1. A method of operating a volume positioning mechanism in an automated library, the library having a plurality of volumes, a plurality of racks for storing the plurality of volumes and at least a first drive unit for recording data to or reading data from a volume mounted thereon by the volume positioning mechanism, the method comprising the steps performed by a data processing system of: processing each exogenous request for data in a volume to generate at least a first command for execution by the volume positioning mechanism; providing a command queue having a queue input level, a queue output level for the next scheduled command for execution and allowing a plurality of intervening levels; adding the at least first command to a command queue at the command queue input level; responsive to addition of a command to the command queue, selecting a command for each level in the queue by, qualifying commands for execution at a particular level, responsive to qualification of at least a first command for execution at the particular level, scoring each qualified command for execution at the particular level, placing the qualified command with the highest score in the command queue at the particular level and disqualifying the qualified command for consideration at any remaining levels; projecting a system state for after execution of the qualified command placed at a level in the command queue; and storing the projected system state with the command in the command queue; scanning the command queue for preselected patterns among adjacent commands; and responsive to location of an example of a preselected pattern, substituting a complex command for the adjacent commands.