In the below link IBM states the databases Cognos can work with
http://www-01.ibm.com/support/docview.wss?uid=swg27021368#db
But, we all know that Cognos also works well with XML, Excel etc which have not been mentioned in the list on the website. So, is the list in the website incomplete or is it that for everything other than those mentioned we need a ODBC connection and deosnt work well directly
The data sources listed are the the ones that are supported directly. That means that Cognos will list that type when setting up a connection, and knows how to call the driver for that data source type. The ones that are not listed directly, but are still supported are covered by other ODBC data sources.
It is important to note the the ODBC data sources must be ODBC 3.5 compliant, and this is only supported by Cognos installed on Windows.