## The 5th Workshop on Constraint Handling Rules (2008)

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@MISC{Schrijvers08the5th,

author = {Tom Schrijvers and Frank Raiser and Thom Frühwirth (editors and F. Lichtenberger and P. Paule and H. Rolletschek and J. Schicho and C. Schneider and W. Schreiner and Thom Frühwirth},

title = {The 5th Workshop on Constraint Handling Rules},

year = {2008}

}

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### Abstract

This book contains the proceedings of CHR 2008, the fifth workshop on Constraint

### Citations

1608 | A Note on two Problems in Connexion with Graphs
- Dijkstra
- 1959
(Show Context)
Citation Context ...have been considered which can be added to the query interpreters. For PrioALPs without integrity constraints, we can perform a pruning analogous to what happens in Dijkstra’s shortest path algorithm =-=[27]-=-. Whenever we have two or more processes with the same remaining subgoal (e.g., for finding a path from the same intermediate node to the terminal node in the shortest path example), we keep only the ... |

547 | The role of abduction in logic programming
- Kakas, Kowalski, et al.
- 1998
(Show Context)
Citation Context ...-based tabling. However, this approach requires excessive data structure implementation, does not enable further rule specialization, and does not easily compose with other indexes. The join-calculus =-=[19]-=- features multi-headed rules that are similar in nature to CHR’s rules. However, the expressivity of these rules is severly limited: arguments cannot be matched and rules cannot be otherwise guarded. ... |

423 | Theory and practice of constraint handling rules
- Frühwirth
(Show Context)
Citation Context ...ttening overhead. We compare our techniques with the current state of the art in CHR compilation, and measure their efficacy in K.U.Leuven CHR and CHRd. 1 Introduction Constraint Handling Rules (CHR) =-=[1]-=- is a high-level rule-based declarative programming language, usually embedded in a host language such as Prolog or Haskell. Typical applications of CHR include scheduling [2] and type checking [3]. C... |

157 | The Independent Choice Logic for modelling multiple agents under uncertainty
- Poole
- 1997
(Show Context)
Citation Context ...we obtain:sTransformation-based Indexing Techniques for Constraint Handling Rules 11 d’(A,B,N) <=> X = ψ(A,B), N>0 | (A1,B1) = φ(X), d’(A1,B1,N-1). We refer the reader to the work of Tacchella et al. =-=[13]-=- for the formal definition and correctness proof of unfolding of CHR rules. Step 2: Eliminate flattening after unflattening. Apply the following equation from left to right: ∀t : φ ◦ ψ(t) = t which is... |

121 |
Logic for improving integrity checking in relational data bases. Acta Inform
- Nicolas
- 1982
(Show Context)
Citation Context ...are deemed not to become best in the end. We mention also the possibility to apply simplified integrity constraints in specialized rules for each abducibles predicate. Simplification was suggested by =-=[28]-=- for database integrity checking; an unfolding of the theoretical foundations and a powerful method is given by [29]. We show here how this applies to the integrity checking shown in the code fragment... |

53 | ACLP: Abductive constraint logic programming
- Kakas, Michael, et al.
- 2000
(Show Context)
Citation Context ...th systems. In K.U.Leuven CHR only gamma prime and listdom suffer performance slow-downs, whereas other benchmarks show run-time improvement. This success is caused by the system’s guard optimization =-=[15]-=-, which detects dead code for the specialized constraint symbols. Post-processing considerably improves the performance of listdom and eliminates the overhead of gamma prime. It has no significant eff... |

50 | A Prolog-like inference system for computing minimum-cost abductive explanations in natural-language interpretation
- Stickel
- 1988
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Citation Context ... CHRat program, variables in ask ∗ (CCHR) and entailed ∗ (CCHR) are in x. Thus ⊢C • (ri) ‡ ↔ (�ri�) † . 5 Examples 5.1 Union-Find Constraint Component The union-find (or disjoint set union) algorithm =-=[14]-=- has been implemented in CHR with its best-known algorithmic complexity [15]. This positive result is remarkable because logic programming paradigm has been known to be ill-suited to such implementati... |

47 | A-system : Problem solving through abduction
- Kakas, Nuffelen, et al.
- 2001
(Show Context)
Citation Context ...asoning in CHR ∨ Both CHR ¬ and CHR ∨,naf share the same syntax, but differ substantially in their semantics. The semantics for CHR ¬ was based on the refined operational semantics for CHR defined in =-=[16]-=- and consisted of restricting the applicability of CHR rules to situations where no negated head were present and adding the notion of Triggering on removal, in which, a rule should also fire when a n... |

37 | An experimental CLP platform for integrity constraints and abduction
- Abdennadher, Christiansen
- 2000
(Show Context)
Citation Context ...antics. 1 Introduction Constraint Handling Rules (CHR) [1] is a concurrent committed-choice constraint logic programming language to describe rewritings among multi-sets of constraints. Join-Calculus =-=[2]-=- is a process calculus designed to provide expressive concurrency abstractions in the form of reaction rules, known as Join-Patterns. Rule triggering depends on the availability and simultaneous consu... |

