Fan Trap (扇形陷阱)
When an entity has more than one 1:N relationships, it is very easy to generate a "fan trap" among associated entities. The "1" entity is the center of the "fan", and the "N" entities are the leaves of the "fan".
The leaf entities usually cannot connect each other correctly, because of the many-to-many relationships they may have between each other.
For example, the correspondence between a student and a course would be confusing - it's hard to say which student belongs to each course.
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The fan trap may exist when there are multiple one-to-many relationships fan out from the same central entity.
See more:
https://documentation.sisense.com/chasm-and-fan-traps/
Chasm Trap (断层陷阱)
When the underlying logic of the conceptual model implies a correspondence between two entities does exist but there is no pathway between them, a chasm trap may exist.
For example, a student may or may not buy a textbook, and may or may not have a course. However, textbooks must correspond with a course. How could I identify which course a textbook belongs to via the "textbooks-student-courses" relationships?
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The chasm trap may exist when there are optional participation between entities. (A student may not buy a textbook or may not enroll in a course, but a textbook must has a corresponding course and vice versa)
How could we handle fan and chasm traps? We separate confusing correspondence by adding new relationships.
