Basics of UML Class Diagrams
• What is a UML class diagram? Imagine you
were given the task of drawing a family tree.
The steps you would take would be:
– Identify the main members of the family
– Identify how they are related to each other
– Find the characteristics of each family member
– Determine relations among family members
– Decide the inheritance of personal traits and
Basics of UML Class Diagrams
• A UML class diagram is similar to a family tree.
• A class diagram consists of a group of classes and
interfaces reflecting important entities of the business
domain of the system being modeled, and the
relationships between these classes and interfaces.
• The classes and interfaces in the diagram represent the
members of a family tree and the relationships
between the classes are analogous to relationships
between members in a family tree.
• Interestingly, classes in a class diagram are
interconnected in a hierarchical fashion, like a set of
parent classes (the grand patriarch or matriarch of the
family, as the case may be) and related child classes
under the parent classes.
Basics of UML Class Diagrams
• Similarly, a software application is comprised of
classes and a diagram depicting the relationship
between each of these classes would be the class
• By definition, a class diagram is a diagram
showing a collection of classes and interfaces,
along with the collaborations and relationships
among classes and interfaces
• A class diagram is a pictorial representation of the
detailed system design
• Now you now know what a class diagram is. But,
how does a class diagram relate to the use case
diagrams that that we learned before?
Basics of UML Class Diagrams
• When you designed the use cases, you must
have realized that the use cases talk about
"what are the requirements" of a system.
• The aim of designing classes is to convert this
"what" to a "how" for each requirement
• Each use case is further analyzed and broken
up into atomic components that form the
basis for the classes that need to be designed
Elements of a Class Diagram
• A class diagram is composed primarily of the following
elements that represent the system's business entities:
– Class: A class represents an entity of a given system that
provides an encapsulated implementation of certain
functionality of a given entity. These are exposed by the
class to other classes as methods
– Apart from business functionality, a class also has
properties that reflect unique features of a class. The
properties of a class are called attributes.
– As an example, take a class named Student.
• The Student class encapsulates student information such as
student id #, student name, and so forth. Student id, student
name, and so on are the attributes of the Student class. The
Student class also exposes functionality to other classes by using
methods such as getStudentName(), getStudentId(),
Elements of a Class Diagram….
• A class is represented by a rectangle. The
following diagram shows a typical class in a
class diagram:
Elements of a Class Diagram….
– Interface: An interface is a variation of a class. As
we saw from the previous point,
– a class provides an encapsulated implementation
of certain business functionality of a system. An
interface on the other hand provides only a
definition of business functionality of a system. A
separate class implements the actual business
– An interface shares the same features as a class; in
other words, it contains attributes and methods.
The only difference is that that the methods are
only declared in the interface and will be
implemented by the class implementing the
Elements of a Class Diagram….
– Package: provides the ability to group together
classes and/or interfaces that are either similar in
nature or related.
– Grouping these design elements in a package
element provides for better readability of class
diagrams, especially complex class diagrams.
Figure —a package
Relationship Between Classes
• The following table shows the kinds of relationships
between classes, their notation, and what they mean
Relationship Between Classes….
The UML Class Diagram in Action
Case study—Courseware Management System
• In the use case lecture, we identified the primary
actors and use cases in the use case model of the case
• Let us recap the analysis that was performed when the
use case model was designed.
• The following terms and entities specific to the system
were identified from the problem statement:
– Courses and Topics that make up a course
– Tutors who teach courses
– Course administrators who mange the assignment of the
courses to tutors
– Calendar or Course Schedule is generated as a result of
the Students who refer to the Course schedule or
Calendar to decide which courses for which they wish to
sign up
The UML Class Diagram in Action….
Case study—Courseware Management System
• The potential actors of the system were:
– Tutors
– Course administrators
– Students
• And the use cases of the system were:
View courses
Manage topics for a course
Manage course information
View course calendar
View tutors
Manage tutor information
Assign courses to tutors
The UML Class Diagram in Action….
Identifying classes of the Courseware Management System
• Identify the "active" entities in the system
– So, our first list of classes in the system appears to
– Course administrators
– Tutors
– Students
• Identify business domain ("passive") entities
in the system
– These entities reflect the business domain and
hence are potential classes for our system.
– Courses
– Topics that make up a course
– Course calendar generated
The UML Class Diagram in Action….
Identifying classes of the Courseware Management System
• So, the list the list of classes and interfaces
that we have identified in the Courseware
Management System.
Course Administrator
Course Calendar
The UML Class Diagram in Action….
Identifying methods of the Courseware Management System
• The classes that we have identified for the
Courseware Management System also provide
business functionality related to the
• Example the courseadministrator class have
the following functionality (methods):
The UML Class Diagram in Action….
Identifying methods of the Courseware Management System
• Other classes have methods as shown in the
figure below?
The UML Class Diagram in Action….
Identifying relationship and drawing the class diagram
Other examples of Class Diagrams
• Seminar Management System