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Re: [Editorial] "blank nodes do not denote specific resources"

From: David Booth <david@dbooth.org>
Date: Thu, 19 Jul 2012 14:57:56 -0400
To: Pat Hayes <phayes@ihmc.us>
Cc: nathan@webr3.org, Eric Prud'hommeaux <eric@w3.org>, public-rdf-comments <public-rdf-comments@w3.org>
Message-ID: <1342724276.3486.15029.camel@dbooth-laptop>
On Thu, 2012-07-19 at 11:32 -0500, Pat Hayes wrote:
> On Jul 19, 2012, at 9:05 AM, David Booth wrote:
> 
> > On Thu, 2012-07-19 at 14:48 +0100, Nathan wrote:
[ . . . ]
> >>>>> "blank nodes indicate the existence of a thing, without providing a
> >>>>> name for that thing."
[ . . . 
> > So if we claim that it's not a name,
> > then we have to explain that we're using the word "name" in a special
> > way, and in general I think it's better to stick with plain English when
> > possible. 
> 
> [ . . . ] In RDF, a "name" is either a URI reference (soon to be an
> IRI) or a literal. 

But that definition of "name" does not appear in the current draft of
the Concepts document:
http://www.w3.org/TR/rdf11-concepts/
It appears only in the RDF Semantics document:
http://www.w3.org/TR/rdf-mt/#defname
And the reader of the Concepts document certainly should not be expected
to have read the Semantics document first.

> Blank nodes are not names and do not have any associated textual
> identifier.  This is all stated very clearly and simply in the RDF
> specs. Get used to it.

Certainly *I* am used to it, but this phrasing is in the introduction,
where the point is to help the new reader who is *not* yet used to it.  

Actually, stepping back a moment, a *very* common misunderstanding of
RDF is to confuse the RDF model with a particular RDF serialization.
There is some nice explanation in the RDF Semantics document of the fact
that a "node identifier" like _:xxx is not a "name" and does not exist
in the RDF graph:
http://www.w3.org/TR/rdf-mt/#graphsyntax
[[
[The N-Triples syntax] uses a node identifier (nodeID) convention to
indicate blank nodes in the triples of a graph.  While node identifiers
such as '_:xxx' serve to identify blank nodes in the surface syntax,
these expressions are not considered to be the label of the graph node
they identify; they are not names, and do not occur in the actual graph.
In particular, the RDF graphs described by two N-Triples documents which
differ only by re-naming their node identifiers will be understood to be
equivalent.
]]

Maybe a good way to help clarify this use of the word "name" and help
reduce that common misunderstanding of RDF is to pull some of that
explanatory material to the Introduction of the Concepts document,
perhaps rewording to refer to serialization in general, rather than just
N-Triples.


-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.
Received on Thursday, 19 July 2012 18:58:29 UTC

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