<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _build_all_dependencies(self):
        '''
        Helper function to build a map of model to their list of model reference dependencies
        '''
        ret = {}
        for model, schema in six.iteritems(self._models()):
            dep_list = self._build_dependent_model_list(schema)
            ret[model] = dep_list
        return ret