At first I was confused by this comment because anything built with links is a graph. Now that I've caught your meaning, and seen the complicated "included" structure, I wonder if it wouldn't have been better to just add an "_id" property to HAL. HAL's designers, however, would probably just say that "author" should be its own resource, and be linked or embedded as required. That is, if it's too heavy to embed, then link it.