ISSUE-26 (Named graphs and default graph): Producing triples in named graphs and the default graph [R2RML]

ISSUE-26 (Named graphs and default graph): Producing triples in named graphs and the default graph [R2RML]

http://www.w3.org/2001/sw/rdb2rdf/track/issues/26

Raised by: David McNeil
On product: R2RML

>From the editor's draft of the R2RML spec (http://www.w3.org/2001/sw/rdb2rdf/r2rml/):

Section 1.4

"By default, all RDF triples are in the unnamed default graph of the RDF dataset. A TriplesMap can contain optional rules that place some or all of the triples into named graphs instead."

Section 3.3.1

"This optional property [, rr:graph, ] specifies a graph IRI. All the RDF triples generated from a logical table row will be stored in the specified named graph. In the following example, all the RDF triples generated from a logical table row will be in the named graph exa:DeptGraph."

The rr:graph property has a cardinality of "min=0, max=unlimited"

This seems to allow triples to be produced either in the default graph or a set of named graphs, but not in the default graph _and_ a set of named graphs. I think we need to clarify the wording to indicate which of these is intended:

1) Allow a TriplesMap to produce the triple for a logical row in the default graph and a set of named graphs. One way to achieve this would be to define a value for the rr:graph property that means "default graph". Alternatively the user would need to define another TriplesMap to produce the same triples in the default graph and named graphs.

2) Require that all of the triples are always produced in the default graph.

3) Only allow triples to be produced in either the default graph or a set of named graphs. This strikes me as an odd restriction.

An underlying issue to come to terms with is how the R2RML spec relates to the freedom the SPARQL spec (http://www.w3.org/TR/2008/REC-rdf-sparql-query-20080115/#exampleDatasets) allows for defining the relationship between the default graph and named graphs. Specifically it seems that the R2RML mapping is trumping the SPARQL implementation's ability to define the relationship between the default graph and named graphs.

Received on Wednesday, 2 March 2011 18:26:56 UTC