the goal of assembling an item in a certain quantity the propagation_subsearch can model a plan for a system to build that quantity of item and solve upstream problems that might occur based on that plan such as the need to assemble items that go into this particular assembly operation the evaluation_subsearch can evaluate the resultant plan after running the propagation_subsearch to ensure the resultant plan indeed builds the desired quantity if so the loop could be exited otherwise the cleanup_subsearch could reset the plan so that the next alternate can be explored for example if propagation_subsearch built items upstream but fell short of the desired quantity cleanup_subsearch can drive these quantity shortages downstream so that nothing is built downstream thus the u2018 problem u2019 can be restored to be solved by the next alternate plan by executing such scripts at various levels of the bill of materials a user can achieve sophisticated search through combinations of alternate plans another embodiment of the present invention can provide a general method of finding the best plan among various alternate plans such an embodiment can comprise a similar subsearch process as the previously discussed embodiment however rather than finding the first acceptable plan the script can direct the.