Generating an ordering of workflow items given a partial ordering and extension data

A computer-implemented method of processing items associated with a workflow includes accessing information that specifies, for each item to be processed, each of one or more primary input items that may be required under normal conditions to produce the item to be processed. The method also includes accessing information that specifies, for at least one primary input item, an alternative input item that may replace the primary input item under alternative conditions in producing the item to be processed. The items to be processed are ordered such that: (a) each item to be processed that has one or more primary input items is placed ahead of its primary input items; and (b) each primary input item that has one or more alternative input items is placed ahead of its alternative input items provided doing so is not inconsistent with the ordering of items ordered according to condition (a) and is also not inconsistent with the ordering of items ordered according to condition (b). The ordered items are processed according to the ordering using a software component.