Abstract
This paper describes an explanation-based tools for constraint programming system. These tools provide to the user the conflicts when it raise during solving process. Our tools simulate constraint additions and/or constraint relaxations without any propagation; it also determine if a given constraint belongs to a conflict and it provide diagnosis tool ( e. g. why variable v cannot take value val?). With more user-friendly representation of conflicts and explanations, our proposed tools give better problem understanding to the user. We prooved that the proposed tools are efficient, and while there is no debugging system that allow the user to interact with the solver, our explanation-based tools could be used for many other applications. (C) 2007 Elsevier B.V. All rights reserved.