Hmm... without serialization, and without an ORM solution, I would fall back to some sort of XML based implementation? You'd still have to design it carefully if you want to pull out only some of the objects from the object graph - perhaps a different file for each object, where object relationships are referenced by a URI to another file?
I would have said that wasn't "easy" because I've always found designing the mapping of XML to objects to be somewhat time consuming, but I was really inspired by a conversation on Apache Betwixt that has me feeling hopeful that I'm just out of date, and easier solutions are now available.
