Duration : 3 hrs

1

Ramakant SoniAssistant Professor

Dept. of Computer Science

B K Birla Institute of Engineering & Technology, Pilani, India

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Class Diagram Overview

Class diagram is one type of UML structure diagramwhich shows structure of the designed system at thelevel of classes and interfaces, shows their features,constraints and their relationships - associations,generalizations, dependencies, etc.

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ClassName

attributes

A class is a description of a set of objectsthat share the same attributes, operations,relationships, and semantics.

Graphically, a class is rendered as arectangle, usually including its name,attributes, and operations in separate,

operationsattributes, and operations in separate,designated compartments.

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ClassName

attributes

The name of the class is the only required tag in the graphical representation of a class. It always appears in the top-most compartment.

operations

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Person

name : Stringaddress : Addressbirthdate : Date

An attribute is a named property of a classthat describes the object being modeled.

In the class diagram, attributes appear in thebirthdate : Datessn : Id

In the class diagram, attributes appear in thesecond compartment just below the name-compartment.

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Person

name : Stringaddress : Address

Attributes are usually listed in the form:

attributeName : Type

A derived attribute is one that can becomputed from other attributes, but doesn’tactually exist.

address : Addressbirthdate : Date/ age : Datessn : Id

For example, a Person’s age can becomputed from his birth date. A derivedattribute is designated by a preceding ‘/’ asin:

/ age : Date

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Person

+ name : String# address : Address

Attributes can be:+ public# protected- private

# address : Address# birthdate : Date/ age : Date- ssn : Id

- private/ derived

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Person

name : Stringaddress : Addressbirthdate : Datebirthdate : Datessn : Id

Eat()Sleep()Work()Play()

Operations describe the class behavior and appear in the third compartment.

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A class may also include its responsibilities in a class diagram.

A responsibility is a contract or obligation of a class to perform a particular service.

SmokeAlarm

Responsibilities

-- sound alert and notify guard stationwhen smoke is detected.

-- indicate battery state

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In UML, object interconnections (logical or physical), are modeled as relationships.

There are five kinds of relationships in UML:

• dependencies

• generalizations

• associations

•Inheritence

•realization

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A dependency indicates a semantic relationship between two ormore elements. The dependency from CourseSchedule to Courseexists because Course is used in both the add and remove operations of CourseSchedule.

CourseSchedule

add(c : Course)remove(c : Course)

Course

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PersonA generalization connects a subclass to itssuper class.

It denotes an inheritance of attributes andbehavior from the super class to thebehavior from the super class to thesubclass and indicates a specialization inthe subclass of the more general superclass.

Student

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Student

UML permits a class to inherit from multiple superclasses, although some programming languages (e.g., Java) do not permit multiple inheritance.

Employee

TeachingAssistant

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If two classes in a model need to communicate with each other, there must be link between them.

An association denotes that link.

InstructorStudent

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