Re: Blank Nodes Re: Toward easier RDF: a proposal

On Thu, Nov 29, 2018 at 9:06 PM Pat Hayes <phayes@ihmc.us> wrote:

> On 11/28/18 9:41 AM, Henry Story wrote:
> >  I wonder if in that case 2. there is not a recipe for when one can
> merge such blank nodes. I don't think that semantically
> > the following two graphs G1 and G2 below are different:
>
> Correct. they are logically equivalent. In fact, G1 is non-lean
> and has G2 as an instance, so an efficient RDF engine could
> probably simplify G1 to G2.
>
> >
> > G1 =  {
> > :joe :address [ a "PostalAddress";
> >       :streetAddress "123 West Jefferson Street";
> >       :addressLocality "Phoenix";
> >       :addressRegion "AZ";
> >       :postalCode "85003";
> >       :addressCountry "US";
> >     ];
> >     :address [ a "PostalAddress";
> >       :streetAddress "123 West Jefferson Street";
> >       :addressLocality "Phoenix";
> >       :addressRegion "AZ";
> >       :postalCode "85003";
> >       :addressCountry "US";
> >     ].
> > }
> >
> >
> > G2 = {
> > :joe :address [ a "PostalAddress";
> >       :streetAddress "123 West Jefferson Street";
> >       :addressLocality "Phoenix";
> >       :addressRegion  "AZ";
> >       :postalCode "85003";
> >       :addressCountry "US";
> >     ].
> > }
> >
> > That would be satisfied in all the same models, it seems to me. No?
>
> Right, though you don't have to think about models if you prefer
> syntax. Just use the rule that A simply entails B exactly when B
> has an instance which is a subgraph of A (the 'interpolation
> lemma'). In this case, G2 is an instance of G1 and either half of
> G1 is an instance of G2.
>

for my own clarity:

and if we skolemize G1, then sk(G1) entails G1, and G2, but we can no
longer safely class one of the skolemized bnodes as redundant, since
they're no longer only existentially quantified - correct?

or more simply, as soon as we start skolemizing, throwing away redundant
nodes becomes a great deal more complex.

>
>