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Use-Case Model

The Use-case model is defined as a model which is used to show how users interact with the system in order to solve a problem.

Use case model defines the user's objective

1. interactions between the system and the user

2. and the system's behavior required to meet these objectives.

Various model elements are contained in use-case model, such as actors, use cases, and the association between them.

We use a use-case diagram to graphically portray a subset of the model in order to make the communication simpler.

Components of Basic Model

There are various components of the basic model:

1. Actor
2. Use Case
3. Associations

Actor

Usually, actors are people involved with the system defined on the basis of their roles. An actor can be anything such as human or another external system.

Use Case

The use case defines how actors use a system to accomplish a specific objective. The use cases are generally introduced by the user to meet the objectives of the activities and variants involved in the achievement of the goal.

Associations

Associations are another component of the basic model. It is used to define the associations among actors and use cases they contribute in. This association is called communicates-association.

Advanced Model Components

There are various components of the advanced model:

1. Subject
2. Use-Case Package
3. Generalizations
4. Dependencies

Subject

The subject component is used to represent the boundary of the system of interest.

Use-Case Package

We use the model component in order to structure the use case model to make simpler the analysis, planning, navigation, and communication. Suppose there are various actors or use cases. In that case, we can also use use-case packages in order to further structure the use-case model in much the similar way we use directories or folders to organize the information on our hard-disk.

Generalizations

Generalizations mean the association between the actors in order to help re-use of common properties.

Dependencies

In UML, various types of dependencies are defined between use cases.

How to Draw a Use-Case Diagram?

Use-Case

if we want to draw a use case diagram in UML first, we must study the complete system appropriately. We need to find out every function which is offered by the system. When we find out all the system's functionalities then we convert these functionalities into a number of use cases, and we use these use-cases in the use case diagram.

Actor

A use case means essential functionality of any working system. When we organize the use cases, then next we need to enlist the numerous actors or things that will collaborate with the system. These actors are used to implement the functionality of a system. Actors can be someone or something. It can likewise be a private system's entity. The actors should be pertinent to the functionality or a system in which the actors are interacting.

Associations

When we enlist the use cases and actors, then next, we need to find the relationship of a specific actor with the system or a use case. An actor should find the total number of ways in order to cooperate with the system. One actor can interact with the numerous use cases simultaneously, or it may interact with the multiple-use cases concurrently.

Using use-case diagrams, we can detect the pre-and post-conditions after communication with the actor. We can determine these conditions using several test cases.

Generally, the use-cases diagram is used for:

• Examining the system's requirements.
• Capturing the system's Functionalities.
• We use use-case diagram in order to modeling the general idea behind the system.
• System's Forward and reverse engineering using several test cases.
• Complex visual designing of software.

Basic Use-Case Diagram Symbols and Notations

System

With the help of the rectangle, we can draw the boundaries of the system, which includes use-cases. We need to put the actors outside the system's boundaries.

Use-Case

With the help of the Ovals, we can draw the use-cases. With the verb we have to label the ovals in order to represent the functions of the system.

Actors

Actors mean the system's users. If one system is the actor of the other system, then with the actor stereotype, we have to tag the actor system.

Relationships

With the simple line we can represent relationships between an actor and use cases. For relationships between use-case, we use arrows which are labeled either "extends" or "uses". The "extends" relationship shows the alternative options under the specific use case. The "uses" relationship shows that single use-case is required to accomplish a job.

Use-Case Examples

Use-Case Example-Association Link

In this use-case diagram, we show a group of use cases for a system which means the relationship among the use-cases and the actor.

Use-Case Example-Include Relationship

In order to add additional functionality that is not specified in the base use-case, we use to include relationship. We use it to comprise the general behavior from an included use case into a base case so that we can support the reuse general behavior.

Use-Case Example-Extend Relationship

With the help of the extend relationship, we can show the system behavior or optional functionality. We use <<extend>> relationship in order to comprise optional behavior from an extending use-case in an extended use-case. For example, the below diagram of the use-case displays an extend connector and an extension point "Search".

Use-Case Example-Generalization Relationship

In the generalization relationship, the child use-case can inherit the meaning and behavior of the parent use-case. The child use-case is able to override and adds the parent's behavior. The below diagram is an example of generalization relationship in which two generalization connector is connected among three use-cases.

Use-Case Diagram-Vehicle Sales Systems

The below diagram displays an instance of a use-case diagram for a vehicle system. As we can also see, a system as much as one vehicle sales system contains not in excess of 10 use-cases, and it is the delicacy of use-case modeling.

The use of include and extend is also displayed by the use-case model. In addition, there are associations that link between the use-case and actors.

Use-Case Diagram-Student Management System

The below figure shows the working of the student management system:

In the above use-case diagram of the student management system, we have two actors and five use-cases. The name of the actors is Student and Teacher. The use-cases represent the definite functionality of the student management system. Every actor interacts with a specific use-case. The student actor is able to check the test marks, time-table and attendance. These are only 3 interactions that can be performed by the student actor; however various use-cases are also remaining in the system.

It is not must that every actor has to interact with each and every use-case, but it can happen.

In the diagram, the name of the second actor is a Teacher. Teacher is an actor that is able to interact with all the system's functionalities. The teacher actor is also able to update the student's marks as well as attendance. Theses interactions of student as well as teacher actors together summarize the whole student management application.