Just in case if you are not aware check RDF/RDFS/OWL. Use cases are quite different but model wise there are similarities (no immutability / hash based tough).

Just in case if you are not aware check RDF/RDFS/OWL. Use cases are quite different but model wise there are similarities (no immutability / hash based tough). For example case how do you manage details of relationships of tags? Like how do you handle situation where you are accidentally created duplicate tag? Spoiler: There is not-so-small complexity creep there. I hope sane conscious trade-offs can be done.