It is accepted that ontologies are vitally important for interoperability and information integration. The major part of every
ontology is its taxonomy, a hierarchy of the kind-of relation. Aconceptual relation seldom omitted from ontological considerations of a domain is the part-of relation. Guarino and Welty provide an ontology of properties which facilitates dealing with kind-of—we summarise their proposal from an order-theoretic perspective, and employ it to address part-of. We propose criteria and analyse the resulting classifications of the partof relation. The result is a step towards an ontology of part-of.