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Theory and Practice of Constraint Handling Rules
, 1998
"... Constraint Handling Rules (CHR) are our proposal to allow more flexibility and applicationoriented customization of constraint systems. CHR are a declarative language extension especially designed for writing userdefined constraints. CHR are essentially a committedchoice language consisting of mu ..."
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Cited by 462 (36 self)
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Constraint Handling Rules (CHR) are our proposal to allow more flexibility and applicationoriented customization of constraint systems. CHR are a declarative language extension especially designed for writing userdefined constraints. CHR are essentially a committedchoice language consisting of multiheaded guarded rules that rewrite constraints into simpler ones until they are solved. In this broad survey we aim at covering all aspects of CHR as they currently present themselves. Going from theory to practice, we will define syntax and semantics for CHR, introduce an important decidable property, confluence, of CHR programs and define a tight integration of CHR with constraint logic programming languages. This survey then describes implementations of the language before we review several constraint solvers  both traditional and non standard ones  written in the CHR language. Finally we introduce two innovative applications that benefited from using CHR.
The Oz Programming Model
 COMPUTER SCIENCE TODAY, LECTURE NOTES IN COMPUTER SCIENCE
, 1995
"... The Oz Programming Model (OPM) is a concurrent programming model subsuming higherorder functional and objectoriented programming as facets of a general model. This is particularly interesting for concurrent objectoriented programming, for which no comprehensive formal model existed until now. ..."
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Cited by 315 (11 self)
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The Oz Programming Model (OPM) is a concurrent programming model subsuming higherorder functional and objectoriented programming as facets of a general model. This is particularly interesting for concurrent objectoriented programming, for which no comprehensive formal model existed until now. The model
A Foundation for Higherorder Concurrent Constraint Programming
, 1994
"... We present the flcalculus, a computational calculus for higherorder concurrent programming. The calculus can elegantly express higherorder functions (both eager and lazy) and concurrent objects with encapsulated state and multiple inheritance. The primitives of the flcalculus are logic variables ..."
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Cited by 66 (13 self)
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We present the flcalculus, a computational calculus for higherorder concurrent programming. The calculus can elegantly express higherorder functions (both eager and lazy) and concurrent objects with encapsulated state and multiple inheritance. The primitives of the flcalculus are logic variables, names, procedural abstraction, and cells. Cells provide a notion of state that is fully compatible with concurrency and constraints. Although it does not have a dedicated communication primitive, the flcalculus can elegantly express onetomany and manytoone communication. There is an interesting relationship between the flcalculus and the ßcalculus: The flcalculus is subsumed by a calculus obtained by extending the asynchronous and polyadic ßcalculus with logic variables. The flcalculus can be extended with primitives providing for constraintbased problem solving in the style of logic programming. A such extended flcalculus has the remarkable property that it combines firstor...
ObjectOriented Concurrent Constraint Programming in Oz
, 1993
"... Oz is a higherorder concurrent constraint programming system under development at DFKI. It combines ideas from logic and concurrent programming in a simple yet expressive language. From logic programming Oz inherits logic variables and logic data structures, which provide for a programming style wh ..."
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Cited by 60 (16 self)
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Oz is a higherorder concurrent constraint programming system under development at DFKI. It combines ideas from logic and concurrent programming in a simple yet expressive language. From logic programming Oz inherits logic variables and logic data structures, which provide for a programming style where partial information about the values of variables is imposed concurrently and incrementally. A novel feature of Oz is the support of higherorder programming without sacrificing that denotation and equality of variables are captured by firstorder logic. Another new feature of Oz are cells, a concurrent construct providing a minimal form of state fully compatible with logic data structures. These two features allow to express objects as procedures with state, avoiding the problems of stream communication, the conventional communication mechanism employed in concurrent logic programming. Based on cells and higherorder programming, Oz readily supports concurrent objectoriented programming including object identity, late method binding, multiple inheritance, "self", "super", batches, synchronous and asynchronous communication.
Oz Explorer: A Visual Constraint Programming Tool
, 1997
"... This paper describes the Oz Explorer and its implementation. The Explorer is a visual constraint programming tool intended to support the development of constraint programs. It uses the search tree of a constraint problem as its central metaphor. Exploration and visualization of the search tree ar ..."
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Cited by 55 (1 self)
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This paper describes the Oz Explorer and its implementation. The Explorer is a visual constraint programming tool intended to support the development of constraint programs. It uses the search tree of a constraint problem as its central metaphor. Exploration and visualization of the search tree are userdriven and interactive. The constraints of any node in the tree are available firstclass: predefined or userdefined procedures can be used to display or analyze them. The Explorer is a fast and memory efficient tool intended for the development of realworld constraint programs. The Explorer is implemented in Oz using firstclass computation spaces. There is no fixed search strategy in Oz. Instead, firstclass computation spaces allow to program search engines. The Explorer is one particular example of a userguided search engine. The use of recomputation to trade space for time makes it possible to solve large realworld problems, which would use too much memory otherwise.
