Matching patterns of facts to rule conditions in expert systems

摘要

In an expert system the matching of combinations of facts to rule conditions is such that the system can respond quickly to an external change requiring new fact information to be added. Fact information entered into the system is time-stamped and the time-stamp values for facts are put into a last-in-first-out stack. The matching operation involves the repeated and sequential execution of two main steps. In the first step a combination of facts, starting with the latest fact identified from the top of the stack, S1, is compared, S3, with the rule conditions. In the second step, if an external change is detected at S4 (e.g. as a result of an interrupt, or by polling) then the current match processing state is pushed on to the stack, S15, new fact information is input, S16, the new fact time-stamp is pushed on to the stack, S18, and the new fact is used, S1, as a seed for continuing the matching operation.