Agile MDA is based on the notion that code and executable models are operationally the same. An executable model, because it is executable, can be constructed, run, tested, and modified in short incremental, iterative cycles. Hence, the principles of the Agile Alliance can be applied equally to models.
Many of the principles of XP and the Agile Alliance involve process and customer relationships and their management, not code. As such, the agile process principles for the construction of code apply just as well for the construction of executable models. For those principles that do specifically mention "code" or "software," an executable model, under this definition, is code.
To reach this happy state, models must be complete enough that they can be executed standing alone. Each model in a given set necessarily conforms to the same metamodel, because all models are equal there are no "analysis" or "design" models. Models are linked together, rather than transformed, and all of them are then mapped to a single combined model that's subsequently translated into code according to a single system architecture.