Re: deductive databases

On Wed, 11 May 2005 07:22:11 -0700, alex goldman wrote:

> yet, AFAIK the expressive power of modern state-of-art database software
> like Oracle and PostgreSQL still falls far behind first-order logic: it
> essentially doesn't have functors or recursion. Does anyone know why?

I believe that Nilsson's book actually describes some of the difficulties related to recursion: It's non-trivial to implement because it opens a can of worms with regard to never-ending queries, etc.

Anyhow, both IBM and Oracle have recursive SQL, and I think I've read that MSSQL 2005^6 will get it, as well. IBM's recursive SQL features are rather close to SQL:1999/SQL:2003 (the standard) while Oracle's variant is non-standard and not as powerful, as far as I know.

-- 
Greetings from Troels Arvin, Copenhagen, Denmark