Michael Maher | The University of New South Wales (original) (raw)

Papers by Michael Maher

… and Reasoning, 2002. …, 2002

Local search techniques have attracted considerable interest in the artificial intelligence (AI) ... more Local search techniques have attracted considerable interest in the artificial intelligence (AI) community since the development of GSAT (Selman et al., 1992) and the min-conflicts heuristic (Minton et al., 1992) for solving large propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively. Newer SAT techniques, such as the Discrete Langrangian Method (DLM)(Shang and Wah, 1998), have significantly improved on GSAT and can also be applied to general constraint satisfaction ...

Abstract: Defeasible logic is an efficient logic for defeasible reasoning. It is defined through ... more Abstract: Defeasible logic is an efficient logic for defeasible reasoning. It is defined through a proof theory and, until now, has had no model theory. In this paper a model-theoretic semantics is given for defeasible logic. The logic is sound and complete with respect to the semantics. We also briefly outline how this approach extends to a wide range of defeasible logics.

Abstract Local search techniques have attracted considerable interest in the artificial intellige... more Abstract Local search techniques have attracted considerable interest in the artificial intelligence (AI) community since the development of GSAT (Selman et al., 1992) and the min-conflicts heuristic (Minton et al., 1992) for solving large propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively.

Abstract Fair allocation of payoffs among cooperating players who can form various coalitions of ... more Abstract Fair allocation of payoffs among cooperating players who can form various coalitions of differing utilities is the classic game theoretic “coalition problem.” Shapley's value is perhaps the most famous fairness criterion. In this paper, a new allocation principle is proposed based on constraints. Initially constraints are defined by the coalition payoffs, in the standard way. The algorithm proceeds by “tightening” the constraints in a fair manner until the solution space is sufficiently small.

Abstract Local search techniques have attracted considerable interest in the artificial intellige... more Abstract Local search techniques have attracted considerable interest in the artificial intelligence community since the development of GSAT and the min-conflicts heuristic for solving propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively. Newer techniques, such as the discrete Langrangian method (DLM), have significantly improved on GSAT and can also be applied to general constraint satisfaction and optimization.

This paper proposes to specify semantic definitions for Prolog in terms of an oracle which provid... more This paper proposes to specify semantic definitions for Prolog in terms of an oracle which provides information on which clauses are to be applied to resolve a given goal. The approach is quite general. It is applicable to pure Prolog to define both operational and declarative semantics; and can be viewed as a basis for both sequential and parallel implementations.

Abstract We investigate the implication problem for constrained tuple-generating dependencies(CTG... more Abstract We investigate the implication problem for constrained tuple-generating dependencies(CTGDS), the extension of tupleand equality-generating dependencies that permits expression of semantic relations(constraints) on variables. The implication problem is central to identifying redundant integrity constraints, checking integrity constraints on constraint databases, detecting independence of queries and updates, and optimizing queries.

Abstract In this paper we explore abduction over the Herbrand domain-equations on the algebra of ... more Abstract In this paper we explore abduction over the Herbrand domain-equations on the algebra of finite terms (or finite trees)-which is a central element of logic programming and first-order automated reasoning. This paper is a case study of constraint abduction in the Herbrand domain. The direct relationship between Herbrand constraint abduction and type inference outlined above should make it easy to interpret the results of this paper in the context of type inference.

The problem of finding contained rewritings of queries using views is of great importance in medi... more The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context.

We address the problem of representing sets of rational trees, using methods from the eld of Non-... more We address the problem of representing sets of rational trees, using methods from the eld of Non-Monotonic Reasoning. The representation of sets of rational trees is relevant to type systems for many Prologs (which use unication without the\ occur check") and for more conventional languages with pointer-based data structures 18]. The basis of our representation languages is a class of set constraints (see, for example, 7]).

The problem of finding contained rewritings of queries using views is of great importance in medi... more The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context.

We address the problem of computing and representing answers of constraint abduction problems ove... more We address the problem of computing and representing answers of constraint abduction problems over the Herbrand domain. This problem is of interest when performing type inference involving generalized algebraic data types. We show that simply recognizing a maximally general answer or fully maximal answer is co-NP complete. However we present an algorithm that computes the (finite) set of fully maximal answers of an abduction problem.

The simplicity and elegance of definite clauses makes this formalism attractive from a theoretica... more The simplicity and elegance of definite clauses makes this formalism attractive from a theoretical point of view. The objects in this formalism are the uninterpreted terms over the Herbrand universe. Programming however is not done exclusively in the Herbrand universe, but uses higher level concepts such as arithmetic. In that sense we can view definite clauses as the Turing machines of Logic Programming. This gap between theory and programming practice can be reduced by introducing user-oriented domains into the formalism.

What may cause some confusion in the present example is a feeling one might have that antimilitar... more What may cause some confusion in the present example is a feeling one might have that antimilitary and paci st are the same. Not eveybody agrees on this (not even the authors among themselves!) but if it helps, replace" antimilitary" by another predicate semantically unrelated to all the others.

