How to differentiate include and extend in the use case diagram?

During requirement analysis, complex requirements always make it difficult to find out the relationship before the use case. The generalize relationship is easier to find out, and the most confusing is include and extend. Many people on the Internet do not understand this, or even make mistakes. This article tells you how to determine whether to use include or extend?

After reading it, you will understand. This figure is drawn Using Visio, so uses actually represents include (Microsoft always does not obey the standard ).

1. "include" indicates the relationship between two use cases, that is, include. to execute a use case, you must use and execute another use case. For example, if you want to "make an appointment", you need to "verify the id ". "Verification ID" is required for "borrowing books ".

2. Extend means expansion. A fine (Book expiration) may be paid when a "book return", but not all "return" will be "paid ". After certain expansion conditions are met (expired), another use case is executed.

It can be seen that the use cases of include are mostly the common parts extracted from several use cases. Extend is used to execute other use cases when it meets certain extend points.

Welcome to the discussion!