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182
Caterpillars: A Context Specification Technique
 Markup Languages
, 2000
"... We present a novel, yet simple, technique for the specification of context in structured documents that we call caterpillar expressions. Although we are primarily applying this technique in the specification of contextdependent style sheets for HTML, SGML and XML documents, it can also be used f ..."
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Cited by 34 (7 self)
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We present a novel, yet simple, technique for the specification of context in structured documents that we call caterpillar expressions. Although we are primarily applying this technique in the specification of contextdependent style sheets for HTML, SGML and XML documents, it can also be used for query specification for structured documents, as we shall demonstrate, and for the specification of computer program transformations. From a conceptual point of view, structured documents are trees, and one of the oldest and bestestablished techniques to process trees and, hence, structured documents are tree automata. We present a number of theoretical results that allow us to compare the expressive power of caterpillar expressions and caterpillar automata, their companions, to the expressive power of tree automata. In particular, we demonstrate that each caterpillar expression describes a regular tree language that is, hence, recognizable by a tree automaton. Finally, we empl...
Finite Representation of Infinite Query Answers
, 1992
"... : We define here a formal notion of finite representation of infinite query answers in logic programs. We apply this notion to Datalog nS (Datalog with n successors): an extension of Datalog capable of representing infinite phenomena like flow of time or plan construction. Predicates in Datalog nS ..."
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Cited by 29 (5 self)
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: We define here a formal notion of finite representation of infinite query answers in logic programs. We apply this notion to Datalog nS (Datalog with n successors): an extension of Datalog capable of representing infinite phenomena like flow of time or plan construction. Predicates in Datalog nS can have arbitrary unary and limited nary function symbols in one fixed position. This class of logic programs is known to be decidable. However, least Herbrand models of Datalog nS programs may be infinite and consequently queries may have infinite answers. We present a method to finitely represent infinite least Herbrand models of Datalog nS programs as relational specifications. A relational specification consists of a finite set of facts and a finitely specified congruence relation. A relational specification has the following desirable properties. First, it is explicit in the sense that once it is computed, the original Datalog nS program (and its underlying computational engine) can ...
Interconvertibility of Set Constraints and ContextFree Language Reachability
 In Proceedings of the ACM SIGPLAN Symposium on Partial Evaluation and SemanticsBased Program Manipulation
, 1996
"... We show the interconvertibility of contextfreelanguage reachability problems and a class of setconstraint problems: given a contextfreelanguage reachability problem, we show how to construct a setconstraint problem whose answer gives a solution to the reachability problem; given a setconstrai ..."
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Cited by 29 (1 self)
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We show the interconvertibility of contextfreelanguage reachability problems and a class of setconstraint problems: given a contextfreelanguage reachability problem, we show how to construct a setconstraint problem whose answer gives a solution to the reachability problem; given a setconstraint problem, we show how to construct a contextfreelanguage reachability problem whose answer gives a solution to the setconstraint problem. The interconvertibility of these two formalisms offers an conceptual advantage akin to the advantage gained from the interconvertibility of finitestate automata and regular expressions in formal language theory, namely, a problem can be formulated in whichever formalism is most natural. It also offers some insight into the "O(n³) bottleneck" for different types of programanalysis problems, and allows results previously obtained for contextfreelanguage reachability problems to be applied to setconstraint problems.
Interconvertibility of a Class of Set Constraints and ContextFreeLanguage Reachability
 TCS
, 1998
"... We show the interconvertibility of contextfreelanguage reachability problems and a class of setconstraint problems: given a contextfreelanguage reachability problem, we show how to construct a setconstraint problem whose answer gives a solution to the reachability problem; given a setconstra ..."
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Cited by 27 (2 self)
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We show the interconvertibility of contextfreelanguage reachability problems and a class of setconstraint problems: given a contextfreelanguage reachability problem, we show how to construct a setconstraint problem whose answer gives a solution to the reachability problem; given a setconstraint problem, we show how to construct a contextfreelanguage reachability problem whose answer gives a solution to the setconstraint problem. The interconvertibility of these two formalisms offers an conceptual advantage akin to the advantage gained from the interconvertibility of finitestate automata and regular expressions in formal language theory, namely, a problem can be formulated in whichever formalism is most natural. It also offers some insight into the "O(n ) bottleneck" for different types of programanalysis problems and allows results previously obtained for contextfreelanguage reachability problems to be applied to setconstraint problems and vice versa.
