A use case diagram defines a relationship between a users called as an actor and its different activities known as use cases, it is a simplest way of showing interaction between a user and the system.
In another word it can say that use cases are the blueprints of any system.
A use case can be draw by either using a circle or an ellipse, Because of its very simple in nature it is a very good communication tool for the stakeholders and they can easily interpret it completely and correctly.
It is used in a system to gather requirement including internal and external influences, also to analyse system functionalities and to identify the actors.
In a Use case actors can be human, external applications or any internal applications.
It is very important in a use case to give it’s a suitable name specially which can identify its functionality,name the actors too, also identify the types of relationship.
Value of Use case diagram:
By using use case diagram we can gather requirements of the system and that data can be use in different ways:
1-It helps to identify system functions and how the user interacting with them.
2-It is useful to present it to higher management and to the stakeholder in a simpler way.
3-It helps to identify internal and external factors.
Use case diagram has four objectives:
1- Actor: It’s an entity that performs a role in a system.
2- Use case: It represents user action in a system.
3-System: It is used to describe the scope of any system; it’s usually represented by a rectangle.
4-Package: It is use for grouping together many use cases.
Types of Relationship used in a use case diagram:
1-Association- It is relationship between a user and its function.
3- Use case Generalization.
4- Between the use cases include relationship.
5-Between the use cases Extend relationship.
Rules for creating a use case diagram:
1- First of all identifying an actor, it can be user, system or an organization.
For example –in a bank scenario actor can be bank customer, bank employee etc.
2-Now next step is to identify the use case, functionality of system associated with each user.
3-If the functionality of use cases are same , extract the common function and draw a separate use case you can connect it by using include relationship.
4-For similar attribute functionality can use the generalization relation.
For example – In a payment system making payment is a use case, which can be done by cash, card cheque, for all such use case we can use generalization relation.
5-For some function which are triggering optionally can use the extend relation.