1. In a rule processing system, a computer-implemented method of providing selection advice to help guide a user in selecting desired specifications of a product or service characterized by a ZDD rule model having one or more Include or Exclude rules, said method comprising: displaying multiple attributes and multiple enumerations thereof that identify available specifications of said product or service, selecting via a user interface multiple alternative enumerations of said attributes according to possibly desired specifications among said available, determining a selection advice for the enumerations selected in said selecting step, combining the selection advice for the enumerations determined in said determining step to produce a combined result, communicating to a user the combined result generated in the combining step, and using the result to choose a desired product or service having a compliant specifications among said possibly desired specifications.