monash university, sims, semester one, 20051 modelling as a communication tool: introduction to...

Monash University, SIMS, Semester One, 2005Monash University, SIMS, Semester One, 2005 11

Modelling as a Communication Tool:Modelling as a Communication Tool:

Introduction to Process ModellingIntroduction to Process Modelling

CSE1204 - Information SystemsCSE1204 - Information Systems 11


The requirements specification The requirements specification documentdocument

Must be communicated to key stakeholdersMust be communicated to key stakeholders Should contain:Should contain:

Functions and services the system should provideFunctions and services the system should provideNon-functional requirementsNon-functional requirementsConstraints affecting the system’s development and Constraints affecting the system’s development and

operationsoperations Information about other systems the system must Information about other systems the system must

interface withinterface with System models are used to help understand the existing System models are used to help understand the existing

system and describe the proposed systemsystem and describe the proposed system


Example systemExample system

Easy Go HotelEasy Go Hotel

BOOKING

SAFE DEPOSIT

ROOMS

BEDS

01

makebooking

03

checkin

02

cancelreserv ation

04

check out

05

makesaf e

deposit


ModellingModelling Why do we do it?Why do we do it?

Our own understandingOur own understanding Communication with othersCommunication with others

How do we do it?How do we do it? informal techniquesinformal techniques formal techniquesformal techniques

How effective is it?How effective is it? different techniques for different purposesdifferent techniques for different purposes

eg. a road map, an organisation chart, a data flow eg. a road map, an organisation chart, a data flow diagramdiagram


Simplification in modellingSimplification in modelling all models are simplifications of the real world: they omit all models are simplifications of the real world: they omit

some features and emphasise otherssome features and emphasise others

this is called “abstraction”this is called “abstraction”

the choice of model and modelling method requires the choice of model and modelling method requires decisions about:decisions about: what things should be includedwhat things should be included what things can be omittedwhat things can be omitted


Representation in modellingRepresentation in modelling a model is a simulation: it is composed from a model is a simulation: it is composed from

something which represents realitysomething which represents reality

SuitabilitySuitability the choice of model and modelling method the choice of model and modelling method

requires decisions about the form of requires decisions about the form of representation that can best represent the real-representation that can best represent the real-life object being modelledlife object being modelled


Partitioning and level of detail in Partitioning and level of detail in modellingmodelling

partitioningpartitioning: all models simplify complex reality by breaking it : all models simplify complex reality by breaking it down into smaller, less complex parts which can be down into smaller, less complex parts which can be considered separatelyconsidered separately

partitioning allows the modeller to vary the amount of detail partitioning allows the modeller to vary the amount of detail which is given at different levels of the modelwhich is given at different levels of the model

the choice of model and modelling method requires the choice of model and modelling method requires decisions about:decisions about:

how to partition without losing the overall picture of the thing how to partition without losing the overall picture of the thing being modelledbeing modelled

how much detail can be included at each level of the modelhow much detail can be included at each level of the model


AudienceAudience

the suitability of different forms and languages for the suitability of different forms and languages for modelling will vary for different audiencesmodelling will vary for different audiences

all models assume some level of familiarity and all models assume some level of familiarity and understanding on the part of the audienceunderstanding on the part of the audience

the choice of model and modelling method requires the choice of model and modelling method requires decisions about which modelling form and language the decisions about which modelling form and language the target audience will best understandtarget audience will best understand


Purpose of modelsPurpose of models

all models are built to serve some purposeall models are built to serve some purpose

there is no ‘best’ model independent of any purposethere is no ‘best’ model independent of any purpose

the quality of a model is dependent on the purpose for the quality of a model is dependent on the purpose for which it was builtwhich it was built

the choice of model and modelling method requires an the choice of model and modelling method requires an understanding of the model’s purpose and decisions understanding of the model’s purpose and decisions about the best method for achieving that purpose about the best method for achieving that purpose


Models in analysis and designModels in analysis and design

in order to model a system, the systems analyst must in order to model a system, the systems analyst must choose an appropriate modelling form in terms of its:choose an appropriate modelling form in terms of its: audienceaudience purpose purpose degree of abstraction (simplification)degree of abstraction (simplification) form of representationform of representation level of partitioninglevel of partitioning level of detaillevel of detail


Modelling: for whom?Modelling: for whom?

