I realized, I forgot to complete my sentence here: "...because of this every semi-structured graph model historically has been extended with a schema." Examples include, XML and RDF. More relevant to this discussion: there is an ongoing effort to define a graph schema in GQL, which is an industry-academia effort including I think all major players: Neo, Tiger, Oracle etc. (https://www.gqlstandards.org/home).

You can search for this on the link: "GQL will incorporate this prior work, as part of an expanded set of features including regular path queries, graph compositional queries (enabling views) and schema support."