The DataServer places OpenEdge equivalents for the data definitions from an Oracle database into a schema holder. A schema holder contains only data definitions for one or more non-OpenEdge databases. When you issue ABL statements, they are compiled into calls to the Oracle database. When the OpenEdge client executes ABL statements and retrieves information from the Oracle database, it relies on data definitions maintained by the Data Dictionary in the OpenEdge schema holder.
The following figure shows the internal logic of the OpenEdge DataServer for Oracle.
Figure 2. The OpenEdge DataServer for Oracle logic
The DataServer uses the Oracle Call Interface (OCI) to access an Oracle instance. An Oracle instance provides the software mechanisms for accessing and controlling a database. When you start up the Oracle Database Manager (DBMS) against a database, you create an Oracle instance. See your Oracle documentation for more information on instances.
When you execute an OpenEdge application that accesses an Oracle database, the ABL compiler translates ABL statements in the OpenEdge application into their SQL equivalents. The DataServer then issues the SQL statements to the Oracle instance through the OCI. The Oracle instance processes the SQL statements and returns the results to the application through the OCI.
You can also send SQL statements directly to Oracle. The DataServer passes SELECT SQL statements that you reference in an ABL application directly to Oracle without translating them. The DataServer also allows you to issue PL/SQL statements from an OpenEdge application.
