Re: more on delete from join

Tegiri Nenashi wrote:
> On Aug 26, 2:14 pm, paul c <toledobythe..._at_oohay.ac> wrote:

>> Tegiri Nenashi wrote:
>>> On Aug 26, 1:03 pm, paul c <toledobythe..._at_oohay.ac> wrote:
>>>> I meant "AND" as the logical connective, not shorthand for relational
>>>> "<AND>".  "R AND A" stands for a logical conjunction of propositions,
>>>> each proposition having been concluded to be true.  
>>> Stop right there. You were writing R UNION A, so R and A are relations
>>> (or predicates) and not propositions. ...
>> Okay, I'll stop right there and be even more precise, relations are not
>> predicates, they are representations of predicates.  

I don't see how, except very casually. A relation is a set of ruples which is not the same thing as an intension or an extension but a relation can represent those to some extent if certain devices like equality and conventions like the CWA are used and the practicalities of recording negations can be avoided. A relational algebra expression can also stand in for a set of tuples, so it too could represent an intension or extension, but representing something is not the same as being the something.

Maybe the apparent difficulty in seeing the conclusion would go away if the analogy of two different roads to the same destination is used. Not very complicated if you ask me, nothing to do with infinite predicates either. Received on Thu Aug 27 2009 - 01:03:06 CEST