Execute a SPARQL query on an HTTP SPARQL endpoint. Query is an atom
that denotes the query. Result is unified to a term rdf(S,P,O) for
CONSTRUCT and DESCRIBE queries, row(...) for SELECT
queries and true or false for ASK queries. Options are
Variables that are unbound in SPARQL (e.g., due to SPARQL optional
clauses), are bound in Prolog to the atom '$null$'.
- endpoint(+URL)
- May be used as alternative to Scheme, Host, Port and Path
to specify the endpoint in a single option.
- host(+Host)
- port(+Port)
- path(+Path)
- scheme(+Scheme)
- The above four options set the location of the server.
- search(+ListOfParams)
- Provide additional query parameters, such as the graph.
- variable_names(-ListOfNames)
- Unifies ListOfNames with a list of atoms that describe the
names of the variables in a
SELECT query.
Remaining options are passed to http_open/3. The defaults for Host,
Port and Path can be set using sparql_set_server/1. The initial
default for port is 80 and path is `/sparql/`.
For example, the ClioPatria server understands the parameter
entailment. The code below queries for all triples using
_rdfs_entailment.
?- sparql_query('select * where { ?s ?p ?o }',
Row,
[ search([entailment=rdfs])
]).
Another useful option is the request_header which, for example,
may be used to trick force a server to reply using a particular
document format:
?- sparql_query(
'select * where { ?s ?p ?o }',
Row,
[ host('integbio.jp'),
path('/rdf/sparql'),
request_header('Accept' =
'application/sparql-results+xml')
]).
