Re: database design method

In article <3dcad503.381118_at_newscache4.freenet.de>, Alfredo Novoa <alfredo_at_nospam_ncs.es> wrote:
>On 7 Nov 2002 10:48:42 +0100, hidders_at_REMOVE.THIS.uia.ua.ac.be (Jan
>Hidders) wrote:
>>
>>Anyway, is there a proof somewhere
>>that Tutorial-D is computationally complete?
>
>Yes, because it also has imperative extensions.

Not all imperative extensions make it computationally complete. In fact, even if you add enough to simulate a Turing machine, you still could be computationally incomplete. Moreover I thought that it was Date's position that the constraint language and the query language should be declarative. Has that principle been abandoned?

>>Ok. Can I express that relation R2 is the transitive closure of relation R1?
>
>Yes:
>
>R2 := TClose R1;

Interesting. Can I also use that to express the constraint that the relvar R2 always contains the transitive closure of R1?

• Jan Hidders