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89
Conditional XPath
 ACM Trans. Database Syst
, 2005
"... Abstract. XPath 1.0 is a variable free language designed to specify paths between nodes in XML documents. Such paths can alternatively be specified in firstorder logic. The logical abstraction of XPath 1.0, usually called Navigational or Core XPath, is not powerful enough to express every firstord ..."
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Cited by 60 (6 self)
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Abstract. XPath 1.0 is a variable free language designed to specify paths between nodes in XML documents. Such paths can alternatively be specified in firstorder logic. The logical abstraction of XPath 1.0, usually called Navigational or Core XPath, is not powerful enough to express every firstorder definable path. In this paper we show that there exists a natural expansion of Core XPath in which every firstorder definable path in XML document trees is expressible. This expansion is called Conditional XPath. It contains additional axis relations of the form (child::n[F])+, denoting the transitive closure of the path expressed by child::n[F]. The difference with XPath’s descendant::n[F] is that the path (child::n[F])+ is conditional on the fact that all nodes in between should be labeled by n and should make the predicate F true. This result can be viewed as the XPath analogue of the expressive completeness of the relational algebra with respect to firstorder logic. 1
Web and Semantic Web Query Languages: A Survey
"... A number of techniques have been developed to facilitate powerful data retrieval on the Web and Semantic Web. Three categories of Web query languages can be distinguished, according to the format of the data they can retrieve: XML, RDF and Topic Maps. This article introduces the spectrum of langu ..."
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Cited by 47 (21 self)
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A number of techniques have been developed to facilitate powerful data retrieval on the Web and Semantic Web. Three categories of Web query languages can be distinguished, according to the format of the data they can retrieve: XML, RDF and Topic Maps. This article introduces the spectrum of languages falling into these categories and summarises their salient aspects. The languages are introduced using common sample data and query types. Key aspects of the query languages considered are stressed in a conclusion.
Counting in Trees for Free
, 2004
"... In [22], it was shown that MSO logic for ordered unranked trees becomes undecidable if Presburger constraints are allowed at children of nodes. We now show that a decidable logic is obtained if we use a a modal fixpoint logic instead. We present an automata theoretic characterization of this logi ..."
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Cited by 43 (2 self)
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In [22], it was shown that MSO logic for ordered unranked trees becomes undecidable if Presburger constraints are allowed at children of nodes. We now show that a decidable logic is obtained if we use a a modal fixpoint logic instead. We present an automata theoretic characterization of this logic by means of deterministic Presburger tree automata (PTA) and show how it can be used to express numerical document queries. Surprisingly, the complexity of satisfiability for the extended logic is asymptotically the same as for the original logic. The nonemptiness for PTAs is in general pspacecomplete which is moderate given that it is already pspacehard to test whether the complement of a regular expression is nonempty. We also identify a subclass of PTAs with a tractable nonemptiness problem. Further, to decide whether a tree t satisfies a formula # is polynomial in the size of # and linear in the size of t.
Querying unranked trees with stepwise tree automata
 Intenational Conf. on Rewriting Techniques and Applications
, 2004
"... Abstract. The problem of selecting nodes in unranked trees is the most basic querying problem for XML. We propose stepwise tree automata for querying unranked trees. Stepwise tree automata can express the same monadic queries as monadic Datalog and monadic secondorder logic. We prove this result by ..."
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Cited by 42 (20 self)
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Abstract. The problem of selecting nodes in unranked trees is the most basic querying problem for XML. We propose stepwise tree automata for querying unranked trees. Stepwise tree automata can express the same monadic queries as monadic Datalog and monadic secondorder logic. We prove this result by reduction to the ranked case, via a new systematic correspondence that relates unranked and ranked queries. 1
LOGICS FOR UNRANKED TREES: AN OVERVIEW
 CONSIDERED FOR PUBLICATION IN LOGICAL METHODS IN COMPUTER SCIENCE
, 2006
"... Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to ..."
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Cited by 37 (6 self)
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Labeled unranked trees are used as a model of XML documents, and logical languages for them have been studied actively over the past several years. Such logics have different purposes: some are better suited for extracting data, some for expressing navigational properties, and some make it easy to relate complex properties of trees to the existence of tree automata for those properties. Furthermore, logics differ significantly in their modelchecking properties, their automata models, and their behavior on ordered and unordered trees. In this paper we present a survey of logics for unranked trees.
