What is the chasm and fan traps in Business Objects

Chasm trap The Chasm trap occurs when two many to one joins converge on a single table. For example a customer can place many orders/and or place many loans. Fan trap The Fan trap occurs when a one to many join links a table which is in turn linked by another one to many join. For example when you run a query that asks for the total orders by each order line, for a particular customer, an incorrect result is returned as you are performing an aggregate function on the table at the one end of the join, while still joining to the many end

It is common Universe problem when you start to built schema to the scratch. Loops & Traps.

Loop: it is the close join path circle where you cant out with resolving the loop. In this case you would have less data to retrieve b/c of extra condition make your loop. mean(Actual n=n-1) and In the loop Number of Table = Number of Join. Two way to resolve the loop 1- Alias 2-Context.
check integrity check On Universe and find out the loop.
Fan Traps: Occurs when "one to many" join Fan out to another to "one to many" Joint fan out to another table.

Chasm Traps: Occurs when Three tables are join with "many to one" relationship and there is no context available to resolve the Traps. when you have a traps in your schema you will have more record coming (Cartesian Product).

cheers.