According to https://query.wikidata.org/#%23List%20of%20property%20types%0ASELECT%20DISTINCT%20%3Fpropertytype%0AWHERE%0A{%0A%09%3Fproperty%20wikibase%3ApropertyType%20%3Fpropertytype%0A}%0ALIMIT%20100 we currently have 11 datatypes. The externalId datatype is missing at wikiba.se/ontology-1.0.owl and https://www.mediawiki.org/wiki/Wikibase/Indexing/RDF_Dump_Format. Might be missing in other places too.