W3C home > Mailing lists > Public > public-linked-json@w3.org > February 2013

Re: Problem with auto-generated fragment IDs for graph names

From: Ivan Herman <ivan@w3.org>
Date: Sat, 16 Feb 2013 08:40:46 -0500
Cc: Eric Prud'hommeaux <eric@w3.org>, Manu Sporny <msporny@digitalbazaar.com>, RDF WG <public-rdf-wg@w3.org>, Linked JSON <public-linked-json@w3.org>
Message-Id: <93B8ADE4-FFE9-4DC9-A3F5-66CE8903FF5B@w3.org>
To: Pat Hayes <phayes@ihmc.us>

On Feb 15, 2013, at 11:59 , Pat Hayes <phayes@ihmc.us> wrote:
> 
> OK, I am impressed. I wasnt aware that SPARQL allowed variables in graph name position. 
> 
> But let me ask you about this example. You are assuming here that the _:doc1 in the triple in the default graph, and the _:doc1 used as a graph label, refer to the same thing, which is the moon-green-cheese graph, right? What is interesting here is that this assumption seems inevitable when we have a bnode involved, as here, but (the WG has decided) it cannot be assumed when an IRI is used. So this data:
> 
> {ex:doc1 :author "Bob" }
> ex:doc1 {:TheMoon :madeOf :greenCheese }
> 
> does *not* entail that Bob is the author of the graph (since 'ex:doc1' might denote something else, which is what the default graph would be about, and not about the graph.) So this actually gives us a new, Manu-independent, reason to allow bnodes as graph labels in datasets: they provide exactly the missing expressivity that is needed to have the default graph act as genuine metadata.  
> 
> Hmm, I am now feeling like we should re-think our decision here. David, Guus, are you following this? Do I hear a groaning noise yet?
> 


First of all, I am not sure what 'our decision here' means in this case. I may infer that you want to re-think the 'can a bnode stand as a graph id' one, but I may also infer that you want to come back on 'graph label ... cannot be assumed when an IRI is used to refer to the graph'. I would be opposed to open the latter, that would mean another 1-2 years of discussion. 

As for the former: I must admit I do not really follow your reasoning. The way I see is that SPARQL does not define/say more about the referral in the case of blank nodes as for IRI-s, ie, there is no difference. The 

{IRI-OR-BNODE :author "Bob" }
IRI-OR-BNODE {:TheMoon :madeOf :greenCheese }

pattern meaning also referral seems to be more of a social convention to me rather than anything else; I do not believe SPARQL makes any statement whatsoever for this. What am I missing?

I must say that *if* there is a major semantic difference at this point between a bnode label and a IRI label, that may actually be an argument *not* to reopen this issue either; it would create an inconsistency that nobody would understand, let alone explain to third parties...

Ivan
 

----
Ivan Herman, W3C Semantic Web Activity Lead
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Received on Saturday, 16 February 2013 13:41:12 GMT

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