A class diagram shows the structure of a system through classes, attributes, operations, and relationships between classes. It includes classes and their properties like attributes and methods. It also shows relationships between classes like associations, aggregations, generalizations, and dependencies. The class diagram is a key tool in object-oriented analysis and design.

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A CLASS is a template (specification, blueprint)
for a collection of objects that share a common
set of attributes and operations.
Health Club Member
Class
Objects
attributes
operations
Defining Class

3. UML Class Diagrams 3
What is a Class Diagram?
•A Class Diagram is a diagram describing the
structure of a system shows the system's
•classes
•Attributes
•operations (or methods),
•Relationships among the classes.

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UML Class Diagram Notation
Class
Member
memberNumber
firstName
lastName
telephone
address
city
etc...
checkOutVideo
checkInVideo
buyItem
etc...
attributes
operations
{
{
Expanded view of a
Class into its three
sections:
Top: Class Name
Middle: attributes
Bottom: operations

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Object Association
n n
Class
Generalization
Relationship
Object
Aggregation
Association
0..*
1..*
Object Composition
Association
0..*
1
Will always be “1”
UML Class Diagram Notation

6. UML Class Diagrams 6
Essential Elements of a
UML Class Diagram
Class
Attributes
Operations
Relationships

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Association
Aggregation/Compostion
Dependencies
Generalization
Realization

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Associations
An association between two classes describes connection
among them.
If the association is between two classes then it is called
binary association.
There can be association among more than two classes.
It is represented by a solid line.
Example: “An Employee works for a Company”
Employee Company

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Class A Class B
role A
role B
Company Person
Employer
Employee
Example:
Associations

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Aggregation & Composition
•Aggregation (shared aggregation):
• is a specialized form of ASSOCIATION in which a whole is
related to its part(s).
• is known as a “part of” or containment relationship and follows
the “has a” heuristic
• three ways to think about aggregations:
• whole-parts
• container-contents
• group-members
• Composition (composite aggregation):
• is a stronger version of AGGREGATION
• the “part(s)” may belong to only ONE whole
• the part(s) are usually expected to “live” and “die” with the whole
(“cascading delete”)
• Aggregation vs. Composition vs. Association???

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Aggregation Composition
0..*
1..*
Faculty
CourseTeaching
1..*
1
SalesOrder
SalesOrderLineItem
(another: hand --> finger)(another: assembly --> part)
(team-teaching is
possible)

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Generalization
• Deriving a class out of a parent class having
some inherited property(from the parent
class) and some new property of the derived
class.
• The term generalization is for the
inheritance in the bottom to the up direction
i.e. from derived class to the parent class.

13. • It is represented by a solid line with a large
arrow head pointing towards the parent
class.
• Example:
13
Vehicle
Car Truck

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Dependency
• A dependency relationship is a weaker form
of relationship. A dependency states that a
change in specification of one class may
effect another class that uses first one but
not vice versa.
• It is represented by dashed lines.
Dependent class Reference class

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Realization
• Realization is very similar to inheritance
,the only difference between them is a class
is derived from an interface instead of a
base class.
• An interface is an abstract class.
Interface class Derived class

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17. UML Class Diagrams 17

18. UML Class Diagrams 18