A diagnostic expert system incorporating a cause-effect graph is disclosed in which "yes", "no" and "unknown" are valid possible responses to a query. Each node in the graph is assigned a local decision factor (LDF) based on a given node's desirability for selection during best-first search and a collapsed...http://www.google.com/patents/US5018075?utm_source=gb-gplus-sharePatent US5018075 - Unknown response processing in a diagnostic expert system
