cb1004 modelling business systems 91 modelling business systems 9 other systems methods

CB1004 Modelling Business Systems 9

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Modelling Business Systems 9

Other Systems Methods

CB1004 Modelling Business Systems 9 2

Structure Oriented Development

Tasks are:Identify the data structures that make up the informationAnalyse the relationship between the components in terms of sequence, iteration and conditionDefine the processes to produce the components of the data structureMap the structural relationship of the data into a control hierarchy for the processes


Jackson Systems Design (JSD)

Seen as a bottom-up approachIgnores conventional views of the systems life cycle (SLC)Some authors e.g. Avison & Fitzgerald (1988) think it is not a complete method e.g. does not cover database design


JSD Stage 1(Entity/action) modelling

Identifies the entities and actions in the real world relevant to the IS

Entities Identifying these is difficult but they are often the nouns used in the description e.g. customer, supplier, order etc Must be uniqueMust perform actions or have actions performed upon them


ActionsMust take place at a point in time i.e. not be continuous i.e. conclude a sale NOT sellingMust take place in the real world - not be part of the information system that seeks to control it e.g. engage supplier NOT print supplier list


JSD Structure Diagram

Supplier

Register Product

movement *Deregister

Receipt o Return o


JSD Stage 2Network Stage

Initial model stageSpecify an information system to model and control these real world entities and actions (processes)Produces a systems specification diagram (SSD)

Processes identified in previous stage

Material and Parts control

Purchasing and supply


SSDNow consider the connections

Data stream connection – stream of sequential message e.g. text being keyed in connects two processes

Material and Parts control

Purchasing and supply

Partsrequest

Partsfor issue


SSDState vector connection – one process inspects the state of another process at a particular point in time

Produces a simulation model of the real world

StockPurchasing and supplySV


JSD 2 contNext step – function step

Define in structure language the processesOpen fileWhile not end of monthDo

Write page headingInitialise line countWhile not end of pageDo

Write lineIncrement line count

End while ………


Specify the required outputs and the defined inputs

Result is a logical modelDoes not consider

when information is neededwhen processes should run


JSD Stage 3Implementation stage

Converts the SSD into softwareStructure code basically similar to high level programming languages, hence conversion virtually automatic

Stage essentially about allocation and arrangement of processes and processors


Object Oriented Development

Creates a systemic software model of a real world situation made up of objectsSimilarity between objects and entities (JSD)But an object can be a concrete or abstract identifiable element or component of the problem domain (Booch 1991)


Object – other important kinds of objects are inventions of the design process whose collaborations with other objects serve as mechanisms that provide some higher level behaviour (Halbert & O’Brian 1988)

Inventions = conceptsThe design process – not abstract or impersonal, people make them workHigher level behaviour = holistic concept placed in the context of a hierarchy


OOS – major featuresHierarchy

Already seen the term ‘part of’; in OOS get ‘kind of’ – enables us to classify objects according to shared characteristics at increasing levels of abstractionEnables reuse of software of commonly shared characteristics

Reusable codeAllows for evolutionary systems development based on learning


Objects and their properties

State Look at a specific object – quantity sold

Property is static because it is unlikely to be changed to anything else e.g. quantity boughtValue is dynamic – different values through time

BehaviourChanges of state it undergoes as a result of passing and receiving messages to and from other objects



Object identityMore than the nameIncludes the properties that make it what it is

RelationshipsUsing relationships – concerned with process

Objects seen in terms of how they affect one anotherControl function might send a message to another object to check on a value and receive feedback information

Containing relationships- concerned with structure

Aggregation of relationships within a systemic hierarchyA cupboard consists of components e.g doors


Relationships

Stock controller

Cupboard

Door

Container unit

SC uses the cupboard to check its availabilityCupboard has a containing relationship with its components



Class and class hierarchiesDepends on the view of the developer

Which is the odd one out: Dog, cat television?View

Animal orWhich needs a licence

Class depends on the properties


Class and inheritanceA class shares the structure or behaviour defined in one (single) or more (multiple) other classes (super classes)


Inheritance

Animals

Reptiles Mammals

Lizards Snakes Cats Dogs

4 legged animals


Single inheritanceCats and dogs inherit behaviour e.g. suckling young from the mammal super class

Multiple inheritanceStructure and behaviour of being a 4-legged animal that suckles its young


Meta-class relationshipsClasses can themselves be regarded as objectsLeads to classes of classesClasses are objects BUT objects are not classes


The OO modelIdentify classes and objects

Depends on the purpose of the development so no particular techniqueIndicated by nouns or names

Defining the semantics of classes and objects

Establish activities and behaviour; again no techniqueIndicated by verbs


Identifying relationships between classes and objects

Classes – identify inheritance, using and other relationshipsObjects – establish static and dynamic properties

Implement classes and objectsCreate the software model

OO is NOT a structured method


Some OO diagramming techniques #

Class diagramsWhat classes exist and their relationships

Object diagramsSpecifies mechanism used to regulate how objects collaborate

State Transition DiagramsSpecifies how the time ordering of external events can affect the state of each instance of a class

Module diagramsPhysical packaging of classes and objects into software modules


OO SoftwareOO forms of PascalC++ (development of C)CLOS (Common Lisp Object System)SmalltalkEiffel


Prototyping First version of a system to be modified after testingGuide to development of other components within the systemConcerned

Not with does it work?BUT does it work the way you want it to?


PrototypingUseful in the context of structured design to develop e.g. printouts, screens etcUses 4GLsGUIs (graphical user interfaces)


Integrated methodsDeveloped as a result of problems with individual approachesMultiview (Wood-Harper 1985) #

Analysis of human activatesSSM as far as the conceptual model

Analysis of entities, functions and events

Follows mainstream IS development concepts as previously mentioned


Multiview cont.Analysis and design of sociotechnical system

Recognises that all change involves conflict of interest

Looks at employees needs and wantsCreates a fit between the employee and employer

Knowledge fit – employees should believe their skills and worth are being adequately usedPsychological fit – conforming to employees view of their aspirationsEfficiency fit – balancing financial rewards to employees against requirements of the employerTask structure – reflecting the success in making the job appropriately demanding and fulfilling for the employeeEthical fit between employee and employer


Multiview cont.Design of human computer interface

How computers and humans will interact

Design of technical subsystemsChoice of hardware and software

cb1004 modelling business systems 91 modelling business systems 9 other systems methods

Documents

jackson systems design

jsd stage

real world entities

real world situation

real world relevant

real worldstockpurchasing

simulation model

information system