Concerning what kinds of things exist and how they relate. Where taxonomy ranks, ontology connects.
Greek ὄντος (ontos, of being), genitive of ὤν (ōn, being), from εἶναι (einai, to be); the adjective built from ontology, the study of what exists.
Concerning what exists and how it relates, as against taxonomy's concern with rank. The house's ontology connects; this word marks that it is connection, not order, under discussion.