Re: more closed-world chatter
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 06 May 2007 16:30:19 -0300
Message-ID: <463e2c9b$0$4044$9a566e8b_at_news.aliant.net>
>
> (I didn't think I was proposing second-order.)
>
> I was imagining a catalog table/relation such as
> TYPES{attributename,type} where attributename is key, which I think is
> what you mean too.
>
> It doesn't bother me (yet) that I might fail to create a relvar because
> an attribute was already defined with a different type because, once all
> relvars were defined, I would rather have an engine that would operate
> with as few exceptions as possible.
Date: Sun, 06 May 2007 16:30:19 -0300
Message-ID: <463e2c9b$0$4044$9a566e8b_at_news.aliant.net>
paul c wrote:
> Marshall wrote:
>
>> On May 6, 9:49 am, paul c <toledobythe..._at_oohay.ac> wrote: >> >>> Not to distract my betters on this topic, but I guess I should have >>> originally mentioned that I think the D&D stipulation "It is required >>> that if <A,T1> is in Hr1 and <A,T2> is in Hr2, then T1 = T2" could be >>> gotten around simply by ensuring that no two relvars have such an >>> attribute. This would be easy for a "catalog" to enforce. >> >> >> >> Sure, that works. But it doesn't thrill me; it means that now you >> might be trying to create a relvar and fail because of some >> other relvar that you're barely aware of. >> >> My latest thinking is just to take T1 and T2 out of the header >> and put them on the constraints. That means you don't need >> any second-order constraints like the one you propose, and >> it furthermore means you can join any two relations and be >> sure of getting a relation. (I.e. closure.)
>
> (I didn't think I was proposing second-order.)
>
> I was imagining a catalog table/relation such as
> TYPES{attributename,type} where attributename is key, which I think is
> what you mean too.
>
> It doesn't bother me (yet) that I might fail to create a relvar because
> an attribute was already defined with a different type because, once all
> relvars were defined, I would rather have an engine that would operate
> with as few exceptions as possible.
[snip]
The more you reduce exceptions the more you increase quiet tolerance for absolute gibberish. Received on Sun May 06 2007 - 21:30:19 CEST