Defeasible logic is a logic-programming based nonmonotonic reasoning formalism which has an effic... more Defeasible logic is a logic-programming based nonmonotonic reasoning formalism which has an efficient implementation. It makes use of facts, strict rules, defeasible rules, defeaters, and a superiority relation. We clarify the proof theory of defeasible logic through an analysis of the conclusions it can draw. Using it, we show that defeaters do not add to the expressiveness of defeasible logic, among other results. The analysis also supports the restriction of defeasible logic to admit only acyclic superiority relations.

Abstract. We address a global constraint for enforcing contiguity. Contiguity is the property tha... more Abstract. We address a global constraint for enforcing contiguity. Contiguity is the property that all of one kind of object in an array or list are grouped together; it is a one-dimensional discrete form of convexity. We present an implementation of this property in a concurrent constraint programming language. We adapt and apply the constraint propagation framework of [19] to analyse the contiguity property.

Abstract We introduce parameterized substitutions, and give them a semantics as sets of valuation... more Abstract We introduce parameterized substitutions, and give them a semantics as sets of valuations. It has been shown (Eder 85) that the (unparameterized) idempotent substitutions (modulo an appropriate equivalence relation) form a complete Noetherian lattice under the “more general than” ordering. However this result does not extend to all substitutions. We show that the set of all parameterized substitutions (again modulo an equivalence) forms a complete Noetherian lattice.

We address the problem of determining those constraint domains A for which the traditional logic ... more We address the problem of determining those constraint domains A for which the traditional logic programming semantics and the constraint logic programming semantics CLP (A) coincide. This reduces to a study of non-standard models of Clark's axioms and the notion of solution compactness introduced in the CLP scheme.

We develop a framework for addressing correctness and time-liness-of-propagation issues for react... more We develop a framework for addressing correctness and time-liness-of-propagation issues for reactive constraints—global constraints or user-defined constraints that are implemented through constraint propagation. The notion of propagation completeness is introduced to capture timeliness of constraint propagation. A generalized form of arc-consistency is formulated which unifies many local consistency conditions in the literature.

We propose new filtering algorithms for the Sequence constraint and some extensions of the Sequen... more We propose new filtering algorithms for the Sequence constraint and some extensions of the Sequence constraint based on network flows. We enforce domain consistency on the Sequence constraint in O (n 2) time down a branch of the search tree. This improves upon the best existing domain consistency algorithm by a factor of O (logn). The flows used in these algorithms are derived from a linear program.

… and Reasoning, 2002. …, 2002

Local search techniques have attracted considerable interest in the artificial intelligence (AI) ... more Local search techniques have attracted considerable interest in the artificial intelligence (AI) community since the development of GSAT (Selman et al., 1992) and the min-conflicts heuristic (Minton et al., 1992) for solving large propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively. Newer SAT techniques, such as the Discrete Langrangian Method (DLM)(Shang and Wah, 1998), have significantly improved on GSAT and can also be applied to general constraint satisfaction ...

Abstract: Defeasible logic is an efficient logic for defeasible reasoning. It is defined through ... more Abstract: Defeasible logic is an efficient logic for defeasible reasoning. It is defined through a proof theory and, until now, has had no model theory. In this paper a model-theoretic semantics is given for defeasible logic. The logic is sound and complete with respect to the semantics. We also briefly outline how this approach extends to a wide range of defeasible logics.

Abstract Local search techniques have attracted considerable interest in the artificial intellige... more Abstract Local search techniques have attracted considerable interest in the artificial intelligence (AI) community since the development of GSAT (Selman et al., 1992) and the min-conflicts heuristic (Minton et al., 1992) for solving large propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively.

Abstract Fair allocation of payoffs among cooperating players who can form various coalitions of ... more Abstract Fair allocation of payoffs among cooperating players who can form various coalitions of differing utilities is the classic game theoretic “coalition problem.” Shapley's value is perhaps the most famous fairness criterion. In this paper, a new allocation principle is proposed based on constraints. Initially constraints are defined by the coalition payoffs, in the standard way. The algorithm proceeds by “tightening” the constraints in a fair manner until the solution space is sufficiently small.

Abstract Local search techniques have attracted considerable interest in the artificial intellige... more Abstract Local search techniques have attracted considerable interest in the artificial intelligence community since the development of GSAT and the min-conflicts heuristic for solving propositional satisfiability (SAT) problems and binary constraint satisfaction problems (CSPs) respectively. Newer techniques, such as the discrete Langrangian method (DLM), have significantly improved on GSAT and can also be applied to general constraint satisfaction and optimization.

This paper proposes to specify semantic definitions for Prolog in terms of an oracle which provid... more This paper proposes to specify semantic definitions for Prolog in terms of an oracle which provides information on which clauses are to be applied to resolve a given goal. The approach is quite general. It is applicable to pure Prolog to define both operational and declarative semantics; and can be viewed as a basis for both sequential and parallel implementations.