System users and sponsorsSystem users and sponsors Saltwater Head Librarian; Shire Council; residents of Saltwater Saltwater Head Librarian; Shire Council; residents of Saltwater

Other systems analystsOther systems analysts Analysts who will help build the system Analysts who will help build the system

DesignersDesigners Designers of the finished systemDesigners of the finished system

Other technical staff - programmers, database builders, Other technical staff - programmers, database builders, systems administrators, etcsystems administrators, etc Code writers, database designers, help desk, technical supportCode writers, database designers, help desk, technical support


What can we use to build a What can we use to build a model?model?

words - written descriptionswords - written descriptionspictures - photographs, drawings, pictures - photographs, drawings,

diagrams, graphs, diagrams, graphs, mixed (words+pictures) - charts, mixed (words+pictures) - charts,

annotated drawings, maps,annotated drawings, maps,physical models - real life equivalents, physical models - real life equivalents,

scaled models, simulations scaled models, simulations


Model paraphernaliaModel paraphernalia

standardisation of symbols standardisation of symbols special modelling terminology/ rulesspecial modelling terminology/ rules

provides a “shorthand” way of conveying provides a “shorthand” way of conveying the model’s messagethe model’s message


What aspects can we model?What aspects can we model? to illustrate the relevant aspects of a system, we must use to illustrate the relevant aspects of a system, we must use

models of appropriate system componentsmodels of appropriate system components

for example, for a house we can model:for example, for a house we can model: its appearance (to show the look and feel)its appearance (to show the look and feel) the physical layout of rooms (to show functions)the physical layout of rooms (to show functions) the layout and connections between its structural components (to the layout and connections between its structural components (to

show the builders how to construct it)show the builders how to construct it)

What are the components of an information system which What are the components of an information system which we can use in a model to illustrate specific features of that we can use in a model to illustrate specific features of that system?system?


Modelling information systemsModelling information systems

Three aspects of information systems are typically Three aspects of information systems are typically modelled:modelled:

datadata what information is used in the system: what information is used in the system:

entity relationship diagrams, data structure diagramsentity relationship diagrams, data structure diagrams

processprocess what jobs use or manipulate data in the system:what jobs use or manipulate data in the system:

function decomposition, structure charts, data flow function decomposition, structure charts, data flow diagramsdiagrams

behaviourbehaviour what changes are wrought on information in the systemwhat changes are wrought on information in the system

entity life history diagrams, state transition diagramsentity life history diagrams, state transition diagrams


Problems in modellingProblems in modelling will other people interpret our models of the will other people interpret our models of the

world as we do?world as we do? what happens to things which we cannot model what happens to things which we cannot model

(exceptions; non-standard processes; errors)?(exceptions; non-standard processes; errors)? can we communicate all aspects of a system can we communicate all aspects of a system

satisfactorily using our standard modelling satisfactorily using our standard modelling techniques?techniques?

which models work best with which information which models work best with which information and which audience?and which audience?

standardisationstandardisation generalisationgeneralisation abstractionabstraction


Process modellingProcess modelling

processes are the “action” part of processes are the “action” part of businessesbusinesses

process modelling graphically represents process modelling graphically represents the processes which act on data to the processes which act on data to capturecapture manipulatemanipulate storestore distributedistribute


Process modellingProcess modelling

principal techniquesprincipal techniques function decompositionfunction decompositiondata flow diagramsdata flow diagrams

associated techniques for modelling the associated techniques for modelling the details of low-level processesdetails of low-level processesstructured Englishstructured Englishdecision tables and decision treesdecision tables and decision trees


Data Flow DiagramsData Flow Diagrams

model the flow of data into, through, and model the flow of data into, through, and out of an information systemout of an information system

represent an information system as a represent an information system as a network of communicating processesnetwork of communicating processesshow the processes that change or transform show the processes that change or transform

datadatashow the movement of data between show the movement of data between

processesprocesses


Example- As-u-go HotelExample- As-u-go Hotel

Make a reservationMake a reservationCheck inCheck inUse safe depositUse safe depositCheck outCheck out


01make

areserv ation

03use saf edeposit

02check in

04check

out

RESERVATION

OCCUPANCYGUEST

BED

SAFE DEPOSIT

Easy Go Hotel


Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)

a well-known techniquea well-known techniqueeasily understoodeasily understooda good communication toola good communication toolused to model both manual and used to model both manual and

automated processesautomated processesdescribed in Chapter 8 of the text book:described in Chapter 8 of the text book:

