I don't think it encodes a graph that you query (like, say, Neo4J or Postgres with an orm); it seems to give various replicated data structure primitives, like documents, basically a kv store? So for building something like google docs.
You can likely build something SQL-like to form complex queries coordinating related objects, but the efficiency of such queries is not a given. You can likely manually build something like an index to speed up lookups using e.g. the map primitive. With a plan for a complex query, you're on your own.
Another likely problematic part is PK generation. You can of course use a counter, but I'm not sure how efficient will it be with burst inserts. For that, you'd have to come up with client-generated PKs that are unlikely to clash, e.g. UUIDs.
There is a lot of research still going on in the back, including indexing, access control, verification tools for apps, and some other really cool stuff.
Efficient support for queries is non-trivial, indeed.
