Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-01-02a, Department of Computer Science and Engineering, University of Washington, May 1993  Home/Search   Document Not in Database   Summary   Related Articles   Check

....a local comparator, two solutions that are incomparable at strong levels may still be compared at weaker levels. The constraint hierarchies are used in Hierarchical Constraint Logic Programming (HCLP) which is an extension of Constraint Logic Programming (CLP) In the original definition of HCLP [4,14] only alternate solutions to one constraint hierarchy are compared and the best solutions are returned. The later extension of HCLP [13] also enables comparison of solutions to more constraint hierarchies arising from different choices of rules in HCLP program. Such comparison, called ....

Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-01-02a, Department of Computer Science and Engineering, University of Washington, May 1993

....be used for inter hierarchy comparison [13] i.e. comparison of solutions to two or more constraint hierarchies. The constraint hierarchies are used in Hierarchical Constraint Logic Programming (HCLP) which is an extension of Constraint Logic Programming (CLP) In the original definiton of HCLP [4,14] only alternate solutions to one constraint hierarchy are compared and the best solutions are returned. The later extension of HCLP [13] also enables comparison of solutions to more constraint hierarchies arising from different choices of rules in HCLP program. Such comparison, called ....

....g(q,H i ) g(s,H i ) g(q,H k ) g(s,H k ) Note that the scheme of globally better comparator is parameterized by the combining function g that combines errors of individual constraints via, e.g. weighted sum, worst case or least squares methods. 3 Recent definition of constraint hierarchies [14] also supports another type of comparator called regionally better. 4 Constraint hierarchies extend the Constraint Logic Programming CLP(R) scheme parameterized by the domain R of constraints into a more general scheme Hierarchical Constraint Logic Programming HCLP(R,C) parameterized by the ....

Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-0102a, Department of Computer Science and Engineering, University of Washington, May 1993

....problem speci cations that are unsolvable. However, a solution in the form of a layout, plan, schedule, etc. has to be generated. One way of solving this con ict is to introduce constraint hierarchies. Their formal foundations and their embedding in constraint logic programming are presented in [1, 14, 15]. Constraint hierarchies consist of required (hard) constraints that must be satis ed, and non required (soft) constraints that must only be satis ed as far as possible. For constraint hierarchies based on the trivial error function that returns 0 if the considered constraint is satis ed and 1 if ....

....the weights w 1 ; w k are nonnegative numbers. Together with the error function e, the binary relations g = and g , these error combining functions result in the global comparators worstcase metric better, weighted sum metric better and least squares metric better, respectively [14]. 5 An Incremental But Non Adaptive Solution Process In [17] a solution process for the considered constraint hierarchies is de ned. Its two main steps are recapitulated. 5.1 The Transformation to Simpler Hierarchies No matter which global comparator is chosen, the idea is to represent the ....

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Molly Ann Wilson. Hierarchical Constraint Logic Programming. PhD thesis, Department of Computer Science and Engineering, University of Washington, 1993.

....201 96 0197. 2 1. INTRODUCTION Constraint hierarchy is a method for describing over constrained systems of constraints by specifying constraints with hierarchical strengths or preferences 2 . Constraint hierarchies are widely used in areas like HCLP (Hierarchical Constraint Logic Programming) [4, 21], CIP (Constraint Imperative Programming) 8] and graphical user interfaces construction [5] The major advantage of constraint hierarchies is their declarative expression of preferences or strengths of constraints rather than encoding them in the procedural parts of the language. In a constraint ....

....of constraints with the same strength by applying, e.g. weighted sum, least squares or similar methods. For purposes of the introduction to constraint hierarchies we will use the former definition of constraint hierarchies [4] which is simpler but also a bit different from the newer definition [21]. A constraint is a relation over some domain D. The domain D determines the constraint predicate symbols PD of the language, which must include = A constraint is thus an expression of the form p(t 1 , t n ) where p is an n ary symbol in PD and each t i is a term. A labeled constraint is a ....

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Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-0102a, Department of Computer Science and Engineering, University of Washington, May 1993

....8 4 1. INTRODUCTION Constraint hierarchies were introduced for describing over constrained systems of constraints by specifying constraints with hierarchical strengths or preferences 1 . Constraint hierarchies are widely used in areas like HCLP (Hierarchical Constraint Logic Programming) [9, 25] an extension of CLP (Constraint Logic Programming) 15] to include constraint hierarchies, CIP (Constraint Imperative Programming) 16] an integration of declarative constraint programming and imperative object oriented programming, and graphical user interfaces construction [8] The major ....

....weighted sum, least squares or similar methods. For purposes of the introduction to constraint hierarchies we prefer the earlier definition of constraint hierarchies [9] which is simpler but also a bit different (e.g. it does not support regionally better comparators) to more recent definition [25]. A constraint is a relation over some domain D. The domain D determines the constraint predicate symbols PD of the language. A constraint is thus an expression of the form p(t 1 , t n ) where p is an n ary symbol in PD and each t i is a term. A labeled constraint is a constraint labeled with a ....

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Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-0102a, Department of Computer Science and Engineering, University of Washington, May 1993

....2 1. INTRODUCTION Constraint hierarchies were introduced for describing over constrained systems of constraints by specifying constraints with hierarchical strengths or preferences 2 . Constraint hierarchies are widely used in areas like HCLP (Hierarchical Constraint Logic Programming) [8, 23] an extension of CLP (Constraint Logic Programming) 13] to include constraint hierarchies, CIP (Constraint Imperative Programming) 14] an integration of declarative constraint programming and imperative object oriented programming, and graphical user interfaces construction [7] The major ....

