3.1.2 Enumerating and testing objects

Enumerating objects by role

[nondet]rdf_subject(?S)

True when S is a currently known subject, i.e. it appears in the subject position of some visible triple. The predicate is semidet if S is ground.

[nondet]rdf_predicate(?P)

True when P is a currently known predicate, i.e. it appears in the predicate position of some visible triple. The predicate is semidet if P is ground.

[nondet]rdf_object(?O)

True when O is a currently known object, i.e. it appears in the object position of some visible triple. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.

[nondet]rdf_node(?T)

True when T appears in the subject or object position of a known triple, i.e., is a node in the RDF graph.

[nondet]rdf_graph(?Graph)

True when Graph is an existing graph.

Enumerating objects by type

[nondet]rdf_literal(?Term)

True if Term is a known literal. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.

[nondet]rdf_bnode(?BNode)

True if BNode is a currently known blank node. The predicate is semidet if BNode is ground.

[nondet]rdf_iri(?IRI)

True if IRI is a current IRI. The predicate is semidet if IRI is ground.

[nondet]rdf_name(?Name)

True if Name is a current IRI or literal. The predicate is semidet if Name is ground.

[nondet]rdf_term(?Term)

True if Term appears in the RDF database. Term is either an IRI, literal or blank node and may appear in any position of any triple. If Term is ground, it is pre-processed as the object argument of rdf_assert/3 and the predicate is semidet.

Testing objects types

[semidet]rdf_is_iri(@IRI)

True if IRI is an RDF IRI term.

For performance reasons, this does not check for compliance to the syntax defined in RFC 3987. This checks whether the term is (1) an atom and (2) not a blank node identifier.

Success of this goal does not imply that the IRI is present in the database (see rdf_iri/1 for that).

[semidet]rdf_is_bnode(@Term)

True if Term is an RDF blank node identifier.

A blank node is represented by an atom that starts with _:.

Success of this goal does not imply that the blank node is present in the database (see rdf_bnode/1 for that).

For backwards compatibility, atoms that are represented with an atom that starts with __ are also considered to be a blank node.

[semidet]rdf_is_literal(@Term)

True if Term is an RDF literal term.

An RDF literal term is of the form String@LanguageTag or Value^^Datatype.

Success of this goal does not imply that the literal is well-formed or that it is present in the database (see rdf_literal/1 for that).

[semidet]rdf_is_name(@Term)

True if Term is an RDF Name, i.e., an IRI or literal.

Success of this goal does not imply that the name is well-formed or that it is present in the database (see rdf_name/1 for that).

[semidet]rdf_is_object(@Term)

True if Term can appear in the object position of a triple.

Success of this goal does not imply that the object term in well-formed or that it is present in the database (see rdf_object/1 for that).

Since any RDF term can appear in the object position, this is equaivalent to rdf_is_term/1.

[semidet]rdf_is_predicate(@Term)

True if Term can appear in the predicate position of a triple.

Success of this goal does not imply that the predicate term is present in the database (see rdf_predicate/1 for that).

Since only IRIs can appear in the predicate position, this is equivalent to rdf_is_iri/1.

[semidet]rdf_is_subject(@Term)

True if Term can appear in the subject position of a triple.

Only blank nodes and IRIs can appear in the subject position.

Success of this goal does not imply that the subject term is present in the database (see rdf_subject/1 for that).

Since blank nodes are represented by atoms that start with‘_:` and an IRIs are atoms as well, this is equivalent to atom(Term).

[semidet]rdf_is_term(@Term)

True if Term can be used as an RDF term, i.e., if Term is either an IRI, a blank node or an RDF literal.

Success of this goal does not imply that the RDF term is present in the database (see rdf_term/1 for that).