Re: The Foundation of OO (XDb)

Bob Badour wrote:
> Someone in the creative department querying the dbms might watch a Video in
> its QuickTime representation on their Mac. Someone it the engineering
> department querying the same dbms might watch the same Video in its MPEG
> representation on their unix workstation. Someone else might watch it as an
> AVI in Excel.

> Doesn't it just make you drool? It makes me drool! Wouldn't you like to work
> with a product like that? I know I do!

Good stuff Bob, but the system you're describing already exists - Postgres. Some other DBMSs also support addition of user-written representation converters - though they "appear" to be type converters. Realistically I think that the correct way to think of this is as "conversion between subtypes", which again raises the notion of type inheritance.

Anyhow, converting video formats is just an extension of converting, say, integer formats, which all existing RDBMSs can do. The conversions might be lossy in both cases.

My complaint with RDBMSs (and the reason I have sympathy for James' system, despite his erratic evangelism) is that my data models often need to support specialisation, and though it doesn't break the relational model at all, the products don't support it natively. One must use joined tables to add extra columns to the tuples to be specialised, or sometimes, for performance reasons, nullable attributes (shudder). Full support for specialisation would introduce a vast field of implementation complexity in the constraints, for which there might need to be some new theoretical modelling.

--
Clifford Heath