Re: Constraints and Functional Dependencies

From: paul c <toledobythesea_at_oohay.ac>
Date: Sun, 25 Feb 2007 00:12:48 GMT
Message-ID: <4w4Eh.1136338$R63.922574@pd7urf1no>

Marshall wrote:
> On Feb 24, 9:28 am, "Carl Federl" <cfed..._at_yahoo.com> wrote:
>

>><Anyone have any alternate formulas for functional dependencies or
>>candidate keys? >
>>
>>My primary objection to using FOL to define constraints is that it
>>would require our theory of data to have two different but similar
>>languages, one for defining constraints in the FOL language and then a
>>second language for manipulating relations.

>
>
> It is an interesting objection.
>
> For reasons I can't articulate, I find the RA easier for writing
> relational equations, and the RC easier for writing constraints.
> The difference is significant. (Anyone else care to weigh in on
> this?) If that holds at all widely, then it would be worth it to have
> both just for ease-of-use considerations.
>
>
> Marshall
>

Folklore has it that it's a big mistake to use RA, at least a stepwise version of it, for writing constraints because an engine will have little choice but to apply it verbatim. Whereas an engine will likely find it very convenient to convert whatever declarative constraint language to something resembling RA. However the same query might result in different generated RA on two different days.

p Received on Sat Feb 24 2007 - 18:12:48 CST