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

Re: New blank node scope proposal

From: Pat Hayes <phayes@ihmc.us>
Date: Tue, 22 Jan 2013 13:56:55 -0600
Cc: Antoine Zimmermann <antoine.zimmermann@emse.fr>, RDF WG <public-rdf-wg@w3.org>
Message-Id: <E1917AD2-FA95-49C1-9D54-B19BE92D4D22@ihmc.us>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>

On Jan 22, 2013, at 8:29 AM, Peter F. Patel-Schneider wrote:

> On 01/21/2013 09:47 PM, Pat Hayes wrote:
>> On Jan 21, 2013, at 8:10 AM, Antoine Zimmermann wrote:
>>> You can find my proposal at:
>>> http://www.w3.org/2011/rdf-wg/wiki/User:Azimmerm/Blank-node-scope
>> OK, let me pick up on this. Your second sentence is wrong, if it is supposed to be talking about current RDF as defined by the 2004 specs:
>> "The same blank node can appear in an infinity of RDF graphs and depending on which graph is considered, the blank node may indicate the existence of different things."
>> In current (2004) RDF, this is not correct. Each blank node is essentially an existential variable with a *global* scope. It is not limited to the particular graph in which it occurs. That is precisely the problem, in fact.
> This may be that is intended.   However, I don't see anything in the RDF Semantics that enforces it.

Not sure what would count as 'enforcement'. The semantics defines the meaning of a graph using the idea of a mapping from bnodes to denotations. It does not say, a mapping from a bnode in a context, or a bnode in a scope, just from a bnode. So, that mapping applies to that bnode wherever it - the bnode - occurs. Hence, if two graphs which just happen to contain the same bnode are united, its the same bnode in both of them. The intention was never to allow this curious circumstance (of the same bnode accidentally being used again in an unrelated graph) to arise, but we could not think of a sensible way to do it, so we were obliged to invent the merge/union distinction and reproduce the whole standardizing-apart machinery from machine theorem-proving (remember that stuff?). BUt now we can do it better, using scopes on bnodeIDs (not on bnodes!)


> [...]
> peter

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Received on Tuesday, 22 January 2013 19:57:25 UTC

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