Fan trap and chasm trap - Database

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 understanding thus far: I understand that Fan trap is M:1:1:M, which suggests the paths between entities is ambiguous.
I understand that. For example, if M represents Student and the other M represents School then it'll be ambiguous because we don't know which student studies at which school (that's what I understood so far).

However, I cannot grasp what is chasm trap.

Also, how can I identify the traps and then fix it?

Solution

In simple word, for both the cases (FAN & CHASM) it will produce more line(result sets) than actual. How to identify

FAN -> 1-N-N means table relation from one -> many -> many
CHASM -> N-1-N means one row table to two or more table many relation
LOOP -> join all tables and when make loop like circle (In this case we will lose some rows absolutely)

Nothing to identify but when you create Universe than we have to keep our eyes open, if you see out of these situation while developing Universe than there will be a problem always. So rectify by applying aliases, context.

Once all problems solved at Universe level than we are good to go for reporting. By practice you will have excellent knowledge.