The document discusses system modeling as part of the requirements engineering process. It describes different types of models used to represent systems, including context models, behavioral models, data models, and object models. Specific modeling notations are introduced, such as data flow diagrams, state machines, and entity-relationship diagrams. Examples are provided to illustrate modeling concepts for systems like an ATM, order processing, and a microwave oven. The goal of system modeling is to help analysts understand system functionality from different perspectives to communicate requirements.

1. 33rdrd
UnitUnit
System modelsSystem models
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

2. ObjectivesObjectives
To explain why the context of a systemTo explain why the context of a system
should be modelled as part of the REshould be modelled as part of the RE
processprocess
To describe behavioural modelling, dataTo describe behavioural modelling, data
modelling and object modellingmodelling and object modelling
To introduce some of the notations used inTo introduce some of the notations used in
the Unified Modeling Language (UML)the Unified Modeling Language (UML)
To show how CASE workbenches supportTo show how CASE workbenches support
system modellingsystem modelling
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

3. Topics coveredTopics covered
Context modelsContext models
Behavioural modelsBehavioural models
Data modelsData models
Object modelsObject models
CASE workbenchesCASE workbenches
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

4. System modellingSystem modelling
System modelling helps the analyst to understandSystem modelling helps the analyst to understand
the functionality of the system and models arethe functionality of the system and models are
used to communicate with customers.used to communicate with customers.
Different models present the system from differentDifferent models present the system from different
perspectivesperspectives
–– External perspective showing the systemExternal perspective showing the system’’s context ors context or
environment;environment;
–– Behavioural perspective showing the behaviour of theBehavioural perspective showing the behaviour of the
system;system;
–– Structural perspective showing the system or dataStructural perspective showing the system or data
architecture.architecture.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

5. Model typesModel types
Data processing model showing how the dataData processing model showing how the data
is processed at different stages.is processed at different stages.
Composition model showing how entities areComposition model showing how entities are
composed of other entities.composed of other entities.
Architectural model showing principal subArchitectural model showing principal sub--
systems.systems.
Classification model showing how entitiesClassification model showing how entities
have common characteristics.have common characteristics.
Stimulus/response model showing theStimulus/response model showing the
systemsystem’’s reaction to events.s reaction to events.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

6. Context modelsContext models
Context models are used to illustrate theContext models are used to illustrate the
operational context of a systemoperational context of a system -- they showthey show
what lies outside the system boundaries.what lies outside the system boundaries.
Social and organisational concerns maySocial and organisational concerns may
affect the decision on where to positionaffect the decision on where to position
system boundaries.system boundaries.
Architectural models show the system andArchitectural models show the system and
its relationship with other systems.its relationship with other systems.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

7. The context of an ATM systemThe context of an ATM system
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

8. Process modelsProcess models
Process models show the overall processProcess models show the overall process
and the processes that are supported by theand the processes that are supported by the
system.system.
Data flow models may be used to show theData flow models may be used to show the
processes and the flow of information fromprocesses and the flow of information from
one process to another.one process to another.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

9. Equipment procurement processEquipment procurement process
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

10. Behavioural modelsBehavioural models
Behavioural models are used to describeBehavioural models are used to describe
the overall behaviour of a system.the overall behaviour of a system.
Two types of behavioural model are:Two types of behavioural model are:
–– Data processing models that show how data isData processing models that show how data is
processed as it moves through the system;processed as it moves through the system;
–– State machine models that show the systemsState machine models that show the systems
response to events.response to events.
These models show different perspectivesThese models show different perspectives
so both of them are required to describe theso both of them are required to describe the
systemsystem’’s behaviour.s behaviour.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

11. DataData--processing modelsprocessing models
Data flow diagrams (DFDs) may be used toData flow diagrams (DFDs) may be used to
model the systemmodel the system’’s data processing.s data processing.
These show the processing steps as dataThese show the processing steps as data
flows through a system.flows through a system.
DFDs are an intrinsic part of many analysisDFDs are an intrinsic part of many analysis
methods.methods.
Simple and intuitive notation that customersSimple and intuitive notation that customers
can understand.can understand.
Show endShow end--toto--end processing of data.end processing of data.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