Whitten et al (2001)Whitten et al (2001)

Monash University, SIMS, Semester One, 2005

23

2

calculateprice

loan application

Products

Suppliers

Components of a DFD

• process

• data flow

• data store

• external agent


24

Gane & Sarson

DeMarco

Alternative sets of symbols

• process

• data flow

• data store

• external agent


2

calculateprice

ProcessProcess represents the work performed which represents the work performed which

changes datachanges data transforms incoming data flows into transforms incoming data flows into

outgoing data flowsoutgoing data flowshas a unique number and namehas a unique number and name


Naming processesNaming processes

name each process using a verb and a noun phrase:name each process using a verb and a noun phrase:

"calculate price""calculate price"

"validate customer details""validate customer details"

"accept supplier delivery”"accept supplier delivery” the name of a process should describe what the the name of a process should describe what the

process doesprocess does avoid vague names such as "process data”avoid vague names such as "process data” the number of a process is an identifier .. it does not the number of a process is an identifier .. it does not

indicate the sequence of processingindicate the sequence of processing


loan application

Data FlowData Flow represents data in motionrepresents data in motiondescribes a "packet" of data or data that describes a "packet" of data or data that

move togethermove togethermay consist of many individual, related may consist of many individual, related

elements that move together to the same elements that move together to the same destination destination


2

validatecustomer

order

customer order

valid customer order

invalid customer order

Naming data flowsNaming data flowsname each data flow using a noun or noun name each data flow using a noun or noun

phrasephrase the name should describe the contents the name should describe the contents

and should include as much information as and should include as much information as possible about the data flowpossible about the data flow


Data StoreData Store represents a collection of data flows at restrepresents a collection of data flows at rest has a unique name which should describe the has a unique name which should describe the

contents of the data storecontents of the data store may represent many different types of physical may represent many different types of physical

locations of datalocations of data may be a temporary or a permanent repository of may be a temporary or a permanent repository of

datadata

Sales Orders


30

data flows to and from a data store can remain unlabelled if all attributes in the store are moving, i.e. if an entire data packet (or packets) is going into or out of the data store

2

checksalesorder

Sales orders

3produceweekly sales totals

sales order

weekly salestotals

Data stores


Suppliers

External Agent (source/sink)External Agent (source/sink)

represents an entity in the environment with represents an entity in the environment with which the system communicateswhich the system communicates

a source if it is an origin of data coming into the a source if it is an origin of data coming into the systemsystem

a sink if it is a destination for data leaving the a sink if it is a destination for data leaving the systemsystem


External Agent (source/ sink)External Agent (source/ sink)

data flows connecting the external agents to the data flows connecting the external agents to the processes within the system represent the interface processes within the system represent the interface between the system and its environment between the system and its environment

external agents are outside the system and define external agents are outside the system and define its boundariesits boundaries

an external agent may be both a source and a sinkan external agent may be both a source and a sink what a what a sinksink does with data it receives from the does with data it receives from the

system and how a system and how a source source produces data which it produces data which it inputs to the system are outside the boundary of the inputs to the system are outside the boundary of the system and are not shown on the data flow diagram system and are not shown on the data flow diagram


1

editsalesorder

Sales orders

2

create purchase

order

sales orderCustomers

Suppliers

purchase order

1

Example Data Flow Diagram


ReferencesReferences

WHITTEN, J.L., BENTLEY, L.D. and DITTMAN, K.C. (2001) 5th WHITTEN, J.L., BENTLEY, L.D. and DITTMAN, K.C. (2001) 5th ed., ed., Systems Analysis and Design MethodsSystems Analysis and Design Methods, Irwin/McGraw-HilI, , Irwin/McGraw-HilI, New York, NY. Chapters 5, 7 and 8New York, NY. Chapters 5, 7 and 8

HOFFER, J.A., GEORGE, J.F. and VALACICH (2005) 4th ed., HOFFER, J.A., GEORGE, J.F. and VALACICH (2005) 4th ed., Modern Systems Analysis and DesignModern Systems Analysis and Design, Benjamin/Cummings, , Benjamin/Cummings, Massachusetts. Chapter 7Massachusetts. Chapter 7

monash university, sims, semester one, 20051 modelling as a communication tool: introduction to...

Documents

proposed system system

monash university

modelling method

modelling partitioning

proposed system slide

existing system

choice of model

example system easy