Go to your database menu, database expert, current connections.
Right-click on your connection. Properties.
If it is Oracle Native it will say "Database Type: Oracle Server". If it is OLE, it will say OLE, If it is ODBC it will say ODBC.
The first being the least helpful of these, since they're all hooking up to Oracle.
Native will show a 'service', ODBC will show a 'datasource name' and a 'UseDSNProperties', Ole will show a 'provider'.