Re: The Foundation of OO (XDb)

"Clifford Heath" <cjh_nospam_at_managesoft.com> wrote in message news:3D0D4101.96AF363_at_managesoft.com...
> 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.

Doing so only confuses logical and physical. The logical model does not care how the dbms physically represents the data. A video is a video. AVI, MPEG and QuickTime are all just representations of Video.

> 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.

Specialization of what? Why do you think views fail to support it?

> 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.

Foreign key constraints are quite simple. If your constraints are complex, I suggest you need to reconsider your data model. If it turns out that the application domain is just complex, the complexity may be inherent in the problem.

> --
> Clifford Heath
Received on Mon Jun 17 2002 - 08:08:25 CEST