UML Use case diagram

A use case diagram is a diagram that describes the functions of a system by actors, use cases, and relationships.

Participant: A person who directs a system, or a system-related thing or system.

A simple understanding of use cases is the collection of functions that the system has

Relationship: Is the relationship between participants, between use cases, between actors and use cases.

The following diagram shows the relationships and symbols in the use case diagram:

Icon:

1, association relationship

2, including relationship

3, extended

4, generalization

The summary of the arrows in the graph: the generalization relationship is similar to the inheritance of classes in Java, that is, the hollow arrows in the diagram are small in scope, large in function, and at the root.   The extension is similar to generalization, pointing to a large range. The inclusion relationship is small in scope from a large range of points.

Related relations, some have arrows, some do not have arrows, arrows pointing is not sure, of course, the meaning of the expression is not the same. When the arrow points from the participant to the use case, it indicates what the participant can do. When the arrow points to the participant, it is equivalent to the system giving the participant an output data.

Use case diagram Summary diagram