The DBMS data source must provide an accurate mapping between the CODASYL model which DBMS implements and the relational model that client/server tools use. An accurate mapping allows you to use a relational-based tool without losing any of the CODASYL functionality. This section describes the mapping implemented by the DBMS data source and illustrates how to implement common DBMS data access operations using SQL.

The DBMS data source adds one or more virtual columns to every DBMS table in order to implement the CODASYL-RDBMS mapping. These columns, referred to as Virtual Columns, appear like any other column to the client application, even though they are not physically part of the database. The data source driver makes special use of these columns in both read and write operations.