8/8/2019 Ch06 - GCU

1/21

1

Software Engineering: A Practitioners Approach, 7/eSoftware Engineering: A Practitioners Approach, 7/e

Chapter 6Chapter 6

Requirements Modeling:Requirements Modeling:Scenarios, Information, And Analysis ClassesScenarios, Information, And Analysis Classes

8/8/2019 Ch06 - GCU

2/21

Agenda Chapter 6

Requirements Modeling

Requirements Analysis

Scenario-Based Modeling Data Modeling

Class-Based Modeling

8/8/2019 Ch06 - GCU

3/21

3

Requirements AnalysisRequirements Analysis

Requirements analysisRequirements analysis specifies softwares operational characteristicsspecifies softwares operational characteristics

indicates software's interface with other system elementsindicates software's interface with other system elements

establishes constraints that software must meetestablishes constraints that software must meet

Requirements analysis allows the software engineer (called anRequirements analysis allows the software engineer (called ananalystanalystorormodelermodelerin this role) to:in this role) to: elaborate on basic requirements established during earlier requirementelaborate on basic requirements established during earlier requirement

engineering tasksengineering tasks

build models that depict user scenarios, functional activities, problembuild models that depict user scenarios, functional activities, problemclasses and their relationships, system and class behavior, and the flowclasses and their relationships, system and class behavior, and the flow

of data as it is transformed.of data as it is transformed. Requirements models provide a software designer with informationRequirements models provide a software designer with information

that can be translated to architectural, interface, and componentthat can be translated to architectural, interface, and component--level designs.level designs.

8/8/2019 Ch06 - GCU

4/21

4

A BridgeA Bridge

e

de ri i

i

de

de ig

de

The requirements model bridges the gap between a system-level description that describes overall system or business

functionality as it is achieved by applying software, hardware, data,human, and other system elements

and a software design that describes the softwares applicationarchitecture, user interface, and component-level structure.

8/8/2019 Ch06 - GCU

5/21

8/8/2019 Ch06 - GCU

6/21

6

ScenarioScenario--Based ModelingBased ModelingRequirements modeling with UML begins with the creationRequirements modeling with UML begins with the creation

of scenarios in the form of use cases, activity diagrams, andof scenarios in the form of use cases, activity diagrams, and

swimlane diagrams.swimlane diagrams.

8/8/2019 Ch06 - GCU

7/21

[Use[Use--cases] are simply an aid to defining what existscases] are simply an aid to defining what exists

outside the system (actors) and what should beoutside the system (actors) and what should be

performed by the system (useperformed by the system (use--cases). Ivar Jacobsoncases). Ivar Jacobson

(1) What should we write about?(1) What should we write about?

(2) How much should we write about it?(2) How much should we write about it?

Creating a Preliminary Use CaseCreating a Preliminary Use Case

(3) How detailed should we make our description?(3) How detailed should we make our description?

Refining a Preliminary a Use CaseRefining a Preliminary a Use Case

(4) How should we organize the description?(4) How should we organize the description?

Writing Formal Use CaseWriting Formal Use Case

7

ScenarioScenario--Based ModelingBased Modeling

8/8/2019 Ch06 - GCU

8/21

8

Developing a Preliminary UseDeveloping a Preliminary Use--CaseCase

List the functions or activities performed by the system by aList the functions or activities performed by the system by a

specific actorspecific actor

Two variations existsTwo variations exists

Narrative presentationNarrative presentation

Sequential presentationSequential presentation

Use cases of this type are sometimes referred to as primaryUse cases of this type are sometimes referred to as primary

scenarios.scenarios.

8/8/2019 Ch06 - GCU

9/21

9

Refining a Preliminary UseRefining a Preliminary Use--CaseCase

Alternative interactions (secondary scenarios) are essential for a completeAlternative interactions (secondary scenarios) are essential for a complete

understanding of the function that is being described by a use case.understanding of the function that is being described by a use case.

Secondary scenarios represent alternative interactionsSecondary scenarios represent alternative interactions

A set of secondary scenarios is obtained by evaluating primary scenario byA set of secondary scenarios is obtained by evaluating primary scenario by

asking following questions:asking following questions: Can the actor take some other action at this point?Can the actor take some other action at this point?

Is it possible that the actor will encounter some error condition at this point?Is it possible that the actor will encounter some error condition at this point?

Is it possible that the actor will encounter some other behavior at this point?Is it possible that the actor will encounter some other behavior at this point?

Alternative behavior is characterized as useAlternative behavior is characterized as use--case exception.case exception. An exception describes a situation that causes the system to exhibit somewhat differentAn exception describes a situation that causes the system to exhibit somewhat different

behaviorbehavior

8/8/2019 Ch06 - GCU

10/21

10

Writing a Formal UseWriting a Formal Use--CaseCase

Informal use cases are insufficient for describing a complex set of stepsInformal use cases are insufficient for describing a complex set of steps

with a significant number of exceptionswith a significant number of exceptions

A formal description of a use case includesA formal description of a use case includes Goal in contextGoal in context

PreconditionPrecondition

TriggerTrigger Scenario (list of actions)Scenario (list of actions)

ExceptionsExceptions

additional heading may be addedadditional heading may be added

8/8/2019 Ch06 - GCU

11/21

11

UseUse--Case DiagramCase Diagram

There is no need to create aThere is no need to create a

diagrammatic representation,diagrammatic representation,

however, it can facilitatehowever, it can facilitate

understanding, particularly whenunderstanding, particularly when

the scenario is complex.the scenario is complex.

