or a resources received event if in decision step 32 the message is a clock tick event the process agent object 200 in step 46 can interrogate the output production schedule of its corresponding process object 100 to determine if any work in process is complete if in step 34 any output has been completed in step 40 all completed output can be placed in output stack subsequently in step 44 all output in output stack can be passed to an adjacent upstream process agent object 200 for placement in the input stack of an associated adjacent upstream process object 100 in contrast if in decision step 36 the process agent object 200 detects a receipt of resources produced by an adjacent downstream process object 100 in step 38 the process agent object 200 can initiate production of output using all received resources placed in the input stack significantly the process agent object 200 initiates production regardless of the requirements of the adjacent upstream process object 100 subsequently the process agent object 200 can return to an idle state in step 42 while waiting for a new event fig6 a 6e taken together is a flow chart illustrating the event driven response of a process agent object 200 during a simulation of a pull system manufacturing process as applied to a pull system the system 1 can simulate process behavior by messaging instances of process agents objects 200 each controlling a portion of the manufacturing process fig6 a shows a message loop 66 for a process agent object 200 in step 50 the process agent object 200 can receive a message either from another instance of a process agent object 200 or from a process center agent object 210 controlling all instances.