Re: The MySQL/PHP pair
Date: Fri, 05 Nov 2004 23:14:45 +0000
Message-ID: <418c0964$0$36790$ed2619ec_at_ptn-nntp-reader02.plus.net>
Dawn M. Wolthuis wrote:
>> You could say this. But then L is a "variable" (in the predicate
>> logic sense) and not a predicate. So when we translate over to
>> relations, L is atomic in the sense that the relational system
>> cannot look inside it - its inner workings are only visible to the
>> type system. This is because the relational system can only look
>> inside predicates.
>
> I don't care how it is implemented. As far as I'm concerned, a
> relation is a type, just as a bag is a type or a string, or name.
I don't think this is an implementation thing though - it's more fundamental than that. I think the system of predicates has to be isomorphic to the system of relations and unless you preserve things like atomicity this won't be the case.
>> Maybe there is some system of basic logic where lists are >> fundamental concepts but I'm not aware of it (and I'm not being >> facetious here).
>
> English? OK, I did take grad level logic courses once upon a time and
> I do recognize that a formal system of logic is important for
> querying the data, for example. But I use lists in English
> propositions often. Think of lists as connected by ANDs just as
> separate columns are except that they share the same type. What's so
> difficult about that? I guess the variable length of the list is
> one thing that could cause difficulty, but since it doesn't cause any
> difficulty in the environment in which I work, I suspect that any
> theorectical difficulty has work-arounds in the practical world.
Well if you google around you can find websites that approach logic from a more philosophical that mathematical angle, using sentences in a natural language. But they still basically parallel the mathematic definitions.
>> The second question is why not start with second order logic? Well, >> its theory is a lot more complicated and you get stuff like >> Godel's theorems biting you with things like unprovability and >> incompleteness.
>
> So what? Mathematicians have put up with Godel's theorem for quite
> some time and we haven't thrown out the Real numbers along with
> various operators because of it.
Good point. It is a bit unnerving to think that all you've got might be built on sand though. Interesting as well to see I think it was Dan's post about the practical difficulties he faced trying to build a system with nested relations.
>> Where I'm not totally clear is how much this has to do with >> infinities and whether the fact that databases are finite makes a >> difference, or whether their unboundedness is sufficient to cause >> problems.
>
> I don't know either. I would like to get my brain around this so I
> understand the arguements for eliminating lists in our data models.
Maybe there are two possible arguments:
1) simplicity, because we want to base it on standard first-order logic.
2) to avoid logical paradoxes or queries that return incorrect results
etc. I'd like to see some concrete examples of this though.
Argument 1 is the simple answer, argument 2 is a bit more esoteric.
Paul. Received on Sat Nov 06 2004 - 00:14:45 CET