http://publib.boulder.ibm.com/iseries/v5r2/ic2924/index.htm?info/rzaik/rzaik678.htm

The iSeries Access ODBC driver has many connection string keywords that can be used to change the behavior of the ODBC connection. These same keywords and their values are also stored when an ODBC data source is setup. When an ODBC application makes a connection, any keywords specified in the connection string override the values specified in the ODBC data source.