Cardinality issue in IDT

[Former Member]

Hello Friends,

I need your help in two aspects of cardinality in the SAP Information Design Tool.

1. Suppose if the SAP Information Design Tool is detecting N:N cardinality but if I set it N:1 cardinality manually. Will I face any data issues in the webi reports?

2. If I didn't set any cardinality, I just joined the universe tables and exported to the repository without setting the cardinality.Will I face any data issues in the webi reports?

Can you please answer my above questions quickly.

Thanks in advance.

Regards,

Bhaskar Reddy P.

[former_member207878 · Accepted solution]

Hi Bhaskar,

If my reply solved your problem, then request you to close this thread by marking it as answered.

Cheers

Sahil

[former_member207878]

Its not mandatory to define cardinalities between two tables but is a Best practice to do so.

If you set the cardinalities, in the integrity check, BO tool will allow to show you join divergence or possible Traps in your structure and also it helps for any third person to see and understand the relationship.

If you don't set it, it is not going to impact in anything as the sql generated is not dependent on cardinalities which are set in Universe structure and will give you output as expected.

Cheers

Sahil

[Former Member]

Hi Sahil,

Thank you.

It's cleared.

[former_member207878]

Hi Bhaskar,

Please find my response below for your questions:

1. Suppose if the SAP Information Design Tool is detecting N:N cardinality but if I set it N:1 cardinality manually. Will I face any data issues in the webi reports?

Sahil: By default what BO does is, It takes some chunk of data and detect cardinality according to that data. which is not always 100% correct. So if you know that cardinality should be N:1 instead of N:N, then you can set it manually. Then you will get expected output.

2. If I didn't set any cardinality, I just joined the universe tables and exported to the repository without setting the cardinality. Will I face any data issues in the webi reports?

Sahil : We set the cardinalities, just to check that we don't have any Fan/Chasm trap, If you don't set it then IDT will not be able to judge that there is any traps exist in your universe design or not. so you may get wrong data.

Cheers,

Sahil

[Former Member]

Hi Sahil,

Thank you for the reply.

1. Which means I can change the cardinality manually (Example: N:1) even though IDT is detecting one carnality (Example: N:N). You are saying that there will no data issues after setting the cardinality manually?

2. How the cardinality is related to traps (Chasm/Fan). Can you please make me understand in detail.

Thank you in advance.

Regards,

Bhaskar

[former_member207878]

Bhaskar,

To answer your first point, If you have analysed data at backend and you are sure that cardinality is N:1 instead of N:N then go ahead with N:1. As I said in earlier response. IDT doesn't detect cardinality 100% true.

And for your second point, If you are aware of Join path problem then it is easy for you to understand.

A one to many join links a table, which is in turn linked by a one to many join. This type of fanning out of one to many joins can lead to a join path problem called a fan trap. The fanning out effect of “one to many” joins can cause incorrect results to be returned when a query includes objects based on both tables.

                        Table 1( 1 )   -> table 2 ( N ) -> Table  3( N )

It means, it is necessary to define cardinality for IDT to detect traps/loops. Otherwise IDT will not able to understand that 2 tables has which type of join, so it will not able to tell you that your universe design is having any type of trap or not.

Cheers

Sahil

[Former Member]

Hi Sahil,

I am clear about the 1st point.

I need clarity on the second point:

Let's say if I don't have snow flake schema in my universe which means I have star schema (A fact table surrounding by a dimension tables) and also let's say I don't have any traps (Chasm/Fan) in my universe. In that case..Can I go ahead without setting the cardinalities? I mean to say should I get the proper data/output in the webi reports even though I didn't set the cardinalities in the universe?

Please clarify this point. Thank you so much for your quick response.

Regards,

Bhaskar