On a buzzword "extensibility"-what we have learned from the ORIENT project?

To meet the ever challenging requirements of today's applications, both database research and industry are engaged in adding new features to database management systems (DBMSs). As a major effort in this direction, object-relational DBMSs (ORDBMSs) are becoming more and more popular due to their extensibility, i.e., allowing user-defined facilities to be used in the same way as built-in ones. Inspired by this idea, we started to develop a prototype ORIENT to enhance DBMSs with complex relationship semantics that are versatile in the real world but still insufficiently supported by new database technology. Our work reveals that data model changes to accommodate relationship semantics imply extensions at the processing level which are, however, not feasible in "extensible" ORDBMSs. Proper integration of new processing capabilities calls for a more open approach to database extensibility than current ORDBMSs exhibit.