A telephone directory assistance system has been developed that uses natural language processing and mapping to reduce the time an operator spends looking for requested information. Its address analysis function has an average response time of 0.15 s with 99% accuracy. Its map guidance function has a response time of about 3 s for 100 KB of map data. Its search expansion function decreases operator's keying. Using this system, operators spend an average of 20% less time searching for information.

This correspondence demonstrates a new kind of error-checking scheme for multioutput combinational circuits and its use for a built-in testing method. In the error-checking logic employed, the output from the circuits being checked is partitioned into several groups. The predicted group parity is compared to that produced from the output in each group. This checking circuit, called a group-parity prediction (GPP) checker, can be implemented systematically. To ensure that the GPP checker is self-testing, several conditions are required. The self-testing GPP checkers are implemented for some concrete examples of multioutput combinational circuits. With respect to these examples, the self-testing GPP checker shows 87-100 percent error detection ability, and 91-100 percent fault coverage for single stuck faults. Using this self-testing GPP checker, a self-verification testing method, which takes advantage of the automatic fault-detection capability of a checker, is shown to be applicable to testing combinational circuits.