What do people think about this potential approach for supporting
followup queries and PATCH operations involving blank nodes?
David Booth
-------- Forwarded Message --------
Subject: Re: deterministic naming of blank nodes
Date: Wed, 20 May 2015 17:55:30 -0400
From: David Booth <da...@dbooth.org>
To: Gregg Kellogg <gr...@greggkellogg.net>, henry.st...@bblfish.net
<henry.st...@bblfish.net>
CC: aho...@dcc.uchile.cl, semantic-...@w3.org
Hi Gregg,
On 05/20/2015 05:07 PM, Gregg Kellogg wrote:
[ . . . ]
Using a PATCH, you can’t reference existing BNodes. You _might_ be
able to in an UPDATE, as I indicated. A PATCH is typically described
as a series of deletes and adds (depending on the particular format);
for most cases SPARQL Update probably covers the use cases better.
My interpretation is that the deletes of a PATCH can’t really
reference BNodes in any way, unless the entire graph is removed.
Updates can, but they’ll always create new BNodes and can’t match
against existing ones.
If both client and server are working from the same known base-point,
and the PATCH is viewed as operating on the canonical *serialization* of
an RDF graph, such as in N-Triple, then it should work fine, just as
with any other text file.
However, currently there would be a problem in applying that PATCH to
RDF that is stored in a SPARQL server, because currently there is no
standard way to directly refer to a bnode from a separate SPARQL
operation. This is a known problem already with SPARQL, which causes
grief when doing followup queries. But if SPARQL servers were enhanced
to (optionally) enable subsequent queries or update operations to refer
directly to blank nodes by their *original* labels, then both PATCH and
followup queries would work on SPARQL servers. (In the case of implicit
bnodes generated by Turtle/SPARQL [] or () notation the server would
assign an original label.) This seems like a good route to take, though
it means adding that feature to SPARQL. I'll send this to the SPARQL list
https://lists.w3.org/Archives/Public/public-sparql-dev/
to see what others there think.
David Booth
