Re: database design method

On 8 Nov 2002 22:22:30 +0100, hidders_at_hcoss.uia.ac.be (Jan Hidders) wrote:

>Not all imperative extensions make it computationally complete.

I thougth you only need a if-then and while-do instructions.

>even if you add enough to simulate a Turing machine, you still could be
>computationally incomplete.

Sure?

I always heard that a Turing machine is an example of computationally complete "language".

And a quick google search points to that.

http://www-2.cs.cmu.edu/afs/cs.cmu.edu/academic/class/15451-s01/lectures/lect22/NP-complete.pdf

> 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?

Not, but Date says that it will never feasible to procure a declarative syntax for all possible referential actions.

"An Introduction to Database Systems" Chapter 8.8

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

var R2 virtual relation TClose R1;

Alfredo Received on Sat Nov 09 2002 - 13:39:43 CET