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')
        ]).