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Re: a blank node issue

From: William Waites <ww@styx.org>
Date: Wed, 2 Mar 2011 15:18:22 +0100
To: Pat Hayes <phayes@ihmc.us>
Cc: nathan@webr3.org, Ivan Shmakov <oneingray@gmail.com>, semantic-web@w3.org
Message-ID: <20110302141822.GC51897@styx.org>
* [2011-03-01 17:26:44 -0600] Pat Hayes <phayes@ihmc.us> écrit:

] No. Indeed, a blank node has no identifier, in the RDF abstract 
] graph syntax. However, this does not mean it has no semantic value

Fine as far as it goes. However if you descend into actual
real implementations this quickly becomes a problem. This
is why triplestores have some kind of skolemisation that
they do. 4store does bnode:abc123, Virtuoso does

Every time I have written a wrapper so that a library like
rdflib can talk to these stores, typically using SPARQL
over some sort of channel I have to write these special
cases in for the vendor extensions. Otherwise operations
like SELECT and DELETE cannot work predictably when
operating on a single statement containing a blank node.

So I know that several of us have seen this in practice
and had to deal with it one way or another, and obviously
the major triplestore authors have thought about it and
implemented vendor extensions, maybe some convention or
standard for skolemising blank nodes so they can be 
referred to might be a good thing?

William Waites                <mailto:ww@styx.org>
http://river.styx.org/ww/        <sip:ww@styx.org>
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Received on Wednesday, 2 March 2011 14:18:53 UTC

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