....least squares or similar methods. For purposes of the introduction to constraint hierarchies we will use the former definition of constraint hierarchies [8] which is simpler but also a bit different (e.g. it does not support regionally better comparators) from the more recent definition [23]. A constraint is a relation over some domain D. The domain D determines the constraint predicate symbols PD of the language. A constraint is thus an expression of the form p(t 1 , t n ) where p is an n ary symbol in PD and each t i is a term. A labeled constraint is a constraint labeled ....

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Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-0102a, Department of Computer Science and Engineering, University of Washington, May 1993

....extensions have not been drawn up yet for extendible meta interpreters. So, it is the first open area of conceivable research. The second area of interest is using techniques of extendible meta interpreters in the construction of HCLP (Hierarchical Constraint Logic Programming) interpreters [18]. Inspired by the meta terms and attributed variables [9] we suggest to use extendible meta interpreters in a similar manner [5] While the meta terms generalize the process of unification and they are suitable for implementing CLP interpreters therefore, extendible meta interpreters generalize ....

Wilson, M., Borning, A., Hierarchical Constraint Logic Programming, TR 93-01-02a, Department of Computer Science and Engineering, University of Washington, May 1993

....problem, we introduce composite constraints into (PO )HCLP. We present the formal syntax and semantics of PO HCLP, and establish its soundness and completeness results. A prototype of PO HCLP(R,WSPB) is constructed using CLP(R) 1 Introduction Hierarchical Constraint Logic Programming (HCLP) [15, 16] extends the CLP scheme [8] by including non required constraints (or soft constraints) so that overconstrained problems can be modeled more declaratively in this extended framework. HCLP, however, suffers from two limitations. First, constraints are classified into different levels according to ....

....section provides the theoretical background to this paper. We first outline such important concepts as combining functions and comparators in the constraint hierarchy theory. The hierarchical constraint logic programming (HCLP) framework is then presented. Interested readers may refer to [1] and [15] for details. 3.1 Constraint Hierarchies A constraint hierarchy is a collection of constraints, each of which is associated with a label for stating its strength. The strength labels are totally ordered . According to the associated labels, constraints are classified into different disjoint ....

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M.A. Wilson. Hierarchical Constraint Logic Programming. PhD thesis, Department of Computer Science and Engineering, University of Washington, 1993.

.... researchers have developed several general purpose languages that use constraints, including Bertrand [30] Kaleidoscope [14, 18] Siri [23, 24] as well as a number of languages integrating constraints with logic programming including CAL [42] CHIP [9, 46] CLP(R) 27, 28] CLP(6 ) 48] HCLP(R) [6, 49], Prolog III [8] and the cc (concurrent constraint) languages [41, 40] 2.1 Refinement versus Perturbation We can roughly classify constraint based languages and systems as using one of two approaches: the refinement model or the perturbation model. In both cases constraints restrict the values ....

....and removing constraints in any order. Constraint based logic programming languages typically only allow removing constraints during backtracking. Neither of these problems is insurmountable, however, and some work has been done on implementing user interfaces in systems using the refinement model [49]. 2.2 Constraint Hierarchies For constraint systems that are restricted to non circular, one way constraints, when a variable value is perturbed, it is clear how to compute new values for the variables so that all the constraints are again satisfied. However, if the constraints are multi way, or ....

Molly Wilson. Hierarchical Constraint Logic Programming. PhD thesis, Department of Computer Science and Engineering, University of Washington, 1993. Forthcoming.

....In order to handle this problem, where not all constraints of the grammar can be satisfied in parsing a sentence, future constraint based linguistic processing will require dynamic and preferential constraint satisfaction. Thus research in areas such as hierarchical constraint logic programming [ Wilson and Borning, 1993 ] has potential applications for such NLP tasks. HCLP can be thought as an extension of the CLP(X) paradigm to CLP(X,S) where X represents the constraint domain and S represents the comparator or selection function that can handle preferences in case of conflicts. 3 Requirements of NLP for a ....

Molly Wilson and Alan Borning. Hierarchical constraint logic programming. Technical Report 93-01-02a, Department of Computer Science and Engineering, University of Washington, May 1993.

....in S must be such that, after its application, all the required constraints hold. In addition, each valuation in S has to satisfy the nonrequired constraints as well as possible, respecting their relative strengths. Thus, several comparators and error functions are defined in Wilson s thesis [WIL 92] to selecting the non required constraints. For inequality constraint the error functions must be minimized. So, locallymetric better comparator is used in ORANOS constraints solver. For a formal definition, the reader should refer to the previous reference) Satisfied Constraint : a ....

Wilson M., Hierarchical Constraint Logic Programming , PhD thesis, Department of Computer Science and Engineering, University of Washington, 1992.

....In order to handle this problem, where not all constraints of the grammar can be satisfied in parsing a sentence, future constraint based linguistic processing will require dynamic and preferential constraint satisfaction. Thus research in areas such as hierarchical constraint logic programming [ Wilson and Borning, 1993 ] has potential applications for such NLP tasks. HCLP can be thought as an extension of the CLP(X) paradigm to CLP(X,S) where X represents the constraint domain and S represents the comparator or selection function that can handle preferences in case of conflicts. 3.4.2 Relationship between Logic ....

M. Wilson and A. Borning. Hierarchical constraint logic programming. Technical Report 93-01-02a, Department of Computer Science and Engineering, University of Washington, May 1993.

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