Extend relationship

An extend relationship between use cases means that the base use case implicitly incorporates the behavior of another use case at a location specified indirectly by the extend use case [BRJ99]. The base use case must be defined to completely stand by itself. Its description should be independent of the use case that extends it. The extend use case will be executed only when some particular circumstances will be satisfied in the base use case. Extended use cases can be successfully used to add additional functionalities to base use cases without questioning their integrity.

Let us consider as an example the process of approving extension documents (http://ers.ifas.ufl.edu) at the Institute of Food and Agricultural Sciences (IFAS), at the University of Florida. Each document needs to be peer-reviewed by at the least two reviewers, before it goes for approval to the department chair. According to this practice, most of the time the reviewers selected to review the document are sufficient. The department chair can add


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