12. Order processing DFDOrder processing DFD
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

13. Data flow diagramsData flow diagrams
DFDs model the system from a functionalDFDs model the system from a functional
perspective.perspective.
Tracking and documenting how the dataTracking and documenting how the data
associated with a process is helpful toassociated with a process is helpful to
develop an overall understanding of thedevelop an overall understanding of the
system.system.
Data flow diagrams may also be used inData flow diagrams may also be used in
showing the data exchange between ashowing the data exchange between a
system and other systems in itssystem and other systems in its
environment.environment.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

14. Insulin pump DFDInsulin pump DFD
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

15. State machine modelsState machine models
These model the behaviour of the system inThese model the behaviour of the system in
response to external and internal events.response to external and internal events.
They show the systemThey show the system’’s responses to stimuli sos responses to stimuli so
are often used for modelling realare often used for modelling real--time systems.time systems.
State machine models show system states asState machine models show system states as
nodes and events as arcs between these nodes.nodes and events as arcs between these nodes.
When an event occurs, the system moves fromWhen an event occurs, the system moves from
one state to another.one state to another.
Statecharts are an integral part of the UML andStatecharts are an integral part of the UML and
are used to represent state machine models.are used to represent state machine models.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

16. StatechartsStatecharts
Allow the decomposition of a model intoAllow the decomposition of a model into
subsub--models (see following slide).models (see following slide).
A brief description of the actions is includedA brief description of the actions is included
following thefollowing the ‘‘dodo’’ in each state.in each state.
Can be complemented by tables describingCan be complemented by tables describing
the states and the stimuli.the states and the stimuli.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

17. Microwave oven modelMicrowave oven model
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

18. Microwave oven state descriptionMicrowave oven state description
State Description
Waiting The oven is waiting for input. The display shows the current time.
Half power The oven power is set to 300 watts. The display shows ŌHalf powerÕ.
Full power The oven power is set to 600 watts. The display shows ŌFull powerÕ.
Set time The cooking time is s et to the userÕs input value. The display shows the cooking time
selected and is updated as the time is set.
Disabled Oven operation is disabled for safety. Interior oven light is on. Display shows ŌNot
readyÕ.
Enabled Oven operation is enabled. Interior oven light is off. Display shows ŌReady to cookÕ.
Operation Oven in operation. Interior oven light is on. Display shows the timer countdown. On
completion of cooking, the buzzer is sounded for 5 s econds. Oven light is on. Display
shows ŌCooking completeÕ while buzzer is sounding.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

19. Microwave oven stimuliMicrowave oven stimuli
Stimulus Description
Half power The user has pressed the half power button
Full power The user has pressed the full power button
Timer The user has pressed one of the timer buttons
Number The user has pressed a numeric key
Door open The oven door switch is not closed
Door closed The oven door switch is closed
Start The user has pressed the start button
Cancel The user has pressed the cancel button
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

20. Microwave oven operationMicrowave oven operation
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

21. Semantic data modelsSemantic data models
Used to describe the logical structure of dataUsed to describe the logical structure of data
processed by the system.processed by the system.
An entityAn entity--relationrelation--attribute model sets out theattribute model sets out the
entities in the system, the relationships betweenentities in the system, the relationships between
these entities and the entity attributesthese entities and the entity attributes
Widely used in database design. Can readily beWidely used in database design. Can readily be
implemented using relational databases.implemented using relational databases.
No specific notation provided in the UML butNo specific notation provided in the UML but
objects and associations can be used.objects and associations can be used.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

22. Library semantic modelLibrary semantic model
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

23. Data dictionariesData dictionaries
Data dictionaries are lists of all of the names usedData dictionaries are lists of all of the names used
in the system models. Descriptions of the entities,in the system models. Descriptions of the entities,
relationships and attributes are also included.relationships and attributes are also included.
AdvantagesAdvantages
–– Support name management and avoid duplication;Support name management and avoid duplication;
–– Store of organisational knowledge linking analysis,Store of organisational knowledge linking analysis,
design and implementation;design and implementation;
Many CASE workbenches support dataMany CASE workbenches support data
dictionaries.dictionaries.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

