I'm wondering if there are existing frameworks or libraries to create unstructured data objects or DTO using unstructured models. Instead of using structured classes as a mechanism for transferring data, I'd like to use an unstructured one with similar functionality to document-based models (hierarchical structure or arrays of arrays of fields with and fields referenced by a field identifier). It would be similar to (or might even be) XML but is geared towards being the mode if transporting data within an application (as opposed to between systems).

That way I'd have something like:

String lastName = "foo";
Model model = new Model();
model.add(FieldLastName.instance(), lastName);

Ideally it would have a toString() method that would dump the content to a String and maybe even create a model from a String, etc.

My apologies if I'm not phrasing this more solidly. I just don't know how else to phrase it.