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rdf_prefixes.pl -- RDF prefixes management
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This module defines the expansion of Prefix:Local terms to full IRIs. This library is typically not intended for the end-user. It may be included into other RDF and XML libraries and relevant parts may be re-exported.

Source rdf_empty_prefix_cache(+Alias, +URI)[multifile]
Multifile hook called if the binding Alias -> URI is modified. May be used to update derived caches.
Source rdf_current_prefix(:Alias, ?URI) is nondet
Query predefined prefixes and prefixes defined with rdf_register_prefix/2 and local prefixes defined with rdf_prefix/2. If Alias is unbound and one URI is the prefix of another, the longest is returned first. This allows turning a resource into a prefix/local couple using the simple enumeration below. See rdf_global_id/2.
rdf_current_prefix(Prefix, Expansion),
atom_concat(Expansion, Local, URI),
Source rdf_prefix(:Alias, +URI) is det
Register a local prefix. This declaration takes precedence over globally defined prefixes using rdf_register_prefix/2,3. Module local prefixes are notably required to deal with SWISH, where users need to be able to have independent namespace declarations.
Source rdf_db:ns(?Alias, ?URI) is nondet[multifile]
Dynamic and multifile predicate that maintains the registered namespace aliases.
- New code must modify the namespace table using rdf_register_ns/3 and query using rdf_current_ns/2.
Source rdf_register_prefix(+Prefix, +URI) is det
Source rdf_register_prefix(+Prefix, +URI, +Options) is det
Register Prefix as an abbreviation for URI. Options:
If true, replace existing namespace alias. Please note that replacing a namespace is dangerous as namespaces affect preprocessing. Make sure all code that depends on a namespace is compiled after changing the registration.
If true and Alias is already defined, keep the original binding for Prefix and succeed silently.

Without options, an attempt to redefine an alias raises a permission error.

Predefined prefixes are:

AliasIRI prefix
Source rdf_unregister_prefix(+Alias) is det
Delete a prefix global registration.
Source rdf_current_ns(:Prefix, ?URI) is nondet
- Use rdf_current_prefix/2.
Source rdf_register_ns(:Prefix, ?URI) is det
Source rdf_register_ns(:Prefix, ?URI, +Options) is det
Register an RDF prefix.
- Use rdf_register_prefix/2 or rdf_register_prefix/3.
Source register_file_prefixes(+Map:list(pair)) is det
Register a namespace as encounted in the namespace list of an RDF document. We only register if both the abbreviation and URL are not already known. Is there a better way? This code could also do checks on the consistency of RDF and other well-known namespaces.
To be done
- Better error handling
Source rdf_global_id(?IRISpec, :IRI) is semidet
Convert between Prefix:Local and full IRI (an atom). If IRISpec is an atom, it is simply unified with IRI. This predicate fails silently if IRI is an RDF literal.

Note that this predicate is a meta-predicate on its output argument. This is necessary to get the module context while the first argument may be of the form (:)/2. The above mode description is correct, but should be interpreted as (?,?).

- existence_error(rdf_prefix, Prefix)
See also
- rdf_equal/2 provides a compile time alternative
- The rdf_meta/1 directive asks for compile time expansion of arguments.
- Error handling is incomplete. In its current implementation the same code is used for compile-time expansion and to facilitate runtime conversion and checking. These use cases have different requirements.
Source rdf_global_object(+Object, :GlobalObject) is semidet
rdf_global_object(-Object, :GlobalObject) is semidet
Same as rdf_global_id/2, but intended for dealing with the object part of a triple, in particular the type for typed literals. Note that the predicate is a meta-predicate on the output argument. This is necessary to get the module context while the first argument may be of the form (:)/2.
- existence_error(rdf_prefix, Prefix)
Source rdf_global_term(+TermIn, :GlobalTerm) is det
Performs rdf_global_id/2 on predixed IRIs and rdf_global_object/2 on RDF literals, by recursively analysing the term. Note that the predicate is a meta-predicate on the output argument. This is necessary to get the module context while the first argument may be of the form (:)/2.

Terms of the form Prefix:Local that appear in TermIn for which Prefix is not defined are not replaced. Unlike rdf_global_id/2 and rdf_global_object/2, no error is raised.

Source rdf_meta(+Heads)
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.
The argument must be a resource. If it is a term prefix:local it is translated.
The argument is an object or resource. See rdf_global_object/2.
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.

Undocumented predicates

The following predicates are exported, but not or incorrectly documented.

Source rdf_register_ns(Arg1, Arg2, Arg3)
Source rdf_register_prefix(Arg1, Arg2, Arg3)