To configure an Oracle Data Source Name (DSN), you must have specified a TNS Service Name for the database in which your workspace repositories will be stored. This is the TNS Service Name you entered when you installed the repository client.
Check the file tnsnames.ora in Repository_Client_HOME to make sure the TNS Service Name exists. The entry should look like this, where RMWPROD is the TNS Service Name:
RMWPROD (DESCRIPTION= (ADDRESS_LIST= (ADDRESS=(PROTOCOL=TCP)(HOST=tiger)(PORT=1521)) ) (CONNECT_DATA= (SID=lnx) ) )
You will also need to obtain a database user ID and password from your DBA to configure the Oracle DSN.