<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def set_identifier(self, uid):
 """ Sets unique id for this epub :Args: - uid: Value of unique identifier for this book """


        self.uid = uid

        self.set_unique_metadata('DC', 'identifier', self.uid, {'id': self.IDENTIFIER_ID})