UML

Use case relationships model the dependencies between use cases in the interaction model of the system. Although, independent use cases can adequately represent simpler systems. However, in order to represent complex or large systems, we may need to construct complex use cases with the help of dependencies between use cases. Establishing relationships between use cases allows reuse of those use cases that need to be defined over and over again, which reduces developer effort.

Multiplicity in class diagram should be indicated at each end of the association. This specifies the minimum and maximum number of instances that can be linked. For example, a car has 3 or 4 wheels, but each wheel belongs to exactly one car. Place multiplicity notations near the ends of an association. These symbols indicate the number of instances of one class linked to one instance of the other class.

There are six main types of relationships between classes: inheritance , realization / implementation , composition , aggregation , association, and dependency .

A use case diagram is a Unified Modeling Language (UML) diagram for requirements elicitation. Use case diagrams provide a graphical overview of the goals (modeled by use cases) that users (represented by actors) want to achieve by using the system. Use cases in a use case diagram can be organized and arranged according to their relevance, level of abstraction, and impact on the user. They can be linked to show their dependencies, include, extend, generation relationships.