Basic API

1 API for enumerating existing terms

Observations:

• rdf_resource/1 does not enumerate all resource-denoting terms. It enumerates the terms that are blank nodes or IRIs and that appear in the subject or object position of some triple.
• Enumeration based on positional occurrence (rdf_subject/1 and rdf_current_predicate/1) is missing object and node support.
• Enumeration based on kind (rdf_current_literal/1) is missing support for blank nodes, IRIs and names.

Proposal:

• Remove rdf_resource/1.
• Enumerate terms:
  • Add rdf_term/1, uniquely enumerating the current RDF terms.
• Enumerate terms based on their positional occurrence:
  • Keep rdf_subject/1 as-is.
  • Rename rdf_current_predicate/1 → rdf_predicate/1.
  • Add rdf_object/1 to complement rdf_subject/1 and rdf_predicate/1.
  • Add rdf_node/1, uniquely enumerating terms that occur in either the subject or object position.
• Enumerate terms based on their kind:
  • Rename rdf_current_literal/1 → rdf_literal/1.
  • Add rdf_bnode/1, uniquely enumerating terms that are blank nodes.
  • Add rdf_iri/1, uniquely enumerating terms that are neither blank node nor literal.
  • Add rdf_name/1, uniquely enumerating terms that are either IRI or literal.

2 API for creating new terms

Observations:

• Blank nodes and nodes are different concepts in RDF 1.1.

Proposal:

• Rename rdf_bnode/1 → rdf_create_bnode/1.
• Replace rdf_node/1 by the predicate described in section 2.1.

3 API for checking a term's kind

Observations:

• Kind checking (rdf_is_bnode/1 and rdf_is_literal/1) is missing support for IRIs.
• rdf_is_resource/1 does not succeed for all resource-denoting terms.

Proposal:

• Keep rdf_is_bnode/1 as-is.
• Keep rdf_is_literal/1 as-is.
• Rename rdf_is_resource/1 → rdf_is_iri/1.
• Change rdf_is_resource/1/rdf_is_iri/1 to not succeed for non-IRIs.

4 Relocate non-RDF predicates

Proposal:

• Rename and relocate rdf_md5/2. Mention in the documentation that this should not be used for security purposes (but there are many other applications where is can be useful).