Absolutely. But at that point we are quibbling over syntax instead of semantics, which is not that interesting. In practice you can do hierarchical models in SQ

Absolutely. But at that point we are quibbling over syntax instead of semantics, which is not that interesting. In practice you can do hierarchical models in SQL just fine (cf Oracle's ANCESTOR features, or AsterData's regexps), and bag-of-features stuff using JSON. Graph models are more awkward, but graph models are always awkward.