37 | The CIFF proof procedure for abductive logic programming with constraints
- Endriss, Mancarella, et al.
- 2004
(Show Context)
Citation Context ... for symbol specialization arises naturally in the context of partial evaluation [16]. Similar, but less ambitious in scope, is the work on constructor specialization for the Glasgow Haskell Compiler =-=[17]-=-. These two approaches, for single-headed languages, aim in the first place at reducing intermediate data structures and matching costs, and specializing the body. In contrast, the foremost goal of ou... |

31 |
Cost-based abduction and map explanation
- Charniak, Shimony
- 1994
(Show Context)
Citation Context ...lvers are awoken with ask(·) tokens (Ask rule); then, when all ask solvers have answered positively to the guard with entailed(·) tokens, the body of the rule is fired (Fire rule). Unlike deep guards =-=[12]-=-, asks are thus checked in CHRat in the same constraint store as tells.sModular CHR with ask and tell 101 Definition 8. A computation of a goal G is a sequence S0, S1, . . . of configurations with Si ... |

24 | HYPROLOG: A new logic programming language with assumptions and abduction
- Christiansen, Dahl
- 2005
(Show Context)
Citation Context ...f [4], where the multiplicity of rule’s head appears in the exponent. Aware of this problem, CHR developers have built data structures to support efficient indexing on variables (attributed variables =-=[5]-=-) and ground data ⋆ Post-Doctoral Researcher of the Fund for Scientific Research - Flanders (Belgium) (F.W.O. - Vlaanderen)s4 Beata Sarna-Starosta and Tom Schrijvers (search trees [6]). With [7] came ... |

22 | Toward Probabilistic Constraint Handling Rules
- Frühwirth, Pierro, et al.
- 2001
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Citation Context ...aning that it is reintroduced in the Join-Body. This is because Cid1 should remain authorized even after a print job is submitted. Existing Join-Pattern implementations (eg. JoCaml [5], Polyphonic C# =-=[11]-=-) use a Join-Pattern compilation scheme [12] that maintains the states of JoinPatterns to determine when they can be triggered during runtime. (we briefly discuss this scheme in Section 3.1). Unfortun... |

19 | Dijkstra's algorithm with Fibonacci heaps: an executable description
- Sneyers, Schrijvers, et al.
- 2006
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Citation Context ... variables pending on its argument. We illustrate its use by an example; the curly brackets indicate the syntax for calling the constraint solver. Executing {X=Y+Z}, projecting assert(aux(p(X,Y,Z))). =-=(23)-=-s170 Henning Christiansen creates a clause equivalent with the following, aux(p(X,Y,Z)):- {X=Y+Z}. (24) Calling this predicate with new arguments can set up the relevant constraints. The modified rena... |

19 | On simplication of database integrity constraints
- Christiansen, Martinenghi
(Show Context)
Citation Context ...in specialized rules for each abducibles predicate. Simplification was suggested by [28] for database integrity checking; an unfolding of the theoretical foundations and a powerful method is given by =-=[29]-=-. We show here how this applies to the integrity checking shown in the code fragment (20) above. Typically simplification removes one order of magnitude (as in this example) or more. step explain([up(... |

10 |
Symbolic constraints for meta-logic programming
- Christiansen, Martinenghi
- 2000
(Show Context)
Citation Context ...g. CHR is a concurrent committed choice constraint programming language. Originally designed for writing constraint solvers, CHRs have through the years been exploited in a wide range of applications =-=[6, 7]-=-. A CHR program essentially consist of a set of multi-headed guarded rules, describing rewritings among multisets of constraints. These rewritings share a striking similarity with Join-Calculus and th... |

9 | The chrbased implementation of a system for generation and confirmation of hypotheses
- Alberti, Chesani, et al.
(Show Context)
Citation Context ...st goal of our approach, for multi-headed CHR rules, is to provide better constraint store indexes. Of course, our techniques benefit from the other effects as well. Symbol Indexing Structures In XSB =-=[18]-=- specialized trie-like structures store previously computed answer substitutions. These substitutions are indexed on their call patterns, and interpreted as partial structure indexes for subsumption-b... |

8 | Logic Grammars for Diagnosis and Repair
- Christiansen, Dahl
(Show Context)
Citation Context ...pported by CHR ∨,naf because it is not declarative. In order to allow this kind of reasoning we would need to employ some better-founded semantics for removal, like the one employed by Adaptive CHR ∨ =-=[4]-=-. – Complexity of Default Logics in CHR ∨ : As pointed out by [14], the problem of enumerating all the extensions for a Default Theory has an exponential time complexity. This is easily shown by the f... |

