Just as a port is needed for the client applications to connect to the Application Server, there must also be a method for connecting the Application Server to the back end database. The Application Server accomplishes this by creating Database Links that use Open Database Connectivity (ODBC) Data Sources to point to the different databases that might reside on the database engine. For example, the database engine may have multiple system databases: the live company database, the included sample database, a training database, etc. The Application Server provides Database Links that allow client access (through the Data Source) to each of these individual databases. Each database to which you want to provide access will have its own Database Link defined within the Application Server. Each Database Link will in turn have its own Data Source defined to link to the database.

The Application Server creates a separate Database Link for each database that resides on the database server engine. A Data Source is created for each Database Link to allow communication with the database.