If a CSP instance has no solution, it contains a smaller unsolvable subproblem that makes unsolvable the whole problem. When solving such instance, instead of just returning the “no solution” message, it is of interest to return an unsolvable subproblem. The detection of such unsolvable subproblems has many applications: failure explanation, error diagnosis, planning, intelligent backtracking, ...

The efficiency of Prolog compilers is increasing rapidly but the Prolog programs still cannot compete with traditional languages when executing simple conditionals. In this paper we present a possibility to increase Prolog performance by exploiting the shallow backtracking. Shallow backtracking is initiated when a call fails to unify with the head of a clause and it backtracks to another clause...

Abs t r ac t . We present a parallel graph narrowing machine, which is used to implement a functional logic language on a shared memory multiprocessor. It is an extensión of an abstract machine for a purely functional language. The result is a programmed graph reduction machine which integrates the mechanisms of unification, backtracking, and independent and-parallelism. In the machine, the sub...

We present here a discipline for job shop rescheduling based on partial order backtracking. We show that partial order backtracking ooers the rescheduler a framework for schedule repair, based upon a set of nogoods, which impose a systematic partial order on the set of activities to be repaired but allows non systematic techniques to be used within that framework. We present rescheduling as par...

Simulation modelling of the initial assignments of exams to time-slots provides an alternative approach to the establishment of a set of feasible solutions that are subsequently optimized. In this research, we analyze two backtracking strategies for reassigning exams after the initial allocation of exams to time-slots. We propose two approaches for backtracking, BT1 and BT2. The study indicates...

Teaching programming techniques has always been a challenge. We exhibit an innovative way of teaching the backtracking programming strategy using educational games, in particular Sudoku. Compared to traditional ways of teaching backtracking, we used a new pseudocode that corresponds to the solution tree of the educational game. Most of the current textbooks present the traditional way to teach ...

Goal-level Independent and-parallelism (IAP) is exploited by scheduling for simultaneous execution two or more goals which will not interfere with each other at run time. This can be done safely even if such goals can produce multiple answers. The most successful IAP implementations to date have used recomputation of answers and sequentially ordered backtracking. While in principle simplifying ...

We study of the operational behaviour of the speciication language Protocold. We examine whether BPA(+) (Basic Process Algebra with backtracking) forms a useful basis for a clear representation of the execution of certain language constructs from Protocold. Our primary focus is on those constructs that contain some form of backtracking. Backtracking in Protocold contains the undoing of bindings...

In this dissertation we investigate theoretical aspects of some practical approaches used in solving and understanding search problems. We concentrate on the Satisfiability problem, which is a strong representative from search problem domains. The work develops general theoretical foundations to investigate some practical aspects of satisfiability search. This results in a better understanding ...

The most advanced implementation of adaptive constraint processing with Constraint Handling Rules (CHR) allows the application of intelligent search strategies to solve Constraint Satisfaction Problems (CSP). This presentation compares an improved version of conflict-directed backjumping and two variants of dynamic backtracking with respect to chronological backtracking on some of the AIM insta...