W3C home > Mailing lists > Public > public-rdf-wg@w3.org > August 2013

Re: RDF-ISSUE-140 (dataset-comparison): RDF Dataset Comparison (Ivan Herman) [RDF Concepts]

From: Pat Hayes <phayes@ihmc.us>
Date: Sat, 10 Aug 2013 08:00:33 -0700
Cc: "'RDF Working Group'" <public-rdf-wg@w3.org>
Message-Id: <BBB51DE2-0234-47F7-AE98-3864B7278931@ihmc.us>
To: Markus Lanthaler <markus.lanthaler@gmx.net>

On Aug 9, 2013, at 7:53 AM, Markus Lanthaler wrote:

> On Friday, August 09, 2013 4:17 PM, Ivan Herman wrote:
>> On Aug 9, 2013, at 11:43 , Markus Lanthaler <markus.lanthaler@gmx.net>
> wrote:
>>> On Friday, August 09, 2013 11:24 AM, Ivan Herman wrote:
>>>> We had a long discussion some times ago and we concluded that graphs in
>>>> a dataset share bnodes. As a consequence, I believe Gavin's statement
>>>> seems to be the proper conclusion...
>>> 
>>> Yes, the graphs share bnodes but I'm not sure how that relates to the
> graph
>>> names. So you could as well argue that there are two sets of blank node
>>> identifiers and that in the examples below the mappings are
>>> 
>>> Example 1: _:y -> _:x (nodes) | _:y -> _:x (graphs)
>>> Example 2: _:y -> _:y (nodes) | _:y -> _:x (graphs)
>>> 
>>> Or do I miss something? As far as I understand it, there's no
> relationship
>>> between a blank node identifier used as graph name and a blank node
>>> identifier used as node (you could say they are in different scopes) from
>>> which I conclude that the same bnode id mappings can be mapped
> differently.
>>> 
>> 
>> Yes, we could do that. But that seems to be confusing, at least to me.

I agree. 
> 
> Yes, it's confusing. But I think it is a consequence of the decision to not
> define any dataset semantics. Blank nodes used as graph names do not denote
> the graph.

It is not a consequence of that. There are two different issues here. 1. Is it the same bnode? (A syntactic issue.) 2. Does a graph label denote the graph it labels?  (A semantic issue.) We have, regrettably, allowed the answer to 2 to be no, but that does not affect 1. 

> 
> 
>> Is there a use case for the separation of the different scopes?
> 
> Well, ask the people who voted against letting bnodes denote the graph.
> 
> 
>> It
>> looks way more obvious to me to consider a bnode as a label and a bnode
>> in one of the graphs as being identical...
> 
> Fully agreed, but I think under the current semantics they are not.

No, they can be the same bnode, but we don't impose the (obvious) condition that the labelling B: {G} means that I(B)=G. BUt that does not mean it is not the same bnode. 

Pat

> Actually
> the same is true for IRIs but since their scope is global the difference
> doesn't matter.
> 
> 
> --
> Markus Lanthaler
> @markuslanthaler
> 
> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Saturday, 10 August 2013 15:01:08 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 17:04:31 UTC