FiniteTree Analysis for Constraint LogicBased Languages: The Complete Unabridged Version
, 2001
"... Logic languages based on the theory of rational, possibly infinite, trees have much appeal in that rational trees allow for faster unification (due to the safe omission of the occurscheck) and increased expressivity (cyclic terms can provide very efficient representations of grammars and other usef ..."
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Cited by 46 (16 self)
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Logic languages based on the theory of rational, possibly infinite, trees have much appeal in that rational trees allow for faster unification (due to the safe omission of the occurscheck) and increased expressivity (cyclic terms can provide very efficient representations of grammars and other useful objects). Unfortunately, the use of infinite rational trees has problems. For instance, many of the builtin and library predicates are illdefined for such trees and need to be supplemented by runtime checks whose cost may be significant. Moreover, some widelyused program analysis and manipulation techniques are correct only for those parts of programs working over finite trees. It is thus important to obtain, automatically, a knowledge of the program variables (the finite variables) that, at the program points of interest, will always be bound to finite terms. For these reasons, we propose here a new dataflow analysis, based on abstract interpretation, that captures such information. We present a parametric domain where a simple component for recording finite variables is coupled, in the style of the open product construction of Cortesi et al., with a generic domain (the parameter of the construction) providing sharing information. The sharing domain is abstractly specified so as to guarantee the correctness of the combined domain and the generality of the approach. This finitetree analysis domain is further enhanced by coupling it with a domain of Boolean functions, called finitetree dependencies, that precisely captures how the finiteness of some variables influences the finiteness of other variables. We also summarize our experimental results showing how finitetree analysis, enhanced with finitetree dependencies, is a practical means of obtaining precise finitenes...
An Efficient Graph Algorithm for Dominance Constraints
 JOURNAL OF ALGORITHMS
, 2003
"... Dominance constraints are logical descriptions of trees that are widely used in computational linguistics. Their general satisfiability problem is known to be NPcomplete. Here we identify normal dominance constraints and present an efficient graph algorithm for testing their satisfiablity in dete ..."
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Cited by 44 (18 self)
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Dominance constraints are logical descriptions of trees that are widely used in computational linguistics. Their general satisfiability problem is known to be NPcomplete. Here we identify normal dominance constraints and present an efficient graph algorithm for testing their satisfiablity in deterministic polynomial time. Previously, no polynomial time algorithm was known.
Oz  A Programming Language for MultiAgent Systems
 In 13th International Joint Conference on Artificial Intelligence
, 1993
"... Oz is an experimental higherorder concurrent constraint programming system under development at DFKI. It combines ideas from logic and concurrent programming in a simple yet expressive language. From logic programming Oz inherits logic variables and logic data structures, which provide for a ..."
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Cited by 38 (7 self)
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Oz is an experimental higherorder concurrent constraint programming system under development at DFKI. It combines ideas from logic and concurrent programming in a simple yet expressive language. From logic programming Oz inherits logic variables and logic data structures, which provide for a programming style where partial information about the values of variables is imposed concurrently and incrementally. A novel feature of Oz is that it accommodates higherorder programming without sacrificing that denotation and equality of variables are captured by firstorder logic. Another new feature of Oz is constraint communication, a new form of asynchronous communication exploiting logic variables. Constraint communication avoids the problems of stream communication, the conventional communication mechanism employed in concurrent logic programming. Constraint communication can be seen as providing a minimal form of state fully compatible with logic data structures. Bas...
An Improved Lower Bound for the Elementary Theories of Trees
, 1996
"... . The firstorder theories of finite and rational, constructor and feature trees possess complete axiomatizations and are decidable by quantifier elimination [15, 13, 14, 5, 10, 3, 20, 4, 2]. By using the uniform inseparability lower bounds techniques due to Compton and Henson [6], based on repr ..."
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Cited by 29 (3 self)
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. The firstorder theories of finite and rational, constructor and feature trees possess complete axiomatizations and are decidable by quantifier elimination [15, 13, 14, 5, 10, 3, 20, 4, 2]. By using the uniform inseparability lower bounds techniques due to Compton and Henson [6], based on representing large binary relations by means of short formulas manipulating with high trees, we prove that all the above theories, as well as all their subtheories, are nonelementary in the sense of Kalmar, i.e., cannot be decided within time bounded by a k story exponential function 1 exp k (n) for any fixed k. Moreover, for some constant d ? 0 these decision problems require nondeterministic time exceeding exp 1 (bdnc) infinitely often. 1 Introduction Trees are fundamental in Computer Science. Different tree structures are used as underlying domains in automated theorem proving, term rewriting, functional and logic programming, constraint solving, symbolic computation, knowledge re...