PDL for ordered trees
 JOURNAL OF APPLIED NONCLASSICAL LOGICS
, 2005
"... This paper is about a special version of PDL, proposed by Marcus Kracht, for reasoning about sibling ordered trees. It has four basic programs corresponding to the child, parent, left and rightsibling relations in such trees. The original motivation for this language is rooted in the field of mod ..."
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Cited by 28 (0 self)
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This paper is about a special version of PDL, proposed by Marcus Kracht, for reasoning about sibling ordered trees. It has four basic programs corresponding to the child, parent, left and rightsibling relations in such trees. The original motivation for this language is rooted in the field of modeltheoretic syntax. Motivated by recent developments in the area of semistructured data, and, especially, in the field of query languages for XML (eXtensible Markup Language) documents, we revisit the language. This renewed interest comes with a special focus on complexity and expressivity aspects of the language, aspects that have so far largely been ignored. We survey and derive complexity results, and spend most of the paper on the most important open question concerning the language: what is its expressive power? We approach this question from two angles: Which firstorder properties can be expressed? And which secondorder properties? While we are still some way from definitive answers to these questions, we discuss two firstorder fragments of the PDL language for ordered trees, and show how the language can be used to express some typical (secondorder) problems, like the boolean circuit and the frontier problem.
Firstorder and temporal logics for nested words
 In LICS 2007
"... Nested words are a structured model of execution paths in procedural programs, reflecting their call and return nesting structure. Finite nested words also capture the structure of parse trees and other treestructured data, such as XML. We provide new temporal logics for finite and infinite nested ..."
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Cited by 27 (4 self)
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Nested words are a structured model of execution paths in procedural programs, reflecting their call and return nesting structure. Finite nested words also capture the structure of parse trees and other treestructured data, such as XML. We provide new temporal logics for finite and infinite nested words, which are natural extensions of LTL, and prove that these logics are firstorder expressivelycomplete. One of them is based on adding a ”within” modality, evaluating a formula on a subword, to a logic CaRet previously studied in the context of verifying properties of recursive state machines. The other logic is based on the notion of a summary path that combines the linear and nesting structures. For that logic, both modelchecking and satisfiability are shown to be EXPTIMEcomplete. Finally, we prove that firstorder logic over nested words has the threevariable property, and we present a temporal logic for nested words which is complete for the twovariable fragment of firstorder. 1
The Personal Publication Reader: Illustrating Web Data Extraction, Personalization and Reasoning for the Semantic Web
 In European Semantic Web Conference ESWC 2005, Heraklion, Greece, May 29
, 2005
"... This paper shows how Semantic Web technologies enable the design and implementation of advanced, personalized information systems. We demonstrate by means of an example application how personalized content syndication can be realized in the Semantic Web. Our approach consists of two main parts: ..."
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Cited by 27 (16 self)
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This paper shows how Semantic Web technologies enable the design and implementation of advanced, personalized information systems. We demonstrate by means of an example application how personalized content syndication can be realized in the Semantic Web. Our approach consists of two main parts: The web data extraction part, providing the information system with realtime, dynamic data, and the personalization part, which deduces  with the aid of ontological domain knowledge  personalized views on the data. The prototype of the system has been realized using the Personal Reader Framework for designing, implementing, and maintaining Web content Readers .
Reasoning about XML with Temporal Logics and Automata
 In LPAR’08
"... We show that problems arising in static analysis of XML specifications and transformations can be dealt with using techniques similar to those developed for static analysis of programs. Many properties of interest in the XML context are related to navigation, and can be formulated in temporal logics ..."
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Cited by 25 (4 self)
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We show that problems arising in static analysis of XML specifications and transformations can be dealt with using techniques similar to those developed for static analysis of programs. Many properties of interest in the XML context are related to navigation, and can be formulated in temporal logics for trees. We choose a logic that admits a simple singleexponential translation into unranked tree automata, in the spirit of the classical LTLtoBüchi automata translation. Automata arising from this translation have a number of additional properties; in particular, they are convenient for reasoning about unary nodeselecting queries, which are important in the XML context. We give two applications of such reasoning: one deals with a classical XML problem of reasoning about navigation in the presence of schemas, and the other relates to verifying security properties of XML views.