Star schema on an FM model based on relational data

[huhumix]

Hi,

I want to leverage the dynamic cubes ( cognos version 10.2.2) , but for this I would need to have the data as star schema.

I have the data in DB2 and it's a relational database. The FM model is build on that data  and it's as compatible query mode.

My question is : can i build a star schema in the current FM ( or a new one from that matter) in the database view,  if my database is relational ? Or do I need the database/datawharehouse to be as a star schema from the start ?

Hope i made sense :)

[saumil287]

Hi,

It is not necessary that your database should be a star schema.
If your database is not in the form of star schema , then you should model your tables in a way to create a star schema.(eg gosales sample) that is not in the form of star schema but through modelling in Frame work mgr , They created a star schema for each fact tables in gosales sample.
For that u need to analyse tables that are dim, facts and so on and then do the modelling. As far as your reporting needs is concenred. It is not mandatory to have a star schema.




Regards
saumil sanghvi

[huhumix]

Thanks,

Ok. So i can build a start schema by modeling in my FM , even if the underlying database is a relational one ( not star schema).

Do you know if there is a big query performance difference between having a star schema modeled in the FM on a DB which is not a star schema  vs having from the start the database as a star schema ?

Thanks@

[saumil287]

Hi,
So i can build a start schema by modeling in my FM , even if the underlying database is a relational one ( not star schema). -YES

Once the model is in the form of star schema, It guarantees that it will not give any wrong results, performance will also be increased.
but it is based on the reporting needs, It is not mandatory that you should have a star schema. if your reporting needs are completed without achiving star schema, Then no issue.
But IBM best practices say that its good if the model is created as star schems.

Pls go through IBM doc so that you can get better understanding.

Thanks

[MFGF]

Hi,

I want to leverage the dynamic cubes ( cognos version 10.2.2) , but for this I would need to have the data as star schema.

I have the data in DB2 and it's a relational database. The FM model is build on that data  and it's as compatible query mode.

My question is : can i build a star schema in the current FM ( or a new one from that matter) in the database view,  if my database is relational ? Or do I need the database/datawharehouse to be as a star schema from the start ?

Hope i made sense :)

Hi,

If you are creating Dynamic Cubes, then IBM strongly recommend your data is physically stored in star/snowflake schemas, yes. The replies below seem to be pertinent to modelling DMR in Framework Manager (ie you create objects in FM that look like star schemas) but for Cube Designer this is not the case.

You could probably get a Dynamic Cube to build using non star/snowflake schema tables, but you might not get the performance you desire or the appropriate aggregates recommended.

MF.

[maxchuie]

Did you find when you used FWM as the source and you imported the model it does not carry the relationships?

[bus_pass_man]

When you import an FM model into Cube Designer as cubes and dimensions the relationships are transformed into their analogues if they can be transformed.  This means column mappings will work although edge cases might not fully generate.  Relationships which are expressions are non-starters.

I direct you to chapter 16 in the new Cognos Dynamic Cube redbook.
http://www.redbooks.ibm.com/redpieces/abstracts/sg248064.html?Open

The online help is here:
http://www-01.ibm.com/support/knowledgecenter/SSEP7J_10.2.2/com.ibm.swg.ba.cognos.ug_cog_rlp.10.2.2.doc/t_cog_rlp_migrate_fm_package.html