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Comment on Dataset-UNION

From: Andy Seaborne <andy.seaborne@epimorphics.com>
Date: Tue, 22 Feb 2011 17:27:30 +0000
Message-ID: <4D63F202.8000903@epimorphics.com>
To: SPARQL Working Group <public-rdf-dawg@w3.org>
Dataset-UNION is defined to do an RDF merge - it should be set-union.

Graph store:
   DG: { _:a :q :r }

INSERT { ?x :p 123 . } WHERE { ?x :q :r }

then we get:

_:a :q :r .
_:x :p 123 .

because bnodes are not equated in a merge, but are renamed apart:

[[ http://www.w3.org/TR/rdf-mt/
if they do share blank nodes, then it is the union of a set of graphs 
that is obtained by replacing the graphs in the set by equivalent graphs 
that share no blank nodes. This is often described by saying that the 
blank nodes have been 'standardized apart'.
]]

it needs to be a set union.  Constant bnodes are treated by naming 
apart, for and every query solution, but not for bnodes arriving by 
variable substitution.

Dataset(modify_template,P) can handle the renaming apart, the 
dataset-union can then be a union.

	Andy

PS The link

<http://www.w3.org/2009/sparql/docs/update-1.1/definition%20in%20rdf-mt>
does not work.
Received on Tuesday, 22 February 2011 17:28:09 GMT

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