Unified Modeling Language Reference Manual, The, Second Edition

extend

A relationship from an extension use case to a base (extended) use case, specifying how the behavior defined for the extension use case can be inserted into the behavior defined for the base use case. The extension use case incrementally modifies the base use case in a modular way.

See also extension point, include, use case, use case generalization.

Semantics

The extend relationship connects an extension use case to a base use case (Figure 14-133). The extension use case in this relationship is not necessarily a separate instantiable classifier. Instead, it consists of one or more segments that describe additional behavior sequences that incrementally modify the behavior of the base use case. Each segment in an extension use case may ...