Back to Backtracking: Controlling the ATMS

The ATMS (A ssumption-Based Truth Maintenance Systern) provides a very general futility ior all types of default reasoning. One of the principal advantages of the ATMS is that cl11 of the possible (usually mutually inconsistent) solutions or partial solutions are directly available to the problem solver. By exploiting this capability of the ATMS, the problem solver can eficiently work on all solutions simultaneously and avoid the computational expense of backtracking. However, for some applications this ATMS capability is more of a hindrance than a help and some form of backtracking is necessary. This paper first outlines some of the reasons why backtracking is still necessary, and presents a powerful backtracking algorithm which we have implemented which backtracks more eficiently than other approaches. for problems where only one of a number of the possible solutions arc required. It achieves this efficiency by organixing the search to find a single specific solution first. By combining them we get the advantages of both.