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Relationships in Use Case diagram

A Usecase diagram is a high level diagram and will not show many details, but will communicate ideas to understand the system in basic way.

There are different elements in usecase namely,
• Actors
• System
• Usecase
• Relationship

In this blog, we are going to discuss about “ Relationship “.
Relationship is most important part of UML diagrams. It defines the functionality of an application and how each elements are associated.

Relationships are of below categories,
• Associations
• Generalizations
• Include
• Exclude

Association relationships : This is a relationship between two classifiers ( Classes and Usecases), which explains the rules and reasons for relationships.

Notation : A straight solid line between two objects.

Generalization Relationships : This is a relationship in which one child element is based on the parent element.
Generalization is of two types : – Actor generalization and usecase generalization.

Notation : A solid arrow heading towards dependency.

Example : If ‘A’ is a superclass and ‘B’ , ‘C’ are subclasses of superclass. The subclasses ‘B’ and ‘C’ are derived from superclass ‘A’, means features of ‘B’ and ‘C’ are also part of superclass ‘A’.

Include Relationships : This is a relationship in which the base usecase includes the functionality of another usecase which is mandatory. This relationship supports the reuse of functionality in usecase model.

Notation : An arrow heading towards dependency.

Example : If ‘A’ is the base usecase and ‘B’ is the included usecase. ‘B’ will be called multiple times during the execution of ‘A’. So in other terms ‘A’ cannot produce output with running ‘B’.

Extend Relationship : This is a relationship to specify that usecase extends the behavior of another usecase.

Notation : An arrow heading towards dependency.

Example : If ‘A’ is the base usecase and ‘B’ is the extend function of ‘A’. So ‘B’ may or may not be executed (optional based on certain condition). So in this case ‘A’ can still produce output without running ‘B’.

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