Capturing Practical Natural Language Transformations
"... We study automata for capturing transformations employed by practical natural language processing systems, such as those that translate between human languages. For several variations of finitestate string and tree transducers, we ask formal questions about expressiveness, modularity, teachability, ..."
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Cited by 27 (0 self)
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We study automata for capturing transformations employed by practical natural language processing systems, such as those that translate between human languages. For several variations of finitestate string and tree transducers, we ask formal questions about expressiveness, modularity, teachability, and generalization.
Regular Tree Languages Over NonRanked Alphabets
, 1998
"... F64.24> ffl denotes the empty string. Definition 1.1 We define the set of nodes nodes(t) of a tree t as a set of strings of natural numbers. The definition is by induction on t. 1. For a tree a() with just one node labelled a we define nodes(a()) = ffflg: 2. For a tree a(t 1 ; : : : ; t n ), n ..."
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Cited by 26 (0 self)
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F64.24> ffl denotes the empty string. Definition 1.1 We define the set of nodes nodes(t) of a tree t as a set of strings of natural numbers. The definition is by induction on t. 1. For a tree a() with just one node labelled a we define nodes(a()) = ffflg: 2. For a tree a(t 1 ; : : : ; t n ), n 1, we define nodes(a(t 1 ; : : : ; t n ) = [ 1in i \Delta nodes(t i ) [ ffflg: The nodes of a tree viewed as a term correspond to occurrences of subterms. We denote nodes of trees with .
Deterministic Automata on Unranked Trees
 In Proceedings of the 15th International Symposium on Fundamentals of Computation Theory (FCT), LNCS
, 2005
"... We investigate bottomup and topdown deterministic automata on unranked trees. We show that for an appropriate definition of bottomup deterministic automata it is possible to minimize the number of states e#ciently and to obtain a unique canonical representative of the accepted tree language. ..."
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Cited by 25 (1 self)
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We investigate bottomup and topdown deterministic automata on unranked trees. We show that for an appropriate definition of bottomup deterministic automata it is possible to minimize the number of states e#ciently and to obtain a unique canonical representative of the accepted tree language. For topdown deterministic automata it is well known that they are less expressive than the nondeterministic ones.
Dead Code Elimination through Dependent Types
 In The First International Workshop on Practical Aspects of Declarative Languages
, 1999
"... . Pattern matching is an important feature in various functional programming languages such as SML, Caml, Haskell, etc. In these languages, unreachable or redundant matching clauses, which can be regarded as a special form of dead code, are a rich source for program errors. Therefore, eliminating un ..."
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Cited by 25 (11 self)
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. Pattern matching is an important feature in various functional programming languages such as SML, Caml, Haskell, etc. In these languages, unreachable or redundant matching clauses, which can be regarded as a special form of dead code, are a rich source for program errors. Therefore, eliminating unreachable matching clauses at compiletime can significantly enhance program error detection. Furthermore, this can also lead to significantly more efficient code at runtime. We present a novel approach to eliminating unreachable matching clauses through the use of the dependent type system of DML, a functional programming language that enriches ML with a restricted form of dependent types. We then prove the correctness of the approach, which consists of the major technical contribution of the paper. In addition, we demonstrate the applicability of our approach to dead code elimination through some realistic examples. This constitutes a practical application of dependent types to functional ...
Logics For ContextFree Languages
, 1995
"... We define matchings, and show that they capture the essence of contextfreeness. More precisely, we show that the class of contextfree languages coincides with the class of those sets of strings which can be defined by sentences of the form 9 b', where ' is first order, b is a binary predicate sym ..."
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Cited by 23 (5 self)
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We define matchings, and show that they capture the essence of contextfreeness. More precisely, we show that the class of contextfree languages coincides with the class of those sets of strings which can be defined by sentences of the form 9 b', where ' is first order, b is a binary predicate symbol, and the range of the second order quantifier is restricted to the class of matchings. Several variations and extensions are discussed.