Object Oriented Methods.pdf

Object-Oriented Methods, School of Computer Science and IT, University of Nottingham 1

Class Diagrams (Relational Elements)

Generalisation, Specialisation

DefinitionInheritance is a relation between superclasses and subclasses whichenables attributes and operations of a superclass to become accessibleto its subclasses.

Description• superclass/subclass

• Discriminator denotes the aspect relevant for hierarchical structuringof the properties.

• Partition is an entirety of subclasses based on the same discriminator.

Notation


Different views of generalisation:

• conceptual view:all instances of a subclass are also instances of superclass

• specification and implementation views:imply a specification of the operations that must be supportedby its subclass

Multiple classification

• Multiple classification allows multiple types for an object(not supported in Java and in C++)

legal combinations of subtypes: (Female, Patient, Nurse),(Male, Physiotherapist), (Female, Patient), (Female, Doctor, Surgeon)

illegal combinations: (Patient, Doctor), (Male, Doctor, Nurse)


Multiple InheritanceProblems:1. Name collision: two or more different superclasses use

the same name for some of their propertiessolution: address their property in a fully qualified way

2. Repeated inheritancesolution: superclass is not replicated

Person

Teacher Researcher

Professor

WaterVehicle

draughtdisplacement

WindpoweredVehicle

minWindForcemaxWindForce

Vehicle

namemanufacturer

MotorVehicle

fuelTypepower

SailingBoat

surfaceOfSailsnumberOfSails

{overlapping}

Overlapping versus Disjoint

� It is acceptable for one class to specialiseboth the overlapping subclasses of Boat!

• Overlapping


WaterVehicle

draughtdisplacement

WindpoweredVehicle

minWindForcemaxWindForce

Vehicle

namemanufacturer

MotorVehicle

fuelTypepower

SailingBoat

surfaceOfSailsnumberOfSails

{disjoint}

� This specialisation is not correct!An object cannot be an instance of bothWaterVehicle and WindpoweredVehicle!

• Disjoint

Constraints on generalisation:• overlapping• disjoint• complete• incomplete

Superclass

Subclass1 Subclass2

{incomplete}


Association

DefinitionAssociation describes a connection between classes.

Description• Links are instances of an association.• Recursive association• Aggregation, composition

Notation• Multiplicity of an association specifies the number of objects of the

opposite class with which an object can be associated.• Roles• Constraints

Class A Class Brole a role b

1 *

<<Stereotypes>>RelationName{Constraint/TaggedValues}

Multiplicity

�


Example

• Examples of multiplicity specifications:10, 10..43, 70..* (default)*1..*0..3, 7, 9..*

Implementation: assign appropriate reference attributes to theinvolved classes.

Company

nameaddress

Employee

nameaddressstaffNo*11

employeeemployer

*

employs

works for

�

�

• role name• multiplicity

Personal Customer

creditCard#

Customer

nameaddress

creditRating():String

Order

dateReceivedis Prepaidnumberprice

dispatch()close()

1

Product

Order Line

quantity:Integerprice:MoneyisSatisfied:Boolean

*

1

*11

*

1

line items*

* 1

Corporate Customer

contactNamecreditRatingcreditLimit

remind()billForMonth(Integer)

Employee

0..1

*

0..1

*

sales rep

{if Order.customer.creditRatingis "poor" then Order.isPrepaidmust be true}

{creditRating() == "poor"}


• Interface for an Order class:

class Order {public Customer getCustomer() ;public Set getOrderLines() ;…

• Implementation model

class Order {private Customer _customer ;private Set _lineItems ;

class Customer {private Set _orders ;

Personal Customer

creditCard#

Customer

nameaddress

creditRating():String

Order

dateReceivedis Prepaidnumberprice

dispatch()close()

1

Product

Order Line

quantity:Integerprice:MoneyisSatisfied:Boolean

*

1

*11

*

1

line items*

* 1

Corporate Customer

contactNamecreditRatingcreditLimit

remind()billForMonth(Integer)

Employee

0..1

*

0..1

*

sales rep

{if Order.customer.creditRatingis "poor" then Order.isPrepaidmust be true}

{creditRating() == "poor"}

• navigability– unidirectional– bidirectional


Dependency Relations

DefinitionDependency is a relation between two model elements whichshows that a change in one element requires a change in the other.

