Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]
Date: Sun, 10 Jul 2005 01:00:03 GMT
Message-ID: <nq_ze.1920469$Xk.663639_at_pd7tw3no>
Jan Hidders wrote:
> paul c wrote:
>
>> Jan Hidders wrote: >>...
> Splitting the update in a delete and an insert makes the situation even
> more complex. Assume a relation S that has a foreign key to the primary
> key of R. For an update to the PK of a tuple in R it is easy to see what
> it means to cascade that update to S. If you split the update in a
> delete and an insert this is not so simple because on the delete you
> would have to either (1) delete the corresponding tuples in S or (2)
> nullify their foreign keys, so if you then follow with only the insert
> you will have lost information. So, yes, there is a logical difference.
>
> -- Jan Hidders
thanks for your detailed reply. i've been pondering how to say that i don't agree without just saying so and giving no useful reasons. i don't think i have a really good way of explaining my disagreement. all i can say is that i feel that most discussions in this area are encumbered with the notions or artifacts of various computer languages, none of which i've ever felt very confident with, even after using some of them for years!
one that i used very briefly (briefly only because i needed money and nobody would pay me to use it) was Prolog. i've forgotten most of its nuances, but i still imagine (that's the right word, i think, since Prolog implementations that i knew of didn't work the way i hoped they would) that i would insert by simply stating a proposition, not by invoking a verb. and the statement would remain persistent even if my program ended, assuming the result of my program was 'true' in the sense that it contained no contradictions within itself (of course, it could contradict the state of the db before as they were before it was invoked), until somebody negated it. (so far, my ideal language has propositions and some negation symbol or other! also, until recent years when memory has become much more plentiful, my ideal programs couldn't have been implemented since they would depend on complete evaluation before any persistent physical 'updates' were made.)
i realize that i've brought other issues into this, but that's the gist of my argument - that when we remove, at least as much as we are able, the connotations of programming languages, indeed all language outside of propositions if that's possible, there is no difference.
maybe i'm saying something very trivial, but there seems to be something under my finger even if i can't put the digit on it.
p Received on Sun Jul 10 2005 - 03:00:03 CEST