is shown in dotted arrows 102 the mark facility controller 74 accepts mark job descriptions from a mark facility client such as a print service or copy service the main component of this job is the assembly tree which specifies the physical assembly of the document s to be produced the assembly tree definition is independent of the dot that will produce the job the assembly tree references images which are stored outside of the mark facility controller jobs are queued in the mark job queue 94 and then go to the scheduler 96 to begin execution the scheduler understands and models the machine modules in terms of capabilities and constraints which are uploaded into the mark facility controller at power up time and stored in the constraint store 110 the scheduler 96 coordinates the various machine modules 104 106 108 e g feeder modules image path modules marker modules finisher modules and output modules to produce the job the scheduler also coordinates the image loader 98 which is viewed by the scheduler as just another machine module one that happens to feed images rather than paper the image loader acts as a 34 flowcontrol 34 valve pulling the images out of the image store and transferring them to a marking module at the scheduled time note that there are two fairly independent paths the control path and the image path these two paths intersect at the image loader the mark facility controller accepts mark jobs and other communication from mark facility clients and controls the overall operation of the machine modules.