Naming sparql service description's sd:NamedGraph
http://www.w3.org/TR/sparql11-service-description is a draft document describing how to describe what a SPARQL endpoint "is or can do". For example "do you accept SPARQL 1.1 queries?", and "what named graphs do you have?". This page is about the latter. In the examples that Greg and Ivan provide, blank nodes are used to (not) name the sd:NamedGraph instances that pair the named graphs in a SPARQL service with the SPARQL service itself (note that a named graph's name within two different endpoints ARE DISTINCT, and BOTH are distinct with the resource itself outside of the context of a SPARQL service).
However, I need to give the sd:NamedGraph a URI so that I can refer to it when describing the provenance of data loaded into the named graph. Is there a "good" URI we can use? YES! This page describes how to create a canonical URI for a sd:NamedGraph that conforms to Linked Data principles and nicely uses the SPARQL service itself to provide the functionality. The approach reuses the SPARQL endpoint's namespace to provide a nice canonical method to name any of its named graphs -- without inappropriately stomping on someone else's namespace.
TODO: discuss http://www.w3.org/TR/sparql11-http-rdf-update/#indirect-graph-identification
An illustration of the full vocabulary:
An illustration of the example provided at http://www.w3.org/TR/sparql11-service-description/#example-turtle:
sparql-service-descriptions.xsl queries a SPARQL endpoint for all named graphs and returns a SPARQL Service Description.
Loading the following RDF into http://logd.tw.rpi.edu:8890/sparql's named graph https://github.com/timrdf/csv2rdf4lod-automation/wiki/Naming-sparql-service-description%27s-sd%3ANamedGraph (Apologies for this endpoint not abstracting away from implementation details (i.e., its port)):
@prefix sd: <http://www.w3.org/ns/sparql-service-description#> .
[] a sd:Service;
sd:url <http://logd.tw.rpi.edu:8890/sparql>;
sd:defaultDatasetDescription [
a sd:Dataset;
sd:namedGraph [
a sd:NamedGraph;
sd:name
<https://github.com/timrdf/csv2rdf4lod-automation/wiki/Naming-sparql-service-description%27s-sd%3ANamedGraph>;
];
]
.
We can query it to get an RDF description of where it is (i.e, the named graph of a particular SPARQL endpoint) (results):
PREFIX sd: <http://www.w3.org/ns/sparql-service-description#>
CONSTRUCT { ?endpoints_named_graph ?p ?o }
WHERE {
GRAPH
<https://github.com/timrdf/csv2rdf4lod-automation/wiki/Naming-sparql-service-description%27s-sd%3ANamedGraph> {
[] sd:url <http://logd.tw.rpi.edu:8890/sparql>;
sd:defaultDatasetDescription [
sd:namedGraph ?endpoints_named_graph
]
.
?endpoints_named_graph
sd:name
<https://github.com/timrdf/csv2rdf4lod-automation/wiki/Naming-sparql-service-description%27s-sd%3ANamedGraph>;
?p ?o .
}
}
Cleaning out the junk variables bundled into the URL:
and normalizing its white space, we now have a generic way to create a URI for a named graph within a particular SPARQL endpoint:
Now, if the SPARQL service has the named graph, and a service description is within this named graph describing itself, then a snippet of RDF will be returned when requesting the named graph's URI. Note that the service description doesn't actually need to be in the named graph for the URI to be "valid" (since "valid" doesn't even make sense) -- it just means that IF it were there, THEN we'd get some "interesting" RDF back describing it. The perfect canonical URI, created by anyone and responsive without modification to the SPARQL service implementation.