Extend represents the specification that the behavior of a UseCase may be extended by the behavior of another (usually supplementary) UseCase. The extension takes place at one or more specific ExtensionPoints defined in the extended UseCase. Note, however, that the extended UseCase is defined independently of the extending UseCase and is meaningful independently of the extending UseCase. On the other hand, the extending UseCase typically defines behavior that may not necessarily be meaningful by itself. Instead, the extending UseCase defines a set of modular behavior increments that augment an execution of the extended UseCase under specific conditions. Note that the same extending UseCase can extend more than one UseCases. Furthermore, an extending UseCase may itself be extended.<br/><br/>Semantics:<br/>An Extension relation identifies an extension UseCase which extends an extendedCase UseCase.<br/>
