Various terms have been used for systems that have extended the relational data model.
The original term that was used to describe such systems was the Extended Relational
DBMS (ERDBMS). However, in recent years the more descriptive term Object-Relational
DBMS has been used to indicate that the system incorporates some notion of ‘object’,
and the term Universal Server or Universal DBMS (UDBMS) has also been used. In
this chapter we use the term Object-Relational DBMS (ORDBMS). Three of the leading
RDBMS vendors – Oracle, Microsoft, and IBM – have all extended their systems into
ORDBMSs, although the functionality provided by each is slightly different. The concept
of the ORDBMS, as a hybrid of the RDBMS and the OODBMS, is very appealing, preserving
the wealth of knowledge and experience that has been acquired with the RDBMS.
So much so, that some analysts predict the ORDBMS will have a 50% larger share of the
market than the RDBMS.