Abstract: A failure analysis system manages pieces of status information estimated by a diagnostic system together with indexes given to the pieces of status information, and builds up a tree-like index structure, wherein a logical relation analyzer and a failure path analyzer are incorporated in the failure analysis system so as to determine candidates of a failure propagation path in the tree-like index structure.

Abstract: A fault analyzing system presumes fault propagation paths for specifying nodes related to fault terminals once on plural time planes, and merges pieces of related fault terminal information representative of the fault terminals related to the nodes on different time planes in different manners so that plural list of plural kinds of fault are drawn up without repeating the time-consuming presumption.

Abstract: To realize high-speed error propagation path extraction in a combinational circuit, a logical contradiction judgment section detects the logical state of each signal line under the implication by a first implication section and judges whether the logical state of every signal line is estimated as “0,” “1,” or “X” unless a contradiction is detected. When it is judged that logical state estimation is not completed, a U(Unknown)-state retrieval section retrieves an Unknown-state signal line whose logical state is incomplete and retrieves a signal line connected to an error propagation path through a gate. A detected signal line is decided as “0,” a decision level showing a decision frequency is increased by 1, and implication is restarted by a first implication section.

Abstract: In evaluating the location of a failure in a logic circuit including gates defined in a hierarchical manner, the present invention discloses a system capable of evaluating the location of a failure by referring to the circuitry of a gate described by a basic gate without creating any special databases that are dedicated to evaluating the location of a failure. In this system, expected value setting device obtains an expected value of a target gate inside the logic circuit by an IF-THEN operation in an output direction, logical state evaluating device obtains a logical state of the target gate inside the logic circuit by an IF-THEN operation in an input/output direction, and a failure propagation path inside the target gate is obtained by comparing the expected value with the logical state.