Re: What is an "Extensible Database"

An "extensible DBMS" is a data manager where the "data model" (say, relational or SQL data model) is treated more as a framework than as a finished product. For example, the relational data model has logical notions of domains, relations, and relational operators. In an extensible DBMS users can 'extend' the physical implementations of each of these. For instance, they can add to the set of domains--adding a new user-defined data type and operators--relations--if you don't like page oriented disk access but still want to be able to write queries you can implement your own storage layer--and even relational operators--want one of Date's fancy temporal operators? or got a new join algorithm you want to add?. Note that this doesn't mean that an engineer working for the vendor can add these things, but rather that an "after market" in extensions can be created which "plug into" the DBMS and extend its functionality.

The marketing term most frequently associated with this idea was "Object-Relational". Early work on building this class of system was undertaken in the late 1980s. Notable extensible DBMSs today would include PostgresSQL. Most commercial SQL DBMS products today support such extensions to a greater or lesser extent. Received on Thu Dec 09 2004 - 00:28:42 CET