A rather long write-up but gives some context about why it's hard to build a graph data model as a layer on top of commodity non-graph databases: https://blog.d

A rather long write-up but gives some context about why it's hard to build a graph data model as a layer on top of commodity non-graph databases: https://blog.dgraph.io/post/why-google-needed-graph-serving-system/ https://blog.dgraph.io/post/why-google-needed-graph-serving-... (Obviously, the underlying storage layer of a graph db will use some sort of simpler storage layer, usually some kind of key value store)