Description• Influences the order of compilation.

Notation

dependent independent

Example

• Class uses an interface of another class.

• Class is dependenton another class.

• Operation is dependenton a class.

• Package is dependent on another package.


• parameter reference

• creation of object

☛ do not imply an associationthey are modelled with dependencies !

Recursive Associations

DefinitionRecursive associations are associations in which only one class isinvolved.

Example

Employee

namestaffNoroomNo

office clerk

*

manager 1

leads

reports to�

�


Attributed Association

DefinitionAttributed association is a model element which has both the propertiesof a class and an association.

Description• Association class

Notation

Class A

Association

Class BAssociation

Association class

Enterprisename

address

Employmentfrom:Date

to:Date

Employeename

address

1..* *

Association attributes

Example•Two involved objects may at most have one relation with each other.


Class A

Associationclass

Class B

Class A Class B

Class C

1 1

1..*

*1..*

*

promoting an association classto a full class

Enterprise Employee

Employmentfrom: Date

to: Date

1

* 1..*

1

• Promoting an association class to a full class enablesan Employee to have more than one Employment withthe same Enterprise.


Skill

Competency

Employee* *

• Employee is not allowed to have more than one Employmentwith the same Enterprise

☛ use an association class• Employee is allowed to have more than one Employment

with the same Enterprise☛ use a full class

• Employee has one competency in the same skill☛ use an association class

Association Constraints

• Ordered association{ordered}{ordered by contract date}

Employee

nameaddress

1

{disjoint periods ofemployment}

Enterprise

nameaddress

Employment

from:Dateto:Date1..*

1

has

11

has

*

�

�


Qualified Associations

DefinitionA qualified association is an association in which qualifying attributesare used to subdivide the referenced set of objects into partitions, whereeach partition may occur only once.

Description• UML counterpart to the dictionary

Notation and Example

• Multiplicity always refers to one partition.


Interface for the class Enterprise:

class Enterprise {public Employee getEmployee(String anInitial) ;public void addEmployee(String anInitial, String name) ;private map _Employee ;…

}

Derived Associations

DefinitionDerived association is an association which is calculated when required.

Description• Concrete object relations are derived from the values of other

object relations and their objects.


employer 1

*

Enterprise Department

1 *

Employee

*

1

/works for*

1

employer

1 *belongs to

department

*

1

works in

�

�

�

{Employee.employer =Employee.department.employer}


N-ary Associations

DefinitionMore than two association rules are involved.

Description, Notation and Example

Train1 Feb, T11 Feb, T2

PassangerJohn MrMark DrJoana Ms

SeatC1, S1C1, S2

• Here, it is possible to navigate to an association not coveredby the original association occurrences.

Train

datetrain

Passanger

nametitle

1..*

1

Seat

carraigeNoseatNo

1..*1

1..*

1..*

1..*1

1..*

1

1..*

1..*


• Multiple Association

• N-ary associations can be transformed into normal associations.


Directed Associations

DefinitionDirected association is an association in which you can directlynavigate from one of the involved association roles to the other,but not vice versa.

Notation• Multiplicity and role names are relevant on the side of the association

towards which navigation is possible.

Example

Person Car0..*

is taking

5

�

Aggregation

DefinitionAggregation is an association in which the involved classesrepresent an entirety-part hierarchy.

Description• Propagation of operations• Composition

Notation

PartEntiretyconsists of

1

�

* BankAccountAddress

Customer


Composition

DefinitionComposition is a strict form of aggregation, in which the partsare existence-dependent on the entirety.

Description• Cardinality on the side of the aggregate can only be 1.• Each part is part of exactly one composition object.

