Re: WWW/Internet 2009: 2nd CFP until 21 September
Date: Fri, 14 Aug 2009 19:41:48 GMT
Message-ID: <06jhm.41254$PH1.2906_at_edtnps82>
Mr. Scott wrote:
> "paul c" <toledobythesea_at_oohay.ac> wrote in message
...;
>> How can four values be substituted into a predicate with six >> place-holders?
>
> I think the process is called currying. A n-ary predicate is a function of
> n variables that maps into the domain of truth values. Each row in a table
> is a function application that under the closed world assumption maps to the
> positive truth value. An incomplete row (a row with nulls) is a partial
> application that due to entity integrity still maps to the positive truth
> value. What remains is not a predicate but a formula with free variables
> that is known to be true.
>
>
So instantiation requires currying and the result of instantiation includes free variables! Sounds like what Bob B might have been expecting.
First I've ever heard that SQL depends on currying, let alone FOL and RA, didn't know they needed such an operation. Definitely sounds like a new RT operator (eg., couldn't possibly be a form of projection since that eliminates variables) for null fans..
Sarcasm aside, I'm pretty darn sure all logical formulae/wffs that are eligible RT propositions or constraints can be expressed in relational extensions, given enough storage. Maybe more to the point to say that If they can't, then they aren't eligible (eg., otherwise relations aren't closed under RT ops).. If the ones that aren't RT-eligible are somehow eligible to be expressed in SQL tables, then those tables can't be expressed by Codd's relations, which I guess is just another reason why SQL isn't relational and it is phony to say RT applies to SQL tables and phony to use RT arguments when talking about SQL. I'd like to know where is the SQL 'Theory'. Received on Fri Aug 14 2009 - 21:41:48 CEST