The principal connection to an OBI Server inside the Oracle BI System is made through an Odbc Connection.
The BI Presentation Service and the Administration Tool use this connection method to connect and manage the BI Server : Check this article for more details
OBI Server can handle multiple repository but you can connect to only one at the same time by DSN Odbc Connection. Therefore, you must set up an ODBC connection for each repository.
In 11g, OBI is deployed in a clustered configuration by default. Because of this, the default ODBC DSN for the Oracle BI Server points to the Cluster Controller by default, rather than to the Oracle BI Server.
When you have create an Analytics ODBC Data Source, you can use it: