Connections Between the ATMS and AGM Belief Revision

The Assumption-based Truth Maintenance System (ATMS) [de Kleer, 1986] is the most wel l known implementation of any dynamic reasoning system. Some connections have been established between the A T M S and various nonmonotonic logics (e.g. autoepistemic logic [Reinfrank et al., 1989]). We describe the relationship between the A T M S and the A G M logic of belief [Gardenfors, 1988], and show that it is possible to simulate the behaviour of the A T M S using the A G M logic by encoding the justif icational information as an epistemic entrenchment ordering. The A T M S context switching is performed by A G M expansion and contraction operations. We present an algorithm for calculating this entrenchment ordering, and prove its correctness relative to a functional specification of the A T M S . This result demonstrates that the A G M logic, which is based on the coherence theory of just i f icat ion, is able to achieve both coherence and foundational style behaviour via the choice of epistemic entrenchments.