Re: object algebra

"Neo" <neo55592_at_hotmail.com> wrote in message news:4b45d3ad.0402201644.429ee9b6_at_posting.google.com...
> On the plus side, the rules make some
> representations/operations easier and more robust (ie those where data
> fits neatly in tables).

This is entirely wrong - it's where your data can be mapped to logical predicates. And if you can't do that, there's precious little you can do.

> On the minus side, the rules make other
> representations/operations more difficult (ie trees).

Trees aren't difficult in relational - not even in SQL.

> The deficiencies
> of RDM to manage things for some range of applications is why there
> are OODBs, XML, MV and XDb.

Not really:
- OODBs exist because OO was sexy
- XML exists because people forgot the past and allowed text publishers to influence data management
- MV is a holdout from the pre-relational days - TDM is... not sure what. Another XML / MV hybrid? Are there any decent explantations of it?

> XDb is a partial/experimental
> implementation of TDM. TDM is a more general model than RDM.

Unlikely. It sounds more specific.

> This is why it can equally manage things arranged as either tables or
trees,
> has OO characteristics, no NULLs, transitive closure and fits on a
> floppy to boot :)

Relational doesn't have nulls either. Codd perhaps disagreed, but the problems with nulls are well-known, and the relational community eschews them.

• erk