3.3.7 Graph manipulation

Many RDF stores turned triples into quadruples. This store is no exception, initially using the 4th argument to store the filename from which the triple was loaded. Currently, the 4th argument is the RDF named graph. A named graph maintains some properties, notably to track origin, changes and modified state.

[det]rdf_create_graph(+Graph)

Create an RDF graph without triples. Succeeds silently if the graph already exists.

[det]rdf_unload_graph(+Graph)

Remove Graph from the RDF store. Succeeds silently if the named graph does not exist.

[nondet]rdf_graph_property(?Graph, ?Property)

True when Property is a property of Graph. Defined properties are:

hash(Hash)

Hash is the (MD5-)hash for the content of Graph.

modified(Boolean)

True if the graph is modified since it was loaded or rdf_set_graph/2 was called with modified(false).

source(Source)

The graph is loaded from the Source (a URL)

source_last_modified(?Time)

Time is the last-modified timestamp of Source at the moment the graph was loaded from Source.

triples(Count)

True when Count is the number of triples in Graph.

Additional graph properties can be added by defining rules for the multifile predicate property_of_graph/2. Currently, the following extensions are defined:

• library(semweb/rdf_persistency)

  persistent(Boolean)

  Boolean is true if the graph is persistent.

[det]rdf_set_graph(+Graph, +Property)

Set properties of Graph. Defined properties are:

modified(false)

Set the modified state of Graph to false.