Re: MV Keys
Date: Wed, 8 Mar 2006 12:40:26 +0100
Message-ID: <MPG.1e78e10023e33f6098979a_at_news.ntnu.no>
In article <WjyPf.43786$Jd.38191_at_newssvr25.news.prodigy.net>,
brian_at_selzer-software.com says...
> > I disagree. A value in itself is not a fact. In the context of the RM,
> > only tuples in relations are facts. The cartesian point (2,3) is not a
> > fact; the numbers 2 and 3 don't become more associated with each other
> > just because I refer to this point. Only when it is put into a relation
> > can it become (part of) a fact, e.g. "A FooBar is located at (2,3)".
> >
> You're right. A value in itself is not a fact. Perhaps I should be a
> little more precise. A composite value is a sentence which, once stated in
> a database, becomes a fact. "x is 2" is a sentence; "y is 3" is a sentence.
> "x is 2 and y is 3" is also a sentence. The juxtaposition of 2 and 3 in the
> ordered pair representing a cartesian point is a sentence. Furthermore, in
> the RM, attribute values are facts, not just tuples, because all stated
> values in the RM are named.
I disagree that names have much to do with it.
> Thus a tuple in a relation R{A, B, C} is the
> set of propositions {A has value 3, B has value 7, C has value 2}.
Of course, this is by some definition (a common one, I believe---but
perhaps not universally accepted?), so you could claim that your
definition is better---but I don't think it is. For one thing, it runs
into trouble the moment you introduce more tuples: If one tuple means
(among other things) that "A has value 3" is a fact, and another claims
that "A has value 5" is a fact, don't they contradict each other?
> The
No, a tuple by itself is not a fact either. Only within the context of a
relation does it make sense to talk about facts.
> The problem is that the widgit list domain is a set of lists of widgits,
I'm not able to make much sense of that, and I'm still not completely
clear on what combinatorial rules are. Can you make a concrete example
of widgit lists that shows the problems you imagine?
> tuple itself also has a truth value, "A has value 3 and B has value 7 and C
> has value 2." which is a proposition in conjunctive normal form.
> which can be constructed using the combinatorial rules. Some of the
> constructed lists may not violate the constraints, so the meanings overlap.
> This is not true of the use of integers in multiple places, because integers
> describe one aspect of a domain, they're not the domain.
-- JonReceived on Wed Mar 08 2006 - 12:40:26 CET