Returns <count> occupation updates from <offset>.
        
            An occupation update is a quadrupel

                (pc, source, timestamp, occupation)

def get_occupation_updates(self, offset=0, count=1000):
        """ Returns <count> occupation updates from <offset>.
        
            An occupation update is a quadrupel

                (pc, source, timestamp, occupation) """
        ret = []
        c = self.conn.cursor()
        for pc_id, source_id, datetime, occupation in c.execute(
                    """ SELECT pc, source, datetime, occupation
                            FROM occupationUpdates LIMIT ?, ? """,
                            (offset, count)):
            ret.append((self.id2pc_lut[pc_id],
                        self.id2source_lut[source_id],
                        datetime,
                        occupation))
        return ret