Unknown response processing in a diagnostic expert system

Claim 1

In a diagnostic expert system for solving a problem incorporating a cause-effect graph having a plurality of nodes and in which "yes", "no" and "unknown" are valid possible responsive inputs to a query, the method for processing in a computer which includes the following steps: (A) assign to each node in the cause-effect graph a local decision factor based on a given node's desirability for selection during a best-first search of the cause-effect graph; (B) assign to each node in the cause-effect graph a collapsed decision factor based on the values of the local decision factors for all daughter nodes of a current node; and (C) for the current node under examination having daughter nodes: (1) obtain a first list of all of the current node's daughter nodes; (2) examine the first list of daughter nodes and remove from the first list all daughter nodes on a closed list, a list of daughter nodes that have been visited before in examining a parent node of the current node which did not provide a solution to the problem, or whose prerequisites were not met; (3) remove from the first list all daughter nodes which have prerequisites that are not met, and add them to the closed list; (4) from the daughter nodes remaining on the first list, choose the daughter node with the largest local decision factor; and (5) identify a test function to be executed for the chosen daughter node, and query the result of executing the identified test function; (a) if the responsive input to a query produced in executing step (5) is a "yes", make the chosen daughter node the current node and return to step (C); (b) if the responsive input to a query produced in executing step (5) is a "no", delete the chosen daughter node from the first list and add it to the closed list and return to step (C); and (c) if the responsive input to a query produced in executing step (5) is an "unknown", compare the chosen daughter node's collapsed decision factor with the local decision factors for the other daughter nodes of the first list for the current node of the first list and which have their prerequisites met; and (i) if the collapsed decision factor of the chosen daughter node is larger than the local decision factors of the other daughter nodes of the list, make the chosen daughter node the current node and return to step (C); and (ii) if the collapsed decision factor of the chosen daughter node is not larger than the local decision factor of all of the daughter nodes of the first list, then choose the daughter node with the largest local decision factor and return to step (5).