A method of using a plurality of subscriber types in managing a message queue of a database management system is described and provided. Each of the patterns further comprises a major symmetrical axis and a short axis, and each of the patterns is also composed of first units and second units, in which both the first unit and the second unit comprise respectively a plurality of light transmitting portions and light absorption portions. A second shuttle assembly is mounted in a wall of the bale case for reciprocation independently of the first shuttle assembly.