6 | On the implementation of global abduction
- Christiansen
(Show Context)
Citation Context ...starting from a given input have the same result and all successful ones have the same length. Note that if a program P is ∆H ωt (P)-deterministic for all input GH P , it is also observable confluent =-=[8]-=-. The notion of observable confluence does not require derivations to have the same length. 2.2 Deterministic Abstract CHR Machines We now define a class of CHR machines, which corresponds to the defi... |

6 |
Implementing probabilistic abductive logic programming with Constraint Handling Rules
- Christiansen
- 2008
(Show Context)
Citation Context ...rove performance, but rather makes it possible for the rules to be compiled at all. CHR Program Transformation We are not the first to consider program transformation in the context of CHR. Frühwirth =-=[22]-=- proposed the specialization of rules (rather than constraints) with respect to a given goal (rather than head matchings). Tacchella et al. [13] introduced a general technique for unfolding CHR rules ... |

6 | Source-to-source transformation for a class of expressive rules
- Frühwirth, Holzbaur
(Show Context)
Citation Context ...ue ; true), which means that a possible failure of test is absorbed, and the branch continue vanishes rather that provoking a failure in the execution of the CHR rules; this technique is also used in =-=[8, 24]-=-. Notice that when the arguments in the head of a clause are all variables, this is unnecessary as unification will always succeed. When a unification is performed, the auxiliary predicate recalculate... |

4 | Pre and post preferences over abductive models
- Pereira, Lopes, et al.
(Show Context)
Citation Context ...therwise guarded. The mains16 Beata Sarna-Starosta and Tom Schrijvers motivation for this limited expressivity is enabled compilation to a highly efficient finite-state automaton [20]. In recent work =-=[21]-=-, a flattening specialization similar to ours has been proposed to somewhat lift the severe expressivity restrictions. In this context, the flattening does not improve performance, but rather makes it... |

3 |
All’s well that ends well” - a proposal of global abduction
- Satoh
- 2004
(Show Context)
Citation Context ...t CHR algorithms with optimal complexity, which led to the use of hash tables for indexing ground data, and the general result that the complexity of CHR systems equals that of RAM machines [8]. CHRd =-=[9]-=- has slimmed the original indexing techniques based on attributed variables for faster evaluation of the class of direct-indexed CHR and use in a tabulated environment. In this paper we advance the re... |

2 |
CHR Grammars. Int’l Journal on Theory and Practice of Logic Programming 5(4-5
- Christiansen
- 2005
(Show Context)
Citation Context ...rative specification of constraint solvers, it is increasingly used for general purposes, in a wide range of applications. Efficient implementations exist for several host languages, including Prolog =-=[3, 4]-=-, Haskell, and Java [5]. An important, distinguishing feature of CHR are propagation rules. Unlike traditional rewrite rules, propagation rules do not remove the constraints matched by their head. The... |

2 |
An application of global abduction to an information agent which modifies a plan upon failure - preliminary report
- Satoh
- 2004
(Show Context)
Citation Context ... 43 First, we define some preliminary notions w.r.t. interpretations for constraints in CHR programs. These notions are adapted from the LP context [13–15]. Then, we introduce the existing approaches =-=[10, 11]-=-. T ermP and ConP denote the sets of respectively all terms and all constraints that can be constructed from the alphabet underlying P . As in LP, we wish to describe the constraints that participate ... |

2 |
recent version available at http://www.sics.se/isl
- Most
- 2006
(Show Context)
Citation Context ...dure significantly affects the complexity of rule evaluation, this source of expressiveness often leads to performance bottlenecks. This effect is borne out by the approximative complexity formula of =-=[4]-=-, where the multiplicity of rule’s head appears in the exponent. Aware of this problem, CHR developers have built data structures to support efficient indexing on variables (attributed variables [5]) ... |

1 |
Executable specifications for hypotheses-based reasoning with Prolog and Constraint Handling Rules
- Christiansen
(Show Context)
Citation Context ...red sets V1 and V2 exist: simply take V1 = delay varsP(c) and V2 = vars(c) \ V1. � In [10] the resulting semantics is shown to be correct with respect to the original refined operational semantics ωr =-=[7]-=-, where Solve is specified as: 1. Solve ⋆ 〈[b|A], S, B, T〉n ↣ P 〈S ++A, S, b ∧ B, T〉n where b is a built-in constraint and S ⊆ S such that vars(S \ S) ⊆ fixed(B). That is, all constraints with at leas... |

1 |
Holzbaur: OFAI clp(q,r) Manual, Edition 1.3.3
- Christian
- 1995
(Show Context)
Citation Context ...tional way to implement renaming without considering constraints is as follows, rename(X,Y):- assert(aux(X)),retract(aux(Y)). (22) We exemplify here for the clp(Q) constraint solver of SICStus Prolog =-=[25, 26]-=-, how the renaming can be extended properly. It includes a predicate projecting assert, which adds, in the body of a clause, the possible variables pending on its argument. We illustrate its use by an... |