TDB version 0.8.5 and later
This feature allows a query to be made on a subset of all the named
graphs in the TDB storage datasets. The SPARQL GRAPH
pattern
allows access to either a specific named graph or to all the named
graph in a dataset. This feature means that only specified named
graphs are visible to the query.
SPARQL has the concept of a dataset description. In a query string, the clauses for FROM and FROM NAMED specify the dataset. The FROM clauses define the graphs that are merged to form the default graph, and the FROM NAMED clauses identify the graphs to be included as named graphs.
Normally, ARQ interprets these as coming from the web, that is the graphs are read using HTTP GET. TDB modifies this behaviour; instead of the universe of graphs being the web, the universe of graph is the TDB data store. FROM and FROM NAMED describe a dataset with graphs drawn only from the TDB data store.
TDB.symUnionDefaultGraph
is also set, then the default graph is set union of all the named
graphs (FROM NAMED).Example
#Follow a foaf:knows path across both Alice and Bobs FOAF data #where the data is in the datastore as named graphs. BASE <http://example> SELECT ?zName FROM <alice-foaf> FROM <bob-foaf> { <http://example/Alice#me> foaf:knows ?y . ?y foaf:knows ?z . ?z foaf:name ?zName . }