Property P107 (http://www.wikidata.org/wiki/Property:P107) has emerged as Wikidata's de facto upper ontology. It currently consists of six main types: person, organization, event, creative work, term, and geographical feature. It's essentially a clean port of the high-level entities from the GND Ontology -- a controlled vocabulary developed by the German National Library and released last summer (http://d-nb.info/standards/elementset/gnd).

There's a fair amount of debate over that property. Are those current high level types (person, place, work, event, organization, term) a good fit for a knowledgebase that aims to structure all knowledge and not just library holdings? Does classifying subjects like inertia, DNA, Alzheimer's disease, dog, etc. as simply "terms" make sense?

More reading related to Wikidata, ontology and types: https://blog.wikimedia.de/2013/02/22/restricting-the-world/.