8/8/2019 Ch06 - GCU

12/21

12

Activity DiagramActivity Diagram

SupplementsSupplements the usethe use--case bycase by

providing a diagrammaticproviding a diagrammatic

representation of the flow ofrepresentation of the flow of

interaction within a specificinteraction within a specific

scenario.scenario.

Adds additional detail notAdds additional detail not

directly mentioned (but implied)directly mentioned (but implied)

by the use case.by the use case.

8/8/2019 Ch06 - GCU

13/21

13

Swimlane DiagramsSwimlane Diagrams

A useful variation of the activityA useful variation of the activity

diagram that allows tdiagram that allows the modelerhe modeler

to represent the flow of activitiesto represent the flow of activities

described by the use case anddescribed by the use case and

at the same time indicate whichat the same time indicate which

actor (if there are multiple actorsactor (if there are multiple actorsinvolved in a specific useinvolved in a specific use--case)case)

or analysis class hasor analysis class has

responsibility for the actionresponsibility for the action

described by an activitydescribed by an activity

rectangle.rectangle.

8/8/2019 Ch06 - GCU

14/21

14

Data Modeling ConceptsData Modeling ConceptsData models depict the information domain for the problemData models depict the information domain for the problem

8/8/2019 Ch06 - GCU

15/21

8/8/2019 Ch06 - GCU

16/21

16

What is a Data Object?What is a Data Object?

AA datadata objectobject isis aa representationrepresentation ofof anyany compositecomposite

informationinformation thatthat isis processedprocessed byby software,software, ee..gg..,,

dimensionsdimensions

TheThe descriptiondescription ofof thethe datadata objectobject incorporatesincorporates thethedatadata objectobject andand allall ofof itsits attributesattributes..

AA datadata objectobject encapsulatesencapsulates datadata onlyonlytherethere isis nono

referencereference withinwithin aa datadata objectobject toto operationsoperations thatthat actact onon

thethe datadata.. DataData objectobject isis notnot thethe samesame thingthing asas objectobject--orientedoriented classclass

8/8/2019 Ch06 - GCU

17/21

17

Typical ObjectsTypical Objectsexternal entitiesexternal entities (printer, user, sensor)(printer, user, sensor)

thingsthings (e.g, reports, displays, signals)(e.g, reports, displays, signals)

occurrences or eventsoccurrences or events (e.g., telephone call, alarm)(e.g., telephone call, alarm)

rolesroles (e.g., manager, engineer, salesperson)(e.g., manager, engineer, salesperson)

organizational unitsorganizational units (e.g., division, team)(e.g., division, team)

placesplaces (e.g., manufacturing floor)(e.g., manufacturing floor)

structuresstructures (e.g., employee record)(e.g., employee record)

8/8/2019 Ch06 - GCU

18/21

18

Data AttributesData Attributes DataData attributesattributes definedefine thethe propertiesproperties ofof aa datadata objectobject

andand taketake onon oneone ofof threethree differentdifferent characteristicscharacteristics..

NameName anan instanceinstance ofof thethe datadata objectobject

DescribeDescribe thethe instance,instance, oror

MakeMake referencereference toto anotheranother instanceinstance inin anotheranother

tabletable..

OneOne oror moremore ofof thethe attributesattributes mustmust bebe defineddefined asas anan

identifieridentifier.. AttributesAttributes forfor aa givengiven datadata objectobject isis determineddetermined

throughthrough anan understandingunderstanding ofof thethe problemproblem contextcontext..

8/8/2019 Ch06 - GCU

19/21

19

RelationshipRelationshipDataData objectsobjects areare connectedconnected toto oneone

anotheranother inin twotwo differentdifferent waysways::

BasicBasic connectionconnection betweenbetween twotwo

relatedrelated objectsobjects

RelationshipRelationship withinwithin thethe contextcontext ofof

thethe softwaresoftware toto bebe builtbuilt

8/8/2019 Ch06 - GCU

20/21

20

ClassClass--Based ModelingBased ModelingClass modeling is a representation of the objectClass modeling is a representation of the object--orientedoriented

classes and the resultant collaborations that allow a systemclasses and the resultant collaborations that allow a system

to function.to function.

8/8/2019 Ch06 - GCU

21/21

21

ClassClass--Based ModelBased Model

A classA class--based model includesbased model includes

Classes and objectsClasses and objects

AttributesAttributes

OperationsOperations ClassClass--responsibilityresponsibility--collaborator (CRC) modelscollaborator (CRC) models

Collaboration diagramsCollaboration diagrams

PackagesPackages

Analysis classes, attributes, operations etc., areAnalysis classes, attributes, operations etc., are

identified by examining the problem statement.identified by examining the problem statement.