Abstract We investigate the implication problem for constrained tuple-generating dependencies(CTG... more Abstract We investigate the implication problem for constrained tuple-generating dependencies(CTGDS), the extension of tupleand equality-generating dependencies that permits expression of semantic relations(constraints) on variables. The implication problem is central to identifying redundant integrity constraints, checking integrity constraints on constraint databases, detecting independence of queries and updates, and optimizing queries.

Abstract In this paper we explore abduction over the Herbrand domain-equations on the algebra of ... more Abstract In this paper we explore abduction over the Herbrand domain-equations on the algebra of finite terms (or finite trees)-which is a central element of logic programming and first-order automated reasoning. This paper is a case study of constraint abduction in the Herbrand domain. The direct relationship between Herbrand constraint abduction and type inference outlined above should make it easy to interpret the results of this paper in the context of type inference.

The problem of finding contained rewritings of queries using views is of great importance in medi... more The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context.

We address the problem of representing sets of rational trees, using methods from the eld of Non-... more We address the problem of representing sets of rational trees, using methods from the eld of Non-Monotonic Reasoning. The representation of sets of rational trees is relevant to type systems for many Prologs (which use unication without the\ occur check") and for more conventional languages with pointer-based data structures 18]. The basis of our representation languages is a class of set constraints (see, for example, 7]).

The problem of finding contained rewritings of queries using views is of great importance in medi... more The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context.

We address the problem of computing and representing answers of constraint abduction problems ove... more We address the problem of computing and representing answers of constraint abduction problems over the Herbrand domain. This problem is of interest when performing type inference involving generalized algebraic data types. We show that simply recognizing a maximally general answer or fully maximal answer is co-NP complete. However we present an algorithm that computes the (finite) set of fully maximal answers of an abduction problem.

The simplicity and elegance of definite clauses makes this formalism attractive from a theoretica... more The simplicity and elegance of definite clauses makes this formalism attractive from a theoretical point of view. The objects in this formalism are the uninterpreted terms over the Herbrand universe. Programming however is not done exclusively in the Herbrand universe, but uses higher level concepts such as arithmetic. In that sense we can view definite clauses as the Turing machines of Logic Programming. This gap between theory and programming practice can be reduced by introducing user-oriented domains into the formalism.

What may cause some confusion in the present example is a feeling one might have that antimilitar... more What may cause some confusion in the present example is a feeling one might have that antimilitary and paci st are the same. Not eveybody agrees on this (not even the authors among themselves!) but if it helps, replace" antimilitary" by another predicate semantically unrelated to all the others.

Defeasible logic is a logic-programming based nonmonotonic reasoning formalism which has an effic... more Defeasible logic is a logic-programming based nonmonotonic reasoning formalism which has an efficient implementation. It makes use of facts, strict rules, defeasible rules, defeaters, and a superiority relation. We clarify the proof theory of defeasible logic through an analysis of the conclusions it can draw. Using it, we show that defeaters do not add to the expressiveness of defeasible logic, among other results. The analysis also supports the restriction of defeasible logic to admit only acyclic superiority relations.

Abstract. We address a global constraint for enforcing contiguity. Contiguity is the property tha... more Abstract. We address a global constraint for enforcing contiguity. Contiguity is the property that all of one kind of object in an array or list are grouped together; it is a one-dimensional discrete form of convexity. We present an implementation of this property in a concurrent constraint programming language. We adapt and apply the constraint propagation framework of [19] to analyse the contiguity property.

Abstract We introduce parameterized substitutions, and give them a semantics as sets of valuation... more Abstract We introduce parameterized substitutions, and give them a semantics as sets of valuations. It has been shown (Eder 85) that the (unparameterized) idempotent substitutions (modulo an appropriate equivalence relation) form a complete Noetherian lattice under the “more general than” ordering. However this result does not extend to all substitutions. We show that the set of all parameterized substitutions (again modulo an equivalence) forms a complete Noetherian lattice.

We address the problem of determining those constraint domains A for which the traditional logic ... more We address the problem of determining those constraint domains A for which the traditional logic programming semantics and the constraint logic programming semantics CLP (A) coincide. This reduces to a study of non-standard models of Clark's axioms and the notion of solution compactness introduced in the CLP scheme.

We develop a framework for addressing correctness and time-liness-of-propagation issues for react... more We develop a framework for addressing correctness and time-liness-of-propagation issues for reactive constraints—global constraints or user-defined constraints that are implemented through constraint propagation. The notion of propagation completeness is introduced to capture timeliness of constraint propagation. A generalized form of arc-consistency is formulated which unifies many local consistency conditions in the literature.

We propose new filtering algorithms for the Sequence constraint and some extensions of the Sequen... more We propose new filtering algorithms for the Sequence constraint and some extensions of the Sequence constraint based on network flows. We enforce domain consistency on the Sequence constraint in O (n 2) time down a branch of the search tree. This improves upon the best existing domain consistency algorithm by a factor of O (logn). The flows used in these algorithms are derived from a linear program.