Fan trap and chasm trap - Database

Question

Can anyone tell me what is chasm trap? Perhaps fan trap too as I\'m not too clear. Also, please provide easy to understand examples (via Chen notations).

My understa

Answer 1

Based on Conolly&Begg:

Fan trap occur in a situation when a model represents relationship between entity types however a path between certain entity occurrences is ambiguous.

Example: (Staff)-1:N-has-1:1-(Division)-1:1-operates-1:N-(Branch) in this model it may be impossible to determine the branch a staff belongs to, in the situation when staff belong to division having more than 1 branches.

Restructuring the model resolves trap (Division)-1:1-operates-1:N-(Branch)-1:1-has-1:N-(Staff)

Chasm trap occur when a model suggests relationship between entity types however a path between certain occurrences does not exist.

Example: (Branch)-1:1-has-1:N-(Staff)-0:1-oversees-0:N-(PropertyForRent)

Because Staff relationship to PropertyForRent is with optional participation (0:1) for staff the path for Branch to PropertyForRent may not exist. Solution to this would be direct relationship between Branch and PropertyForRent with mandatory participation.