4. The method of claim 1 , wherein the identifier in the physical database comprises a primary key from a column of a relational table, and wherein the identifier used to distinguish instances of the model entity comprises values stored in the primary key column of the relational table.
4. The method of claim 1 , wherein the identifier in the physical database comprises a primary key from a column of a relational table, and wherein the identifier used to distinguish instances of the model entity comprises values stored in the primary key column of the relational table. 5. The method of claim 4 , wherein the linking function comprises an SQL query configured to retrieve values stored in the primary key column of the relational table related to a primary key value input to the function.