Use Case Diagram

The use case diagram captures the dynamic behavior of the system. The running condition of a system can be viewed as the dynamic behavior of the system. Many use case diagrams are required for designing a system. It is not sufficient to have the static behavior of the system; dynamic behavior is much more beneficial for developing a system. Usually, these diagrams are used for retrieving the requirements that can be internal or external. Actors play an essential role in the use case diagram. The use case diagram describes a critical purpose in modeling a system.

  • Use case diagram consolidates actors, their relationship, and use cases for enveloping the functionality of the system.
  • It designs the functions, services, and tasks needed by a subsystem or system of the application.
  • It portrays the leading functionalities of the system.
  • Use case diagrams are also used to illustrate how a system can be handled.

Aim of the use case diagram

One of the most essential aims of the use case diagram is to depict the dynamic facet of the system. Use case diagram conjures use cases, persons, so many kinds of stuffs that conjure elements and actors culpable for the use case diagram implementation. It represents how an entity from an independent environment can cooperate with a piece of a system. Internal and external requirements can be accumulated through use case diagrams.

This aim should be described in the following manner:

  • Identify the actors.
  • Requirements are gathered (internal or external).
  • Get an outside view of the system
  • Find the influenced factors of the system.

Drawing of the Use Case Diagram

Functionalities must be determined after analyzing the entire system. After that, the functionalities are transformed into use cases, and these use cases will be used in these diagrams. Then the actors will be employed, which will further collaborate with the system. The actors may be a private entity or a system, and it needs to have a logical entity for the system’s functionalities for which it is going to reach-out. These actors are the things or a person that conjures the functionality of the system.

When all the use cases and actors are employed, then the relationship among these use cases and actors is investigated. It also analyzes how many times an actor disseminates to the system.

Some rules or regulations regarding use case diagram are as follows:

  • A meaningful and valid name must be nominated for the use case or actors of the system.
  • Notations should be appropriately used when needed.
  • The interactions must be produced between the actors and use cases among several interactions.
  • An actor’s conversation with the use case should be specified correctly.

Key points to draw a Use Case Diagram

Here are some essential key points which should be kept in mind while drawing a use case diagram. These are enlisted as below:

  • Simplicity
  • Completeness
  • Interaction with use case must be served
  • At least a module should be described by use case diagram
  • It must be generalized if it’s size is too large


The following diagram shows an example of the use case diagram. In this example, there are two actors, i.e., library user and librarian. The total number of use cases in this diagram is four that serve some functionalities of the library management system. Every actor cooperates with a specific use case. The diagram is shown below:

Use Case Diagram

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