That was my motivation for writing Hode[1], the Higher-Order Data Editor. It lets you represent arbitrarily nested relationships, of any arity (number of members). It lets you cursor around data to view neighboring data, and it offers a query language that is, I believe, as close as possible to ordinary natural language.
(Hode has no inference engine, and I don't call it an AI project -- but it seems relevant enough to warrant a plug.)