Main use of Cardinalities is to detect loops as said by one of member.

It is always advisable to manually assign cardinalities. Browse the database first figure out cardinalities and then apply the same manually. BOBJ can sometime take lot of time detect cardinalities as it traverse through individual record to figure out cardinality.

Regards


Rajnish Kaushal

Cardinality describes a join between 2 tables by stating how many rows of one
table will match with rows of another table. It is very important to detect join
problems and to create the contexts to correct the limitations of a target
table.

BO designer can automatically detect and set cardinalities for each join.
But we manually check the cardinalities based on the nature of keys that are
joined.

Drag the column of first table to the corresponding column of second table or
simply go to Insert->Join to create a join between 2 tables.

You can manually change the cardinality from n-n [many to many] or 1-n or n-1
or 1-1 and Click on "Detect". In BO It is always best to use 1-n cardinality
for fast data retrieval. Always delete the unnecessary joins which have n-n
cardinality as these joins create loops.