rdf_db:rdf_meta/1

This directive defines the argument types of the named predicates, which will force compile time namespace expansion for these predicates. Heads is a coma-separated list of callable terms. Defined argument properties are:

:: Argument is a goal. The goal is processed using expand_goal/2, recursively applying goal transformation on the argument.
+: The argument is instantiated at entry. Nothing is changed.
-: The argument is not instantiated at entry. Nothing is changed.
?: The argument is unbound or instantiated at entry. Nothing is changed.
@: The argument is not changed.
r: The argument must be a resource. If it is a term prefix:local it is translated.
o: The argument is an object or resource. See rdf_global_object/2.
t: The argument is a term that must be translated. Expansion will translate all occurences of prefix:local appearing anywhere in the term. See rdf_global_term/2.

As it is subject to term_expansion/2, the rdf_meta/1 declaration can only be used as a directive. The directive must be processed before the definition of the predicates as well as before compiling code that uses the rdf meta-predicates. The atom rdf_meta is declared as an operator exported from library(semweb/rdf_db). Files using rdf_meta/1 must explicitely load this library.

Beginning with SWI-Prolog 7.3.17, the low-level RDF interface (rdf/3, rdf_assert/3, etc.) perform runtime expansion of Prefix:Local terms. This eliminates the need for rdf_meta/1 for simple cases. However, runtime expansion comes at a significant overhead and having two representations for IRIs (a plain atom and a term Prefix:Local) implies that simple operations such as comparison of IRIs no longer map to native Prolog operations such as IRI1 == IRI2.