Re: The MySQL/PHP pair

On Fri, 05 Nov 2004 23:14:45 +0000, Paul <paul_at_test.com> wrote:

>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.
>
>And I don't think relations are just another type - they are special
>because they represent your basic logical framework. All the other types
>are just tacked on afterwards to make life easier. Relations are the
>logic and the other types are the things that the logic talks about.
>
>>> 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.

3) It works. Don't fix it.

Seriously though, if you want to invent a new modelling paradigm, go right ahead, just don't call it Relational. Call it ... umm ... PICK.

Lemming

-- 
Curiosity *may* have killed Schrodinger's cat.