All in all this seems to be "graph databases, only the simplest parts", and yeah sure SQL can be coerced to traverse an acyclic directed graph, doesn't make for

All in all this seems to be "graph databases, only the simplest parts", and yeah sure SQL can be coerced to traverse an acyclic directed graph, doesn't make for a very efficient not interesting solution for the general case. Also calling a graph database a serialized tree structure seems quite a stretch.