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

On 7/8/2020 2:30 PM, Nicolas Chauvat 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".  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.
> 
> 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 ?
> 
> 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 ?
> 
> I would think that the open world assumption applies to nodes, not to
> values/literals. Am I missing something ?

Not exactly, but I'm saying it's not usually of much importance to say 
that the two literals are "the same" or not.  They aren't identifying 
anything, and very few literals except for URIs used as unique 
identifiers can do so.  It's really in the same league as whether the 
integer "2" in a given programming language is implemented as a 
singleton object or not (I understand that it is in Python).  It's much 
like an implementation detail.

Where the question could have some interest is if a particular literal 
could have a canonical and a non-canonical form;  Now the question of 
whether they are "identical" might have some significance.  That might 
come up in encryption, for example.  But in these cases we're talking 
about two literal forms that are not, on their face, identical, but that 
might resolve to the same canonical value.

TomP

Received on Wednesday, 8 July 2020 21:15:25 UTC