Hi, it is reasonably common in RDF vocabularies to see that a property is defined as an rdfs:subPropertyOf a blank node, such as in this example:
### vocabulary.ttl PREFIX : <http://example.com/> PREFIX owl: <http://www.w3.org/2002/07/owl#> PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> :p1 rdfs:subPropertyOf _:b1 . _:b1 owl:inverseOf :p2 . ### Example data using this vocabulary: ### data.ttl PREFIX : <http://example.com/> :e1 :p1 :e2 . ### When RDFS inference is applied to this data, using the vocabulary with Jena's command-line tool infer (the current 3.13.1 version, source code: https://github.com/apache/jena/blob/master/jena-cmds/src/main/java/riotcmd/infer.java), i.e. infer --rdfs vocabulary.ttl data.ttl, we get the following result (here prettified): ### PREFIX : <http://example.com/> :e1 :p1 :e2 ; _:b2 :e2 . ### As you can see, we infer that :e1 _:b2 :e2, which is invalid, because blank nodes (i.e. _:b2) are not permitted as predicates in RDF ( https://www.w3.org/TR/rdf11-concepts/#h3_section-triples). Now, it is clear how that follows from the rdfs:subPropertyOf inference rules (set aside that what we might actually want an RDFS/OWL reasoner that would give us :e2 :p2 :e1), but should such inference be made if it violates the RDF data model? I wonder if checking the produced inferences for validity is expensive, or if Jena's infer assumes a superset of RDF. Removing such inferences in post-processing is a bit tricky because RDF parsers recognize this as an error and fail. - Jindrich -- Jindrich Mynarz https://mynarz.net/#jindrich
