A DBMS is an Object-Relational Database System (ORDBMS), if it supports both the object-oriented data model and the relational database model, and the DBMS implements the DBMS services and components.
In order to be a true ORDBMS. the two data models must inter-operate, e.g.by allowing the values in the relational model to be object references.
A large part of the commercial field has used the Relational DBMS.
The relational area has been useful, because of the simplicity, the query language.
and the well understood underlying mathematical theories. (Commercial firms like Oracle, Sybase and Informix have a large market in this area).
A new challenge has emerged for the relational system with the arrival of client server solutions and internet solutions. The presentation part of the systems has evolved to be implemented in object-oriented languages and from there the interest for object-relational DBMS has evolved.
There has been a great interest in using object-oriented design and programming. The underlying model of object-oriented DBMS lacks the mathematical foundation that is known from the underlying model in the Relational DBMS. Without the relational algebra the object-oriented DBMS is not as well understood as the Relational DBMS.
