The use case diagram of include and extend
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I remember when I first learned UML last year, I wrote a blog on use case diagrams - UML Diagram - Use Case Diagram。
The afternoon questions of the May 2011 soft test, the test to the use case diagram, suddenly feel some ambiguity about the concept of include and extend in the use case diagram, so move out, with everyone to learn.
In fact, after careful consideration, the two concepts are still very well understood, as the name implies, include is the meaning of "contain", extend is the meaning of "extend".
Although include means to include, I believe that include in the use case diagram, mainly reflects the idea of "abstraction". That is, when two or more use cases have the same parts, the set of actions can be abstracted out as a separate sub-use case in which the common parts are abstracted.
Because the sub use case is abstracted, neither it nor the base use case is a complete use case; only when they are combined is it a complete use case.
We often design a query screen like this when we are working on a system.