Re: One Ring to Bind Them
Date: Mon, 21 Jun 2004 20:23:04 +0300
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"Anthony W. Youngman" <wol_at_thewolery.demon.co.uk> wrote in message news:j$hPkhMcm30AFwso_at_thewolery.demon.co.uk...
> >Huh? I think you've missed Eric's point. As he said, the relational model
> >is based on predicates: sentences which make a single, descriptive
> >assertion. I confess that I don't fully understand the correspondence
> >between Pick internals and parts of speech, but the point is clear
> >nonetheless: our task in compiling databases, as I see it, is to be able
> >to accurately describe relevant parts ofthe world and draw inferences
> >those descriptions. It is from this premise that Eric's conclusion
> >follows: the best model for making descriptions of things is that whose
> >basic unit is description.
How could one infer in first order logic the number of employees for example ? :-)
> And I think that you've missed Bill's point. Predicates describe
> relational data. So Eric's point holds. But relational ASSUMES that
> relational data can be used to describe the real world - it's an axiom.
> Bill doesn't think that that holds in the real world, and I don't either
> which is why I asked the original question that started all this. Logic
> (ie predicates) is great for showing that a position is self-consistent.
> It is useless for showing that that position is relevant or useful.
How could you ensure that you get accurate (in concordance with the real world) answers from a database (managed with any kind of DBMS) if you want to count entities ? :-)
> But are you storing your constraints as a trigger? (Which I would
> sort-of consider an application in itself.)
> As I understand "the database", in order to store constraints in the
> database, you must store the constraints as *meta*data. Which means your
> end-user developers (programmer, dba, whatever) MUST be able to program
> *inside* the db engine so it can recognise metadata. At which point we
> get user-defined data types and your relational database has started
> down the road of mutating into an object database :-)
Well, user defined types does not necessarily mean dba defined types :-)
> Actually, I've just reread what you wrote. Do you mean "constraint" as
> in a relational constraint - foreign-key type stuff; or as a general
> term for enforcing integrity. I was thinking the latter, hence my
> reference to triggers, but I suspect you might be meaning the former. If
> you did mean the former, Pick doesn't have them because it achieves the
> same effect as a side-effect of its implementation. So the fact that
> relational needs them is de-facto a hindrance relative to Pick.
First order logic is so weak that it is almost guaranteed you'll need triggers for enforcing integrity. :-)
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