cardinality detect error

[former_member186586]

Hi everybody.

i am working on default club database .

between reservations and reservations_line table detect cardinality says me : 1-1 relationship.

but its wrong. because reservation_lines table has many reservation number..

i fixed this manually , but what cause this fault. ??

[Former Member · Accepted solution]

Its a known issue that auto detect cardinality is not very reliable. It uses an algorithm utilizing physical record counts of the table which is likely to be incorrect at times.

So it is always advisable to use the data model to manually setup the cardinality in the universe and not rely on the detect cardinality option.

[Former Member]

From the old days of version 5 until now, the detect cardinalities functionality has always been flawed. They almost admit it by having it as separate to the "Check All" within the Integrity Check functionality!

Use the data model to determine the cardinalities.

If you've got a dimensional model (a data warehouse), then most cardinalities are straightforward:

D -< F

Make sure you set them as the detect contextsalgorithm works brilliantly and saves you wondering what belongs where.

[former_member4998]

HI..

Cardinalities describe a join between 2 tables by stating how many rows in one table will match rows in another. This is very important for detecting join problems and creating contexts to correct the limitations.

The strategy is always used when you choose to detect the joins or cardinalities in your table schema.

You should always manually check the cardinalities taking into consider the nature of Keys that are joined.

You need to verify that cardinalities are correctly set for all joins in your schema to ensure that you have the correct contexts, and that you have valid join paths to get the correct data.