Re: Blank nodes must DIE! [ was Re: Blank nodes semantics - existential variables?]

Hi Patrick

Thank you for the time granted in answering my questions. I'll try to keep
it focused and work on the fire management with you 😂

there is nothing corresponding to the ‘reference’ case
>

If I were to merge two graphs, both containing URLs and bnodes, I'd retain
the URLs, but I'd create new bnode IDs (to avoid potential problems if the
graphs happened to use some bnode IDs that were the same). So maybe it's
just my terminology, but the retaining of original identifiers, the URLs in
this case, is the reference case.

How do you ever know when you have all the necessary properties?
>

Yeah, that's the problem being discussed earlier in the thread about
type-dependent comparison operations for value types, and David's
discussion about keys.

you might want to assign a URI to a literal value ... it shouldn't be
> illegal
>

Agree, it shouldn't be illegal.

Blank nodes don't have types.
>

When I say blank nodes have a type I'm being sloppy, sorry. I mean the
things they refer to, of course.

If this were RDF, what would this distinction (between class and datatype)
> /mean/?
>

Something being an instance of a datatype would be an instruction to not
rely on the identifier to find equivalents, but to (somehow) look up
prescribed comparison operations for that type. It'd also be an instruction
that those instances are better off not being skolemized and should be
passed along to the next consumer as is. It'd basically be an instruction
to treat the individual like a literal when trying to reason about the
graph.

Regards
Anthony

On Wed, Jul 8, 2020 at 6:46 PM Patrick J Hayes <phayes@ihmc.us> wrote:

>
>
> > On Jul 8, 2020, at 1:30 PM, Nicolas Chauvat <nicolas.chauvat@logilab.fr>
> wrote:
> >
> > On Wed, Jul 08, 2020 at 11:54:16AM -0400, Thomas Passin wrote:
> >> Here's what I am thinking of, and I'll talk about points, since that
> was the
> >> ...
> >> Or put another way, just because the same literal value is assigned to
> two
> >> nodes does not make them the same.  Is that literal value itself the
> "same"
> >> for both?  In some software it might be - if it's been memoized, for
> example
> >> - but that's normally an implementation detail, not something
> fundamental.
> >
> > When I say that (1,2) is a true value, aka an immutable struct, your
> > answer is that two (1,2) values are not the same because, taking into
> > account the open world assumption, they could have a third dimension
> > (or some other attribute).
> >
> > You write "the same literal value is assigned to two nodes, does not
> > make them the same”.
>
> Um.. with one plausible interpretation, that is wrong. (RDF does not have
> the notions of ‘assignment’, and ’same’ is ambiguous, but ploughing ahead…)
> Lets use owl:sameAs to attach a literal value to a URI:
>
> ex:this owl:sameAs “17”^^xsd:integer .
> ex:that owl:sameAs “17”^^xsd:integer .
>
> and now ask, are this and that the same?:
>
> ex:this owl:sameAs ex:that . ??
>
> and the answer is always, Yes. This is entailed by the first two triples.
> Of course they are not the same URI, but they have the same denotation
> (value).
>
> >  Is it correct to rephrase that as follows ?
> >
> >  p1 has_coords (1,2)
> >  p2 has_coords (1,2)
> >
> > In that case I agree that nothing proves p1 and p2 are the same.
>
> True.
> >
> > But what I am pointing at when I talk about an immutable struct is not
> > the above.
> >
> > A better comparison would be "2002-05-30T09:00:00"^xsd:datetime, that
> > could be deserialized to (year: 2002, month: 5, day: 30, hour: 9,
> > minutes: 0, seconds: 0).
> >
> > Would you say that the two literals
> > "1;2"^<http://mydomain.com/mytypes/tuple-of-two-integers> and
> > "1;2"^<http://mydomain.com/mytypes/tuple-of-two-integers> are
> > different things ?
>
> Better not say that, as it would be flat wrong :-)
> >
> > Does it follow from the open world assumption that
> > "2002-05-30"^xsd:date and "2002-05-30"^xsd:date are different values
> > because one could append the time information and write
> > "2002-05-30T09:00:00"^xsd:datetime ?
>
> No. It has absolutely nothing to do with the OWA. Adding more information
> to an RDF graph cannot change the meaning of a literal, whether the world
> is open or closed. The meanings of literals are defined externally to the
> RDF spec, by the specs for the datatype of the literal. So whatever the RDF
> graph says about those literals, their value does not change.
>
> Pat
>
> >
> > I would think that the open world assumption applies to nodes, not to
> > values/literals. Am I missing something ?
> >
> > --
> > Nicolas Chauvat
> >
> > logilab.fr - services en informatique scientifique et gestion de
> connaissances
> >
>
>
>