24. Data dictionary entriesData dictionary entries
Name Description Type Date
Article
Details of the published article that may be ordered by
people using LIBSYS.
Entity 30.12.2002
authors
The names of the authors of the article who may be due
a share of the fee.
Attribute 30.12.2002
Buyer
The person or organisation that orders a co py of the
article.
Entity 30.12.2002
fee-
payable-to
A 1:1 relationship between Article and the Copyright
Agency who should be paid the copyright fee.
Relation 29.12.2002
Address
(Buyer)
The address of the buyer. This is used to any paper
billing information that is required.
Attribute 31.12.2002
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

25. Object modelsObject models
Object models describe the system in terms ofObject models describe the system in terms of
object classes and their associations.object classes and their associations.
An object class is an abstraction over a set ofAn object class is an abstraction over a set of
objects with common attributes and the servicesobjects with common attributes and the services
(operations) provided by each object.(operations) provided by each object.
Various object models may be producedVarious object models may be produced
–– Inheritance models;Inheritance models;
–– Aggregation models;Aggregation models;
–– Interaction models.Interaction models.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

26. Object modelsObject models
Natural ways of reflecting the realNatural ways of reflecting the real--worldworld
entities manipulated by the systementities manipulated by the system
More abstract entities are more difficult toMore abstract entities are more difficult to
model using this approachmodel using this approach
Object class identification is recognised as aObject class identification is recognised as a
difficult process requiring a deepdifficult process requiring a deep
understanding of the application domainunderstanding of the application domain
Object classes reflecting domain entities areObject classes reflecting domain entities are
reusable across systemsreusable across systems
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

27. Inheritance modelsInheritance models
Organise the domain object classes into aOrganise the domain object classes into a
hierarchy.hierarchy.
Classes at the top of the hierarchy reflect theClasses at the top of the hierarchy reflect the
common features of all classes.common features of all classes.
Object classes inherit their attributes and servicesObject classes inherit their attributes and services
from one or more superfrom one or more super--classes. these may thenclasses. these may then
be specialised as necessary.be specialised as necessary.
Class hierarchy design can be a difficult process ifClass hierarchy design can be a difficult process if
duplication in different branches is to be avoided.duplication in different branches is to be avoided.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

28. Object models and the UMLObject models and the UML
The UML is a standard representation devised byThe UML is a standard representation devised by
the developers of widely used objectthe developers of widely used object--orientedoriented
analysis and design methods.analysis and design methods.
It has become an effective standard for objectIt has become an effective standard for object--
oriented modelling.oriented modelling.
NotationNotation
–– Object classes are rectangles with the name at the top,Object classes are rectangles with the name at the top,
attributes in the middle section and operations in theattributes in the middle section and operations in the
bottom section;bottom section;
–– Relationships between object classes (known asRelationships between object classes (known as
associations) are shown as lines linking objects;associations) are shown as lines linking objects;
–– Inheritance is referred to as generalisation and is shownInheritance is referred to as generalisation and is shown
‘‘upwardsupwards’’ rather thanrather than ‘‘downwardsdownwards’’ in a hierarchy.in a hierarchy.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

29. Library class hierarchyLibrary class hierarchy
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

30. User class hierarchyUser class hierarchy
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

31. Multiple inheritanceMultiple inheritance
Rather than inheriting the attributes and servicesRather than inheriting the attributes and services
from a single parent class, a system whichfrom a single parent class, a system which
supports multiple inheritance allows object classessupports multiple inheritance allows object classes
to inherit from several superto inherit from several super--classes.classes.
This can lead to semantic conflicts whereThis can lead to semantic conflicts where
attributes/services with the same name in differentattributes/services with the same name in different
supersuper--classes have different semantics.classes have different semantics.
Multiple inheritance makes class hierarchyMultiple inheritance makes class hierarchy
reorganisation more complex.reorganisation more complex.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

