Yan Georget, Philippe Codognet, and Francesca Rossi. Constraint retraction in CLP(FD). Constraints, 4(1):5-42, February 1999. ISSN 1383-7133.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....to a CSP. Dynamic constraint solvers like DJCHR [21] or the system J.CP we are going to describe in this paper do not require state restoration techniques for search and are applicable to solve DynCSPs. These solvers provide a reverse operation to constraint posting, called constraint retraction [22, 10, 7]. With this operation arbitrary non deterministic search algorithms can be implemented that post and retract instantiation constraints [21, 17] The search algorithm posts instantiations to explore the search space and retracts them, if in inconsistency occurred due to their propagation. The ....

....used by constraints that were posted after the retracted constraint. The retraction is performed by rebuilding former variable domains from a history snapshot stored in the constraints that were a ected and by reposting all these constraints. Our algorithm is an adaption of retraction in CLP(FD) [10] where we abandon the use of a centralized history management by storing consequences of constraints locally (similar to [22] 2.2 Search in ACS In our prototypical ACS implementation J.CP we implemented two generic labeling constraints. The rst one uses Backtracking that allows complete ....

Yan Georget, Philippe Codognet, and Francesca Rossi. Constraint retraction in CLP(FD). Constraints, 4(1):5-42, February 1999. ISSN 1383-7133.

....these new techniques stick to the idea that former states are rebuilt and the action that was performed since then is re performed to remove erroneous input from the knowledge base. We provide an operation for incremental constraint retraction, like that available in DJCHR [18] or CLP(fd,S) [6], to reverse erroneous input. In di erence to the mentioned state restoring systems we do not compute (neither upward nor downward directed) former states, but states that would be the current state, if something were not done in the past . Unlike CLP(fd,S) or DJCHR we do not use a centralized ....

....of dom(v) constraint propagation) 3) The thus reduced variable domains may be used in later constraint executions. If c is retracted, these changes must be reversed in the system. Our constraint retraction algorithm, shown in Figure 4, is a mixture of the algorithms for retraction in clp(fd,S) [6] and deletion in DJCHR [18, 19] First we nd all constraints that may have been a ected by the retracted constraint from an internal storage of dependencies (like in [19] Second we enlarge the a ected variable domains to the maximum inferrable size (analogously to [6] And nally we repost all ....

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Yan Georget, Philippe Codognet, and Francesca Rossi. Constraint retraction in CLP(FD). Constraints, 4(1):5-42, February 1999. ISSN 1383-7133.

....or to nd all solutions to a CSP. Dynamic constraint solvers like our ACS implementation J.CP [14] or DJCHR [15] do not require state restoration techniques and are still applicable for dynamic problems. These solvers provide a reverse operation to constraint posting, called constraint retraction [16, 8, 7]. Thus arbitrary non deterministic search algorithms can be implemented that post instantiation constraints and reverse this operation, if an inconsistency has been detected [15] During search, dynamic solvers compute states, that would be the current state, if something would not have been done ....

....used by constraints that were posted after the retracted constraint. The retraction is performed by rebuilding former variable domains from a history snapshot stored in the constraints that were a ected and by reposting all these constraints. Our algorithm is an adaption of retraction in CLP(FD) [8] where we abandon the use of a centralized history management by storing consequences of constraints locally (similar to [16] 2.2 Search in ACS In our prototypical ACS implementation J.CP we implemented two generic labeling constraints. The rst one is Backtracking that allows complete ....

Yan Georget, Philippe Codognet, and Francesca Rossi. Constraint retraction in CLP(FD). Constraints, 4(1):5-42, February 1999. ISSN 1383-7133.

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