1. In a rule processing method utilizing a Zero-suppress Decision Diagram (ZDD) rule model to define compliant features characterized by attributes and enumerations of a product or service, a computer-implemented method of providing selection advice to choose among compliant features characterized by multiple rule components of the ZDD rule model, the method comprising: identifying a central one of the rule components having a pending value of an enumeration not yet selected; determining selection advice for at least one enumeration of at least one rule component directly related to the central one of the rule components based on possible selections of enumerations of other rule components directly related to the central one of the rule components but indirectly related to the at least one rule component responsive to the identifying; displaying results of the selection advice based on the possible selections of the enumerations; and using the results to choose among enumerations that render specifications of the product or service compliant; where each of the multiple rule components directly relates to the central one of the rule components; and where the at least one rule component does not directly relate to at least another of the multiple rule components.