Convert from RDF "type qualified literal" to Prolog atom in SWI Prolog

Question

The "SWI-Prolog Semantic Web Library 3.0" allows you to easily assert and query an RDF triple like this:

- rdf_assert(number, is, 1).
true.

?- rdf(number, is, X).
X = 1^^'http://www.w3.org/2001/XMLSchema#integer'.

How can you convert X from the "type qualified literal" format (described here) to a standard Prolog atom: X = 1?

I found xsdp_convert/3 but it needs the type ('http://www.w3.org/2001/XMLSchema#integer') and the value (1) passed in as separate arguments. How do I break apart the "type qualified literal" (1^^'http://www.w3.org/2001/XMLSchema#integer') to do this?

Or better yet: does that value^^type format actually mean something in Prolog and allow for a more elegant way to do it?

Answer 1

You can use unification, decompose the compound term that you get, or access its arguments:

?- use_module(library(semweb/rdf11)).
true.

?- rdf_assert(number, is, 1).
true.

?- rdf(number, is, N^^URI).
N = 1,
URI = 'http://www.w3.org/2001/XMLSchema#integer'.

?- rdf(number, is, X), X =.. List.
X = 1^^'http://www.w3.org/2001/XMLSchema#integer',
List = [^^, 1, 'http://www.w3.org/2001/XMLSchema#integer'].

?- rdf(number, is, X), arg(1, X, N).
X = 1^^'http://www.w3.org/2001/XMLSchema#integer',
N = 1.