Introduction of Class Diagram

The class diagram provides an analysis of the software system and displaying attributes, classes, their relationship, and operations. UML class diagram consists of operations, class name, and attributes in isolate designated compartments. It describes the kinds of objects that are within the system. Various kinds of relationships endure between them and provide a high-level designation of application. This technique can execute all types of object-oriented methods. Another class can refer by a class. A class can acquire its objects from another class. For software application advancement, these diagrams construct a code for it.

Characterization of a collection of objects with similar appearance within a system which dwells of:

Structural Features:

  • Describes what the objects of a class “know”
  • Depicts the affirm of the object of a class
  • Summary of the static or structural features of the class

Behavioral Features:

  • Describe what the objects of a class “can do”
  • Describe the manner in which the objects may collaborate or interact
  • Behavioral features are a summary of dynamic features of the class

Class Diagram Benefits

  • The class diagram clarifies data models for a highly complicated information system.
  • It gives an examination of how an application is designed before considering the real code. A class diagram can curtail maintenance time.
  • A class diagram encourages for enhancing the understanding of simplification of the application.
  • These diagrams allow detailed charts, which features the code needed to be programmed.
  • This diagram is suitable for stakeholders and developers.

Components of UML Diagram

UML diagram specifies its components in a well-defined sequence. This sequence is displaying in the following diagram:

  • Class-Name
  • Attributes
  • Operations
UML Class Diagram

Class-Name: In the UML class diagram, class-name is required to be drawn only in the representation of a class graphically. It represents in the first compartment. It is a blueprint of the object that can contribute the attributes, relationships, semantics, and operations. A class is delivered as the rectangle, including attributes, operations, and its name in isolate compartments.

Some rules must be followed while displaying a class:

  • The first character of the class must begin with the capital letter.
  • Class-Name must be represented in the middle position of the compartment.
  • It must be represented in a bold format.
  • The name of an abstract class must be represented in an italics format.

 Attributes: Attributes are represented in the second compartment just after specifying the name of the class in the first compartment. It is the named equity of the class that defines the modeled objects. A derived attribute can figure out from another attribute. For example, the age of any person can figure out easily from his date of birth.

UML Class Diagram

Characteristics of Attributes:

  • An attribute is generally written with a visibility aspect.
  • Public, protected, package, and private are the visibilities that can be represented through +, -, #, or ~ symbols, respectively.
  • These visibilities portray the accessibility of the class attributes.
  • Attributes must contain a consequential name that depicts the application of it within a class.


UML Class diagram mainly uses three different types of relationships:

  • Dependency
  • Generalization
  • Association


Dependency describes the relationship between more than two classes, in which it illustrates that the change in one class may violate changes in other classes. It depicts that one class has a dependency on the other classes. It will always found a weaker relationship between classes.

For example, an employee is dependent on an organization.

UML Class Diagram


Generalization relationships are widely used to define the concept of inheritance. A generalization provides a connection between the superclass and its subclass. A subclass inherits various properties and features from its superclass. This diagram allows for acquiring properties from one or more superclasses.

For example, Class B and Class C have their parent class A.

UML Class Diagram


The association relationship illustrates a static relationship between two or more classes.

For example, an employee is associated with an organization.

UML Class Diagram

Association Relationship Rules

Association is a verb expression or a verb or a noun expression or noun.

Association relationship must be named for displaying the role performed through the class. It is joined at the edge of the association path.


Multiplicity is the factor correlated with the attribute. It defines how many attributes instances can be created if any class is implemented. Default multiplicity can be considered as one.

For example, a company can have so many workers in their company.

UML Class Diagram


Aggregation is a subdivision and a particular version of association. It designs a relationship that is named as whole-part, among aggregate.

For example, the organization is composed of various employees. Here, the organization will go on even if employees are not available.

UML Class Diagram


It is also a unique kind of aggregation. It defines a strong relationship between two or more classes if a class is the separation of other class.

For example, an organization consists of so many employees. The organization can have many employees, where each employee belongs to one organization. So, if an organization is not working, then all the employees also removed.

UML Class Diagram

Abstract Class

The abstract class keeps a kind of operation prototype. An abstract class without operation can also be possible that is resided inside of this class. It can be used to search for some functionality around the classes. The main difference between the notation of a simple class and an abstract class is that the class name will be written in an italics format. Abstract classes do not require implementation for the provided function. It can be a best practice for the usage of abstract classes attached to one or more objects. It is neither instantiated nor initialized.

For example, a class is known as a movement that includes the method defined inside of the class. The method is named as action(). Now, action() can be achieved through any object like bus, train, dog, etc.

UML Class Diagram


These diagrams help to create a static view for an application. Object-oriented languages can be easily mapped with class diagrams. Also, it provides support for construction. These diagrams are very popular and usable among all the other diagrams. Following are some key points:

  • Primary responsibilities can properly be mentioned through the class diagram.
  • It can be widely used for a static representation of a system.
  • It provides a base for deployment and component diagrams.
  • It also assimilates reverse engineering and forward engineering.

Steps to draw class diagrams

It is most widely used to build a software application. It is not only used for the static representation of a system but also to describe various aspects of the application. A group of these diagrams can be used to represent the entire system.

Following are some essential factor to draw a class diagram:

  • It is necessary to give a proper and meaningful name for the class diagram to define an aspect of a system.
  • The responsibilities are also determined for all the classes.
  • A maximum number of undesired properties will cause a complex diagram. That’s why a reduced amount of properties must be specified.
  • User notes must be specified when you require a few aspects of the diagram to be described. It should be intelligible for a software development group, at the edge of this drawing.
  • Before designing a final interpretation, the diagram must be drawn on a plain paper. Further, it must be redrawn until and unless it is prepared for the final design.

Use of Class Diagram

They define a vital aspect in terms of understanding. The class diagram identifies an essential relationship with object-oriented languages. It is a static type of diagram, which is also known as “Structural Diagram.” It can be combined as a collection of such things as interfaces, classes, associations, collaboration, etc. The class diagram can also identify the constraints which are imposed on the system. It demonstrates a vital perspective in the formulation of the deployment and component diagrams. It provides a code to represent reverse engineering and forward engineering for a system. The primary usage of class diagrams are enlisted below:

  • It describes a static perspective of a system.
  • It shows the cooperation between all the instances in a static view.
  • It defines the functionalities displayed by a system.
  • It establishes the software application with the use of object-oriented languages.


UML Class Diagram

Example of class diagram is drawn at below: Conclusion

  • These diagrams are helpful to graph the object-oriented languages, such as C++, Python, Ruby, Java, etc.
  • The application structure overview can be provided through this diagram. It will curtail the maintenance time.
  • Essential components of the class diagram-
    • Attributes
    • Class
    • Relationship
  • Class diagrams are very supportable for the software development application.

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