Results 1  10
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23
Interaction between Path and Type Constraints
 In Proceedings of ACM Symposium on Principles of Database Systems (PODS
, 1999
"... This paper investigates that interaction. In particular it studies constraint implication problems, which are important both in understanding the semantics of type/constraint systems and in query optimization. It shows that path constraints interact with types in a highly intricate way. For that pur ..."
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Cited by 35 (15 self)
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This paper investigates that interaction. In particular it studies constraint implication problems, which are important both in understanding the semantics of type/constraint systems and in query optimization. It shows that path constraints interact with types in a highly intricate way. For that purpose a number of results on path constraint implication are established in the presence and absence of type systems. These results demonstrate that adding a type system may in some cases simplify reasoning about path constraints and in other cases make it harder. For example, it is shown that there is a path constraint implication problem that is decidable in PTIME in the untyped context, but that becomes undecidable when a type system is added. On the other hand, there is an implication problem that is undecidable in the untyped context, but becomes not only decidable in cubic time but also finitely axiomatizable when a type system is imposed
A Modal Perspective on Path Constraints
, 2003
"... We analyze several classes of path constraints for semistructured data and prove a umber of decidability and complexity results for such constraints. While some of our decidability results were known before, we believe that our improved complexity bounds are new. Our proofs are based on technique ..."
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Cited by 24 (0 self)
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We analyze several classes of path constraints for semistructured data and prove a umber of decidability and complexity results for such constraints. While some of our decidability results were known before, we believe that our improved complexity bounds are new. Our proofs are based on techniques from modal logic and automata theory. We believe that our modal logic perspective sheds additional light on the reasons for previously known decidability and complexity results.
The FirstOrder Theory of Ordering Constraints over Feature Trees
 Discrete Mathematics and Theoretical Computer Science
, 2001
"... The system FT of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. We investigate the firstorder theory of FT and its fragments, both over finite trees and over possibly infinite trees. We prove that the firstor ..."
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Cited by 19 (5 self)
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The system FT of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. We investigate the firstorder theory of FT and its fragments, both over finite trees and over possibly infinite trees. We prove that the firstorder theory of FT is undecidable, in contrast to the firstorder theory of FT which is wellknown to be decidable. We determine the complexity of the entailment problem of FT with existential quantification to be PSPACEcomplete, by proving its equivalence to the inclusion problem of nondeterministic finite automata. Our reduction from the entailment problem to the inclusion problem is based on a new alogrithm that, given an existential formula of FT , computes a finite automaton which accepts all its logic consequences.
Query Optimization for Semistructured Data Using Path Constraints in a Deterministic Data Model
 In Proceedings of International Workshop on Database Programming Languages (DBPL
, 1999
"... . Path constraints have been studied for semistructured data modeled as a rooted edgelabeled directed graph [4, 1113]. In this model, the implication problems associated with many natural path constraints are undecidable [11, 13]. A variant of the graph model, called the deterministic data mo ..."
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Cited by 18 (8 self)
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. Path constraints have been studied for semistructured data modeled as a rooted edgelabeled directed graph [4, 1113]. In this model, the implication problems associated with many natural path constraints are undecidable [11, 13]. A variant of the graph model, called the deterministic data model , was recently proposed in [10]. In this model, data is represented as a graph with deterministic edge relations, i.e., the edges emanating from any node in the graph have distinct labels. This model is more appropriate for representing, e.g., ACeDB [27] databases and Web sites. This paper investigates path constraints for the deterministic data model. It demonstrates the application of path constraints to, among others, query optimization. Three classes of path constraints are considered: the language Pc introduced in [11], an extension of Pc , denoted by P w c , by including wildcards in path expressions, and a generalization of P w c , denoted by P c , by representing pa...
Ordering Constraints over Feature Trees
, 1999
"... Feature trees are the formal basis for algorithms manipulating record like structures in constraint programming, computational linguistics and in concrete applications like software configuration management. Feature trees model records, and constraints over feature trees yield extensible and modular ..."
