3.2.2 Enumerating objects

The predicates below enumerate the basic objects of the RDF store. Most of these predicates also enumerate objects that are not associated to any currently visible triple. Objects are retained as long as they are visible in active queries or snapshots. After that, some are reclaimed by the RDF garbage collector, while others are never reclaimed.

[nondet]rdf_subject(?Resource)

True if Resource appears as a subject. This query respects the visibility rules implied by the logical update view.

See also

rdf_resource/1.

[nondet]rdf_resource(?Resource)

True when Resource is a resource used as a subject or object in a triple.

This predicate is primarily intended as a way to process all resources without processing resources twice. The user must be aware that some of the returned resources may not appear in any visible triple.

[nondet]rdf_current_predicate(?Predicate)

True when Predicate is a currently known predicate. Predicates are created if a triples is created that uses this predicate or a property of the predicate is set using rdf_set_predicate/2. The predicate may (no longer) have triples associated with it.

Note that resources that have rdf:type rdf:Property are not automatically included in the result-set of this predicate, while all resources that appear as the second argument of a triple are included.

See also

rdf_predicate_property/2.

[nondet]rdf_current_literal(-Literal)

True when Literal is a currently known literal. Enumerates each unique literal exactly once. Note that it is possible that the literal only appears in already deleted triples. Deleted triples may be locked due to active queries, transactions or snapshots or may not yet be reclaimed by the garbage collector.

[nondet]rdf_graph(?Graph)

True when Graph is an existing graph.

[nondet]rdf_current_ns(:Prefix, ?URI)

deprecated

. Use rdf_current_prefix/2.