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

> 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  
>

Received on Thursday, 9 July 2020 01:40:16 UTC