cb1004 modelling business systems 71 modelling business systems 7 systems methods

CB1004 Modelling Business Systems 7

1

Modelling Business Systems 7

Systems Methods

CB1004 Modelling Business Systems 7 2

Systems Life Cycle – Waterfall Model

Requirements Analysis

PreliminaryDesign

DetailedDesign

Code and Unit TestingIntegration andAcceptance Test

Installation andTurnover

Operation andMaintenance

SystemRequirements

Analysis

Rework

Products

Credit: W.W. Royce, 1970


Role of soft systems analysis

Why is it relevant?Looking at the management system and the whole business or organisational system involves sorting human and policy issues

What is the relationship between soft systems and information systems development methods?

At the start of a system, we don’t know what we are developing, hence soft system analysis would be carried out at the beginning


Are methods applied to soft systems different to those applied to hard systems?

Similar concepts e.g. stages, deliverables, iterations, tools and techniques, but with soft systems there are differences due to the nature of the problemSoft systems concerned with defining the nature of the problem not offering solutions

Hard issues solved by measurement, computation, observation, technical meansSoft issues solved by negotiation, persuasion, compromise


Soft systems method (SSM)

Peter Checkland (1981)A methodology that brings about improvement in areas of social concern (von Bulow, 1989)Not an information system development methodThe early 7 stage form # (Checkland 1981) evolved into the later form # (Checkland & Scholes, 1990)Look at the conventional 7 stage model using Mike Harry’s dog registration case#


1 Situation unstructuredSession 2 given a rich picture of this case#A rich picture includes all aspects of a situation

Visible &audibleSilent, invisible things e.g. smellsAbstract, emotional things e.g. social atmosphere


2 Situation analysedIdentifies the themes and issues from the rich picture #Themes – relate to actual processesIssues relate to concerns generated in wider activities


3 Relevant system and root definitions

The qualities we want the system to possessE.g Identification (relevant system)

An officially enforced system to identify approved owners of dogs (root definition)

How do we know this is a good definition: CATWOE #


CATWOEAn officially enforced system to identify approved owners

of dogs Customers –owners identified? Ambiguous because not explicit who are the recipients or victims of the outputActors – not clear; needs something to say who will be carrying out the systemTransformation process – clear that the system transforms unidentified dog owners into identified ones; is there an implied ‘approval’ process?


CATWOE An officially enforced system to identify approved owners

of dogs Weltanschauung – ‘officially enforced’ is clear that this system has a strong authoritarian world viewOwner – ‘officially enforced’ implies it is owned by officialdomEnvironment – officially enforced’ implies in the context of a legal environment but does not cover the social environment in which it will have to operate


Improved root definitionA legally enforceable agency system to record dog ownership


4 Conceptual modelsShows the sequence and co-ordination of activities to be carried out to meet the root definition #


5 ComparisonCan use a matrix# to check each activity in the conceptual model to see if it exists in the real-world

Results then focus on what should be done about it

Absence of activity – a clear indication we need to make it happen?Trying to find out if it exist may reveal we don’t yet know


6 DebateAgenda generated from comparisonWill lead to action for change


7 ImplementationImplementing change


Developed SSM (DSSM)Two analysis stream

Logic basedSequence of task issues, relevant systems, root definitions etc

Cultural analysis Recognises the process of applying SSM becomes part of the existing situationHeisenberg’s Uncertainty PrincipleRecognises 3 area as a culture

The activity of intervention itselfThe ‘social system; in the problem situationThe ‘political system’ in the problem situation


Intervention seen in 3 rolesThe client – requested the studyThe problem solverThe problem owner

Social systemMix of human relationships, both formal and informal

Political systemPossession, exchange, clash and resolution dimensions


Process oriented development

Examples include structured analysis methods of Gane and Sarson (1979) and de Marco (1979), couple with structured design methods of Yourdon and Constantine (1978)

Structure – clear stage with deliverableTop down methods: what the system must be ->what it should do -> how it should be constructed

Transforms raw data (input) into information (output)


SSADMStructured systems analysis and design methodSelected in 1981 as a mandatory method for UK Government projectsComprehensive method not requiring a high level of skill to learn but needing guidance from an experienced user


SSADM toolsData flow diagrams (DFDs)

Data flows, data store and processes used by the system with external entities (sources and destinations for data outside the system)

Logical data structures (LDS) show how data combines to form informationEntity life histories (ELH) shows how information is changed during its lifetime in relation to the entity to which it refers


DFDsLook at Arbor sales, purchases and operations departmentsIdentify

External entities to ArborData flows

Context diagram#


DFDs contLook at the box Arbor Corporate systemIdentify

Departments within ArborData flows between them and the externals

Level 1 DFD #


DFDs cont.Look at the process ‘Process sales’ (and the notesIdentify

External entitiesProcessesData storesData flows

Level 2 DFD #


SSADMStages, tools and techniques #1 Analysis

Understand the current system and how it worksIdentify the problems with the current systemIdentify additional requirements for the new system


2 specification of requirements

Compares the existing physical system against the problems and requirements list

Identifies Business System Options (BSO) – improvements to the system that meet the user requirementsSelection of a BSO leads to a logical view of the required system


3 Selection of technical options

Identifies technical options and hence limitations e.g. real time or batch processing system


4 Logical data design5 Logical process designUsually run in parallel

Defining the way we access data (process) will depend upon how that data is arranged (structure)


6 Physical designTurns the logical view of the system into a physical implementation

Dependent on system software used

cb1004 modelling business systems 71 modelling business systems 7 systems methods

Documents

hard systems

problemsoft systems

soft systems different

organisational system

management system

soft system analysis

enforceable agency system

unidentified dog owners