Currently, there is a hard coded list in RdfBuilder that determines which data type is a reference types (as per Iaf79a0012e6, that list is in PropertyRdfBuilder). This makes it impossible for extensions to declare additional reference types. Instead, the list of reference types should come from the DatatypeDefinitions class, which encapsulates the information from WikibaseRepo.datatypes.php.
Customize query in gerrit
|mediawiki/extensions/Wikibase||master||+42 -21||Move decision about reference types to WikibaseRepo.datatypes.php|