Notation

PartEntirety

Existence-DependentPart

Aggregation

Composition

Constraints

DefinitionConstraint is an expression which restricts the possiblecontents, states or the semantics of a model element.

Description• legal set of values of an attribute• pre- or postconditions for messages or operations• special context for messages or relationships• specific order• chronological condition...

Notation{constraint}dependency relationnote


Example

• Dependency

• Consistency

Project

Employee

has consistsof

{subset}

1 1..*

Customer

Invoice Contract

1

0..*

1

0..*

has

based on

receives

�

�

�

project Leader projectMembers

1

Invoiceself.contract.customer = self.customer

• OR

• Values

PersonDomesticaddress

Foreignaddress

has

has�

�

{or}

*

*

Rectanglea {a>0}b {b>0}


• Order

• Formulae

Person

lastNamefirstName

NameList

1 1..*

contains

{ordered:lastName} 1..*1

Person

birthDate:Date/age {age=today-birth}

Person

birthDate:Date/ age

{/age=today-birthDate}

�

• Enumerationcolour : {red, blue, green}

Responsibility?

Class ShoppingSpree {private Vector participantSet ;public void addParticipant(Person : participant) {

if (participant.age > 65) {participantSet.addElement(participant) ;

}}

...}

Person

ageShoppingSpree

1 1..*

{participant.age>65}

participants1..*


Tagged Values

DefinitionTagged values are keyword/value pairs which extend the semantics ofindividual model elements.

Description• influence code generation

– abstract for classes and operations– readonly for attributes– private for attributes and operations– obsolete– information on author, version number

Notation

Examples{private}{Author=Tara King}{transient}{persistent}

GeomFigure{abstract Version=1.3}

visible:Boolean {readonly}display() {abstract}remove() {abstract}getPosition(): PointsetPosition(p: Point)

setPos(x,y) {obsolete}


Stereotypes

DefinitionA stereotype is used as a means of specifying that amodelling element conforms to the well understoodpattern of behaviour.

Description• specify possible usage contexts of a class, a relationship

or a package• model element can be classified with an arbitrary number of

stereotypes• code generation

Types of stereotypes:• decorative• descriptive• restrictive• redefining

Notation

Examples• meaning of a class in the application architecture:<<domain class>>

<<model>>, <<view>>, <<controller>>,<<enumeration><overlapping>>, <<disjoint>>, <<implements>>, <<include>>,<<extend>>

Customer

<<actor>>Customer

<<actor>>Customer

<<actor>><<boundary>>


<<DomainClass>>Circle

positionvisible

display()remove()

<<Information>>isVisible()

<<AttributeAccess>>getPosition()

setPosition(newPos)

Notes

DefinitionNotes are comments to a diagram or an arbitrary element in a diagram,without any semantic effect.

Descriptioninformation on: development state,

version of a class,developer responsible for the class or its lastmodificationproject management...


invPosition

quantityitemunitPrice

total

Invoice

invPositions:Set

sumPositions()sumVAT()

1 *1 *

"This example is inJava"


Packages

DefinitionPackages are collections of model elements which are used tostructure the entire model into smaller units.

Descriptions

• built on the basis of logical or physical relationshipsPackageName::ClassName

• <<global>> all packages in the system have a dependencyto this package•



☛ dependencies between packages are not transitive

• generalisation: a package must conform to the interface ofthe general package


Refinement or Realisation Relations

Definition• Refinement relations are relations between similar elements of

different degrees of detail.• Realisation relations are relations between interface and its

implementation.

DescriptionRefinement• analysis / design version of a model element• clean / optimised version of a model element

Example

String

isEqual(String):BooleanisGreater(String):Booleanlength():Integer

<<interface>>Sortable

isEqual(object):BooleanisGreater(Object):Boolean

Tariffing Tariffing1

Performanceoptimised


Summary

• Class diagrams support static modeling.

• Class diagrams depict classes and relationships between them.

Documents

Object Oriented Methods.pdf