Is it a good practice to have cognos repoting system from the operational Database whic is totally normilized
Normally, we will not do this. Because, data will not be in transformed in operational DB.So,we cant deliver the report as BI requested.
If we don't have time for ETL. We can build reporting system on operational DB.
what about the performance of report on olpt source when compare to olap or a modeled data
This would largely depend on the type of report/queries involved. Allowing the casual user to develop their own reports against OLTP is probably the biggest no-no. Otherwise some carefully designed reports which are thoroughly tested prior to production phase may be perfectly acceptable