32. Multiple inheritanceMultiple inheritance
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

33. Object aggregationObject aggregation
An aggregation model shows how classesAn aggregation model shows how classes
that are collections are composed of otherthat are collections are composed of other
classes.classes.
Aggregation models are similar to the partAggregation models are similar to the part--ofof
relationship in semantic data models.relationship in semantic data models.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

34. Object aggregationObject aggregation
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

35. Object behaviour modellingObject behaviour modelling
A behavioural model shows the interactionsA behavioural model shows the interactions
between objects to produce some particularbetween objects to produce some particular
system behaviour that is specified as a usesystem behaviour that is specified as a use--
case.case.
Sequence diagrams (or collaborationSequence diagrams (or collaboration
diagrams) in the UML are used to modeldiagrams) in the UML are used to model
interaction between objects.interaction between objects.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

36. Issue of electronic itemsIssue of electronic items
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

37. Structured methodsStructured methods
Structured methods incorporate systemStructured methods incorporate system
modelling as an inherent part of the method.modelling as an inherent part of the method.
Methods define a set of models, a processMethods define a set of models, a process
for deriving these models and rules andfor deriving these models and rules and
guidelines that should apply to the models.guidelines that should apply to the models.
CASE tools support system modelling asCASE tools support system modelling as
part of a structured method.part of a structured method.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

38. Method weaknessesMethod weaknesses
They do not model nonThey do not model non--functional systemfunctional system
requirements.requirements.
They do not usually include informationThey do not usually include information
about whether a method is appropriate for aabout whether a method is appropriate for a
given problem.given problem.
The may produce too much documentation.The may produce too much documentation.
The system models are sometimes tooThe system models are sometimes too
detailed and difficult for users to understand.detailed and difficult for users to understand.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

39. CASE workbenchesCASE workbenches
A coherent set of tools that is designed toA coherent set of tools that is designed to
support related software process activitiessupport related software process activities
such as analysis, design or testing.such as analysis, design or testing.
Analysis and design workbenches supportAnalysis and design workbenches support
system modelling during both requirementssystem modelling during both requirements
engineering and system design.engineering and system design.
These workbenches may support a specificThese workbenches may support a specific
design method or may provide support for adesign method or may provide support for a
creating several different types of systemcreating several different types of system
model.model.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

40. An analysis and designAn analysis and design
workbenchworkbench
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

41. Analysis workbench componentsAnalysis workbench components
Diagram editorsDiagram editors
Model analysis and checking toolsModel analysis and checking tools
Repository and associated query languageRepository and associated query language
Data dictionaryData dictionary
Report definition and generation toolsReport definition and generation tools
Forms definition toolsForms definition tools
Import/export translatorsImport/export translators
Code generation toolsCode generation tools
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

42. Key pointsKey points
A model is an abstract system view.A model is an abstract system view.
Complementary types of model provideComplementary types of model provide
different system information.different system information.
Context models show the position of aContext models show the position of a
system in its environment with othersystem in its environment with other
systems and processes.systems and processes.
Data flow models may be used to model theData flow models may be used to model the
data processing in a system.data processing in a system.
State machine models model the systemState machine models model the system’’ss
behaviour in response to internal or externalbehaviour in response to internal or external
eventsevents
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net

43. Key pointsKey points
Semantic data models describe the logicalSemantic data models describe the logical
structure of data which is imported to orstructure of data which is imported to or
exported by the systems.exported by the systems.
Object models describe logical systemObject models describe logical system
entities, their classification and aggregation.entities, their classification and aggregation.
Sequence models show the interactionsSequence models show the interactions
between actors and the system objects thatbetween actors and the system objects that
they use.they use.
Structured methods provide a framework forStructured methods provide a framework for
developing system models.developing system models.
www.jntuworld.com
www.jntuworld.com
www.jwjobs.net