# Re: more on delete from join

From: paul c <toledobythesea_at_oohay.ac>
Date: Tue, 01 Sep 2009 17:03:12 GMT
Message-ID: <ktcnm.43362\$PH1.627_at_edtnps82>

Mr. Scott wrote:
...
> An appeal to logic. Affirming the disjunction of two ground atoms,
>
> Pabc OR Qabc
>
> implies that either Pabc is true or Qabc is true or both are true.
> Similarly, denying the conjunction of two ground atoms,
>
> NOT (Pabc AND Rabd),
>
> is equivalent to affirming the disjunction
>
> NOT Pabc OR NOT Rabd
>
> which implies that either Pabc is false or Qabd is false or both are false.
> Either case involves affirming a disjunction, not a conjunction.
> ...

> Now let's apply this logic to relational theory. Let there be tables with
> predicates P, Q and R, a view that is the union of the table with predicate
> P and the table with predicate Q, and a view that is the join of the table
> with predicate P and the table with predicate R. Inserting a row (a,b,c)
> into the union view affirms the disjunction Pabc OR Qabc; deleting a row
> (a,b,c,d) from the join view affirms the disjunction NOT Pabc OR NOT Rabd.
> Both inserts into the union view and deletes from the join view affirm
> disjunctions, and as a consequence, neither inserts into the union view nor
> deletes from the join view have unique results.
>
> I can see the benefit of recording disjunctive information. If it is known
> that A OR B is true, then it should be possible to assert A OR B, even if it
> is not known which is true. I just don't think that an insert into a union
> view is the correct way to do it. A better way would be to use three
> tables, one for facts like 'It is known that A.' one for facts like 'It is
> known that B.' and one for facts like 'It is known that A OR B, but not
> which.'
> ...

That's a clear, logical and very direct position. Mine is more complicated, maybe I should try to be more formal about it. Received on Tue Sep 01 2009 - 19:03:12 CEST

Original text of this message