1. A class diagram shows classes, attributes, operations, and relationships between objects in a system. It describes the static structure of the system. 2. The main components of a class are its name, attributes, and operations. Relationships include association, dependency, generalization/inheritance, and realization. 3. Association examples include unidirectional, bidirectional, reflexive, and aggregation. Aggregation differs from composition based on whether parts can exist independently of the whole.

1. Session 13: Class Diagram
R2S Academy – Internal Use – Author: TUAN NGO

2. Table of Content
Class Diagram - Definition
Examples
Practice & Exercises
R2S Academy – Internal Use – Author: TUAN NGO
1
2
3
Objectives

3. Definition
Class Diagram

4. Class Diagram
Definition

5. Class vs Object
ü A Class is a blueprint for an object. Objects and classes go
hand in hand.
ü We use classes to create objects. So a class describes what an
object will be, but it isn't the object itself.
ü Classes describe the type of objects, while objects are usable
instances of classes. Each Object was built from the same set
of blueprints and therefore contains the same components
(properties and methods)
Class Diagram
Definition

6. What is Class diagram?
ü Class diagram is a graphical notation used to construct and
visualize object oriented systems. A class diagram describes
the structure of a system by showing the system's
§ classes
§ their attributes
§ operations (or methods)
§ and the relationships among objects
ü Class diagram is not only used for visualizing, describing, and
documenting different aspects of a system but also for
constructing executable code of the software application
Class Diagram
Definition

7. Use of Class diagram?
ü Describing the static view of the system
ü Showing the collaboration among the elements of the static view
ü Describing the functionalities performed by the system
ü Construction of software applications using object oriented
languages. Class diagrams are the only diagrams which can be
directly mapped with object-oriented languages and thus widely
used at the time of construction → the most popular UML
diagram in the coder community
Class Diagram
Definition

8. Elements
Class Diagram

9. Class Diagram
Elements
1. Main components of a Class 2. Relationships

10. Class Diagram
Elements
1. Vital components of a Class
1.1. Upper Section
1.2. Middle Section
1.3. Lower Section
2. Relationships

11. Class Diagram
Elements
1. Vital components of a Class
1.1. Upper Section: name of the class
ü Capitalize the initial letter of the class name
ü Place the class name in the center of the upper section
ü A class name must be written in bold format
1.2. Middle Section
1.3. Lower Section
2. Relationships

12. Class Diagram
Elements
1. Vital components of a Class
1.1. Upper Section
1.2. Middle Section: class attributes, with following characteristics:
ü A meaningful name assigned to the attribute, explain its usage
ü The accessibility of an attribute class is illustrated by the visibility factors
ü The attributes are written along with its visibility factors, which are:
public (+) | private (-) | protected (#) | and package (~)
1.3. Lower Section
2. Relationships

13. Class Diagram
Elements
1. Vital components of a Class
1.1. Upper Section
1.2. Middle Section: class attributes, with following characteristics:
1.3. Lower Section
2. Relationships

14. Class Diagram
Elements
1. Vital components of a Class
1.1. Upper Section
1.2. Middle Section
1.3. Lower Section: methods or operations. It demonstrates how a class
interacts with data. Each attribute has a type. Each operation has a signature
2. Relationships

15. Class Diagram
Elements
1. Vital components of a Class
1.1. Upper Section
1.2. Middle Section
1.3. Lower Section: Signatures (Data types)
2. Relationships

16. Class Diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association (Kết hợp)
2.2. Dependency (Phụ thuộc)
2.3. Generalization/ Inheritance (Kế thừa)
2.4. Realization (Hiện thực hóa)

17. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association (kết hợp)
ü A structural link between two peer classes
ü There is an association between Class1 and Class2
ü A solid line connecting two classes
ü It can form several types of associations: one-to-one, one-to-many, many-to-one
and many-to-many
ü Multiplicity: A multiplicity is a factor associated with an attribute. It specifies
how many instances of attributes are created when a class is initialized. If a
multiplicity is not specified, by default one is considered as a default multiplicity

18. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association - Examples

19. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association
4 types of association
ü unidirectional/ directed (một chiều)
ü bi-directional (hai chiều)
ü reflexive (phản xạ)
ü aggregation (tập hợp)
The mostly used associations are unidirectional and bi-directional.

20. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association ← Unidirectional/ directed
ü The directed association is related to the direction of flow
within association classes
ü In a directed association, the flow is directed. The
association from one class to another class flows in a single
direction only
It is denoted using a solid line with an arrowhead

21. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association ← Bi-directional
Two objects might store each other in fields

22. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association ← Reflexive
ü In a reflexive association, the instances of the
same class can be related to each other
ü Reflexive association states that a link or a
connection can be present within the objects of
the same class
ü This occurs when a class may have multiple
functions or responsibilities

23. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association ← Aggregation (has-a relationship)
ü It represents a "part of" relationship
ü Class2 is part of Class1 (collection)
ü Many instances (denoted by the *) of Class2 can be
associated with Class1
ü Objects of Class1 and Class2 have separate lifetimes

24. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.1. Association ← Aggregation ← Composition (part-of
relationship)
ü A special type of aggregation where parts are
destroyed when the whole is destroyed
ü Objects of Class2 live and die with Class1
ü Class2 cannot stand by itself

25. Class diagram
Elements
Aggregation relationship Composition relationship
Dependency In an aggregation relationship, a child can exist
independent of a parent
In a composition relationship, the child cannot
exist independent of the parent
Type of Relationship Has-a relationship Part-of relationship
Type of Association a weak association strong association
Examples A doctor has patients when the doctor gets
transfer to another hospital, the patients do not
accompany to a new workplace
A hospital and its wards. If the hospital is
destroyed, the wards also get destroyed
1. Vital components of a Class
2. Relationships
2.1. Association ← Aggregation ← Composition

26. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.2. Dependency
ü A special type of association
ü Exists between two classes if changes to the definition
of one may cause changes to the other (but not the
other way around)
ü Class1 depends on Class2

27. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.3. Generalization/ Inheritance
ü Represents an "is-a” / parent-child relationship
ü SubClass1 and SubClass2 are specializations of SuperClass
(Abstract Class)

28. Class diagram
Elements
1. Vital components of a Class
2. Relationships
2.4. Realization (hiện thực hóa)
ü One entity denotes some responsibility which is not
implemented by itself and the other entity that
implements them.
ü This relationship is mostly found in the case of interfaces

29. 1. Vital components of a Class
2. Relationships
ü Exercise: Develop mind-map diagram for
Class Diagram Relationships
Class Diagram
Elements

30. 1. Vital components of a Class
2. Relationships
Class Diagram
Elements

31. vs Use Case Diagram
Class Diagram

32. Class diagram
Use case diagram vs Class diagram

33. Use Case Diagram
Notations / Symbols
Relationships
ü Association: A line between actors and use cases represents
which actors are associated with which use cases
ü Include: defines that a use case contains the behavior
defined in another use case
ü Extend: specifies that the behavior of a use case may be
extended by the behavior of another use case
ü Generalization: represent inheritance relationship between
model elements of same type
Association Include Extend Generalization

34. Use case diagram Class diagram
What kind of? Behavioral diagram Structural diagram
What describe? Describes functional requirements Describes the structure of a system
How to describe?
By mentioning that who will perform what function and
which kind of association is exist between functions (use
cases)
By showing the system’s classes, their attributes,
functions and the relationships among objects
Supported
relationships
Association, includes, extends, Generalization Association, Dependency, Generalization, Realization
Specify Specify the behavior (what system will do?)
Specify the internal structure that will help to complete
a functionality mentioned in use cases
Representation
Use cases can be denoted both by textual (UC
description) and visual representation (UC diagram)
Only denoted by visual representation
What summarizes?
Only summarizes relationships between use cases,
actors, and system
Only summarizes relationships between classes of the
system
Order of execution
Does not show the order in which steps are performed
to achieve the goals of each use case
Does not show the order in which classes executes

35. Examples
Class Diagram

36. Class Diagram
Example 1 – Order System

37. Class Diagram
Example 2
Generalization/ Inheritance

38. Class Diagram
Example 3
ü Generalization/ Inheritance
ü Realization

39. Class Diagram
Example 4 - Package

40. Practice
Class Diagram

41. Session 13 Review
Class Diagram

42. Class Diagram
Session Review
Review content
1. What is multiplicity in Class diagram?
2. What is Reflexive association in Class diagram?
3. Aggregation relationship vs Composition relationship?
4. Use Case diagram vs Class diagram?
5. Mind-map diagram: develop a mind-map diagram to present all of Class diagram relationships types