1. A method for specifying a legality expression for use in a system for processing said legality expression, said method comprising: providing a legality expression language, including at least one of, a duty element specifying an obligation that a principal must perform an act, a ban element specifying a prohibition that a principal must not perform an act, an intent element specifying an intention that a principal wants to perform an act, and a claim element specifying an assertion that a principal does perform an act; and interpreting by said system a legality expression specified using said legality expression language.