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Cited by 14 (5 self)
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Feature trees are the formal basis for algorithms manipulating record like structures in constraint programming, computational linguistics and in concrete applications like software configuration management. Feature trees model records, and constraints over feature trees yield extensible and modular record descriptions. We introduce the constraint system FT of ordering constraints interpreted over feature trees. Under the view that feature trees represent symbolic information, the relation corresponds to the information ordering ("carries less information than"). We present two algorithms in cubic time, one for the satisfiability problem and one for the entailment problem of FT . We show that FT has the independence property. We are thus able to handle negative conjuncts via entailment and obtain a cubic algorithm that decides the satisfiability of conjunctions of positive and negated ordering constraints over feature trees. Furthermore, we reduce the satisfiability problem of Dorre's weak subsumption constraints to the satisfiability problem of FT and improve the complexity bound for solving weak subsumption constraints from O(n^5) to O(n³).
Simulating without Negation
, 1997
"... Although negationfree languages are widely used in logic and computer science, relatively little is known about their expressive power. To address this issue we consider kinds of nonsymmetric bisimulations called directed simulations, and use these to analyse the expressive power and model theory ..."
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Cited by 12 (4 self)
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Although negationfree languages are widely used in logic and computer science, relatively little is known about their expressive power. To address this issue we consider kinds of nonsymmetric bisimulations called directed simulations, and use these to analyse the expressive power and model theory of negationfree modal and temporal languages. We first use them to obtain preservation, safety and definability results for a simple negationfree modal language. We then obtain analogous results for stronger negationfree languages. Finally, we extend our methods to deal with languages with nonBoolean negation. Keywords: Expressive power, modal logic, negationfree languages. 1
Path Constraints from a Modal Logic Point of View (Extended Abstract)
 In 8th International Workshop on Knowledge Representation meets Databases (KRDB2001
, 2001
"... We analyze several classes of path constraints for semistructured data in a uni ed framework and prove some decidability and complexity results for these constraints by embedding them in Propositional Dynamic Logic. While some of our decidability results were known before, we believe that our im ..."
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Cited by 8 (4 self)
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We analyze several classes of path constraints for semistructured data in a uni ed framework and prove some decidability and complexity results for these constraints by embedding them in Propositional Dynamic Logic. While some of our decidability results were known before, we believe that our improved complexity bounds are new. Our proofs, based on techniques from modal logic, shed additional light on the reasons for previously known decidability and complexity results.
Features as Resources in RLFG
 Proceedings of the LFG97 Conference
, 1997
"... This paper describes a new formalization of LexicalFunctional Grammar ..."
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Cited by 8 (1 self)
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This paper describes a new formalization of LexicalFunctional Grammar
Ordering Constraints over Feature Trees Expressed in Secondorder Monadic Logic
 Information and Computation
, 1998
"... The language FT of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. While the firstorder theory of FT is well understood, only few decidability results are known for the firstorder theory of FT . We introduc ..."
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Cited by 8 (4 self)
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The language FT of ordering constraints over feature trees has been introduced as an extension of the system FT of equality constraints over feature trees. While the firstorder theory of FT is well understood, only few decidability results are known for the firstorder theory of FT . We introduce a new method for proving the decidability of fragments of the firstorder theory of FT . This method is based on reduction to second order monadic logic that is decidable according to Rabin's famous tree theorem. The method applies to any fragment of the firstorder theory of FT for which one can change the model towards sufficiently labeled feature trees  a class of trees that we introduce. As we show, the first ordertheory of ordering constraints over sufficiently labeled feature trees is equivalent to secondorder monadic logic (S2S for infinite and WS2S for finite feature trees). We apply our method for proving that entailment of FT with existential quantifiers j 1 j=9x 1 : : :9x n j 2 is decidable. Previous results were restricted to entailment without existential quantifiers which can be solved in cubic time. Meanwhile, entailment with existential quantifiers has been shown PSPACEcomplete (for finite and infinite feature trees respectively).