That's what I also don't quite get. I would build it as the parsing step mapped directly over the query. I suppose their approach lets them build a tree of operations but I'm skeptical it provides all that much benefit.
That would work if the API we were querying could return results of different types in response to a single query. But we might have a single operation that needs to know a couple of FooIds, a BarId, and a BazId, and they all need to be at least three requests against the remote system.
