Usage is a concept in Class Diagrams that represents a relationship between elements, indicating that one element (the client) uses or depends on another element (the supplier) without specifying the nature of the relationship in detail. The Usage relationship is a type of dependency that implies that the client element requires the presence of the supplier element to perform its function, but does not imply any kind of ownership or control over the supplier.
In a Class Diagram, Usage can be applied to various elements such as classes, interfaces, components, or packages. It helps to model the dependencies and connections between elements in the system, highlighting how different elements are related and rely on each other.
Example: In a Class Diagram for a system that manages a library, you might have a class called “LibrarySystem” that uses another class called “Book”. The Usage relationship between these classes indicates that the “LibrarySystem” class depends on the “Book” class to perform its functions, such as managing book loans and returns. This relationship shows that the “LibrarySystem” requires the presence of the “Book” class, but it does not imply any ownership or control over the “Book” class by the “LibrarySystem”.