Pazzani and C. Brunk. Detecting and Correcting Errors in Rule-based Expert Systems: an Integration of Empirical and Explanation-based Learning. in Proceedings of the 5th Knowledge Acquisition for Knowledge-based Systems Workshop

program plan [ Johnson, 1986 ] , or existing correct program [ Murray, 1988 ] . By comparison, PDS6 and Forte are dynamic. They run a program on speci c examples, detect errors, and use them to revise the program. 2 Consequently, dynamic methods require only partial, extensional de nitions of programs. This is an important advantage since formal speci cations are frequently unavailable. Systems that require an existing correct program (e.g. Talus [ Murray, 1988 ] ) are primarily useful in tutoring environments, since a correct program is rarely available in other situations. Most other work in theory revision is propositional in nature, and therefore inapplicable to logic programming [ Ginsberg, 1990; Towell and Shavlik, 1991; Cain, 1991 ] . Focl [ Pazzani et al., 1991 ] uses an initial theory to guide a Foil-based system; however, it produces a at, operationalized de nition instead of a revised theory. A version of Focl that performs theory revision has been developed [ Pazzani and Brunk, 1990 ] ; however, it requires signi cant user interaction. Finally, Focl has not been tested on logic programming problems and it is unclear how its operationalization procedure would handle recursion.