedesign



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Software models: Example Use casediagram

To show theinteraction

between userand system



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Software models: Example Gantt chart

To depict the time availableand the scheduling withinthat time



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Importance of models

Modelling tools enable analyst to:

Focusupon key systems features anddivorce them from any physical implementation

issues.

Investigatesystem requirements withlow cost and minimal risk

Verifyhis/her understanding of the userrequirements through a graphical representationof the required system



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Abstraction

The process offocusingupon thosefeatures of something that are essential for

the task in hand, and ignoringthose

that are not. We build a model of something we are

interested in to provide an abstractedview of that thing.

Has great importance in moderndevelopment environment.



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Abstraction

We need to comprehend complexsituations

Focus upon those characteristics of the businesspertinent to the problem in hand

Disregarding those elements distinct from theproblem situation.

When modelling real world entitieseven more important that we considerthe entity (object) within a givencontext



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Abstraction example

Modelling a car:try and model it by its external characteristics

how it looks, how many doors it has etc.

- try and model it internal combustion engine -

how many valves it has, fuel injection system etc..

Depends upon the task in hand



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CAR: Racing car Red.Coupe. 5 doors. Sun roof.Alloy wheels. Tintedwindows. Leatherupholstery

CAR: 1.8 LX fuel injectionengine. ABSbreaking system.

Power AssistedSteering.

igure 1: Abstraction of a real-life object: CAR


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Three model view

All information systems can viewed fromthree different perspectives:

Dataoriented perspective

Process(function) oriented perspective

Behavioural(dynamic) oriented perspective



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Three model view

rocess

3 viewstogethermodel asystem



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Data modelling

Most important aspect of systemsdevelopment because:

Data is central to any informationsystem.

Values of data may change, basicstructure and types of data in organisation

remain (fairly) stable.



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Data modelling

Data modelling techniquesEntity relationship modelling

Developed into class diagramsintegrating data, methods andbehaviour



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Data modelling: ER Model



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Process modelling

Developing an accurate data model is a keyactivity but:

alone, it can not represent the way in which thebusiness works

to do this we need to understand what tasksmust be undertaken by the business, and howthey are performed.

This model: records the functionalrequirements of the proposed system not theinformation requirements.



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Process model: An example



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Behavioural modelling

Data + Process: Do not provide truerepresentation of an InformationSystem

When representing real world systemswe need to consider

how values change over

time.



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Data/process models: provide astatic view of an informationsystem.

In the real-world events occur andthese are translated intotransactionsin our information

system



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The behavioural (dynamic)aspects of the system are

about What happens to data as theresult of an event in the real

world, represented by atransaction in our informationsystem



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Behavior model example:State diagram



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Summary of systems developmentmethodologies

Hundreds exist

Many are a variation on a theme

A generic methodology has:A technicalbit (model)Tells you what tools and techniques to use

A managerialbit (model)Gives you a framework (or roadmap to follow)



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Development methodology

Its all about cookingA development method is like

a recipe, giving guidelines

You can follow the recipe and

produce a meal just like a topchef

Alternatively, you can follow therecipe and produce somethinginedible (even by the dog)!



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Where weve got to.

Development techniques have changedrapidly over the last 15 years The approach to systems development still

continues to evolve as we utilise newtechnology and software developmentapproaches

Development approaches for web-based projectsare poor

Many systems developed using system buildingtools



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Development methodology

Methodology

EvaluationFramework

Roadmap

Techniques &Tools



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Existing methodologies

In 1995 that over 1,000 brandname methodologies existed

A Jungle



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Existing methodologies

Today probably less than

100 methodologiesNumber offundamentally differentmethodologies evensmaller



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Some popular approachs

SSADM

JADFGR Summer 45ISE-Lecture2-


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There is some agreement

The important is not so muchabout methodology

You need to adaptyour recipeto the ingredients



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The future of methods

Ad hoc developmentNo formalised methodology usedExperienced developers use best of

approaches/tools/techniques they havepreviously encountered.



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Further development informal method areaO-O methods and web-basedmethods continue to be developed

Methods using UML toolset aredeveloped

Web-based methods?



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Adaptable methods

Methodologies that can be

adapted for differentenvironments

different to an ad-hocapproach: choice to mix-and-match but within adevelopment framework.



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The future?

Externaldevelopment

Avison & Fitzgerald see a

move towardoutsourcing.

Organisations not thenconcerned with

development issues -software house devisesown framework

ise-lecture2-methods_modelling.pptx

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