Set the property identifier
        @type pid: string
        @param pid: property identifier

def set_id(self,pid):
        """
        Set the property identifier
        @type pid: string
        @param pid: property identifier 
        """
        if self.type == 'KAF':
            return self.node.set('pid',pid)
        elif self.type == 'NAF':
            return self.node.set('id',pid)