Class Diagram

Class Diagram

• A class diagram shows the existence of classes and their relationships in the logical view of the system.

• Graphical presentation of the static view.

Classes

• A class is represented as a three-part box• Class Name• Attributes

– At conceptual level it is a piece of information associated with the class that can be accessed and possibly modified

– Corresponds to a field at the implementation level

• Operations

- The processes the class can carry out (methods at implementation level)

- Basic operations (such as getValue) on attributes can be omitted (they can be inferred)

Classes

CustomerName address

Class Name

Attributes

Operations +creditRating():String

Attribute syntax: visibility name: type = defaultValue

Operation syntax: visibility name(parameter-list): return-type

Visibility:

- public +- protected #- private –

Class Names:- Simple - Path name (Package-name :: Class-name)

Window

Banking :: CheckingAccount

For abstract classes, class name is written in italic: Customer

Abstract Class

Abstract Operation

Class Diagram - Relationship

• Association: bi-directional semantic relationship• Aggregate: a whole and part relationship• Generalization: inheritance relationship• Dependency: single-directional relationship

between a client class and a supplier class/interface• Realize: single-directional relationship. A class

realizes the operations offered by the interface.

Construct Description Syntax

association a relationship between two or more classifiers that involves connections among their instances.

aggregation A special form of association that specifies a whole-part relationship between the aggregate (whole) and the component part.

generalization a taxonomic relationship between a more general and a more specific element.

dependency a relationship between two modeling elements, in which a change to one modeling element (the independent element) will affect the other modeling element (the dependent element).

Structural Modeling: Core Relationships

Construct Description Syntax

realization a relationship between a specification and its implementation.

Structural Modeling: Core Relationships (cont’d)

Associations

Associations are shown as lines between classes

• An association shows a relationship between instances of two classes

– Each association has two roles (one for each direction)

– A role can be explicitly named with a label

– Roles have multiplicity showing how many objects participate in the relationship

Associations can have multiplicities:

•A fixed value (such as 1 or 3)

•Many denoted by * (unlimited number)

•A range of values 0..1 or 3..*

•A set of values 2,4,8

• Adds attributes and operations to an association– Allows exactly one instance of the association

class between any two objects– Can use an actual class instead, if you need

more

Association Class

StudentCourse0..4 10..20

Grade

PersonCompany0..* 1..*

Job

descriptiondateHiredsalary

employeeemployer

Clerk ReservationConfirmation Number

1

qualifier

*finds

Qualified Association

• Association can be keyed by the value of the qualifier.

• A qualifier is used to reduce the scope of an association.

• A qualifier in an association solves the lookup problem.

Constraints

Bank TellerServes

Customer

{ordered }

High SchoolStudent

Chooses

Chooses{ or }

Academic

Commercial

• Represent further restrictions on associations or classes• A constraint is shown as a text string enclosed in braces

{ }.• A constraint is a restriction on one or more values of

(part of) an object-oriented model or system.

Meal

Soup Salad Main Course Dessert

- - - - - - - - { or } - - - - - - - - - - - - - - { precedes } - - - -1 1 1 1

Person Committee

1

* *

*

{ subset }

Member-of

Chair-of

ATM_WithdrawlATM_WithdrawlATM_WithdrawlATM_Withdrawl

customer : idcustomer : idamount : Moneyamount : Money{amount is multiple of $20}{amount is multiple of $20}

customer : idcustomer : idamount : Moneyamount : Money{amount is multiple of $20}{amount is multiple of $20}

AccountAccountAccountAccount

customer : idcustomer : idbalance : Moneybalance : Moneycustomer : idcustomer : idbalance : Moneybalance : Money

Aggregation and Composition

• Aggregation is a part-of relationship.

• Composition is also a part-of relationship, but part and whole live and die together

• In aggregation, parts may be added or removed, they may survive even after the whole is dead while in composition parts are contained in the whole and die with the container.

• Aggregation is more loosely coupled than composition.

Computer

Speaker CPU Keyboard Monitor Mouse

12 1 1 1

showsaggregation

Table

showscomposition

Table Top Leg

41

Generalization

• Sharing mechanism based on

a hierarchical relationship between classes.

• Subtype is a specialization

of the supertype.• Is-kind-of Relationship

CorporateCustomer

contactNamecreditRatingcreditLimit

remind()billForMonth(Int)

Customer

nameaddress

creditRating():String

PersonalCustomer

creditCardNumber

indicatesgeneralization

Generalization Relationship

vehicle

car shipamphibian

vehicle

water vehicleland vehicle

Dependency Relationship

Realization Relationship

• Realization is the relationship between a class and an interface. The class is said to realize the operations in the interface.