2. 2
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.

4. 4
1 of 2
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

5. 5
2 of 2
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

7. 7
Association
Aggregation/Compostion
Dependencies
Generalization
Realization

8. 8
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

9. 9
Class A Class B
role A
role B
Company Person
Employer
Employee
Example:
Associations

10. 10
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???

11. 11
Aggregation Composition
0..*
1..*
Faculty
CourseTeaching
1..*
1
SalesOrder
SalesOrderLineItem
(another: hand --> finger)(another: assembly --> part)
(team-teaching is
possible)

12. 12
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

14. 14
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

15. 15
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

16. 16

17. UML Class Diagrams 17

18. UML Class Diagrams 18