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21
On the complexity of XPath containment in the presence of disjunction, DTDs, and variables
 Logical Methods in Computer Science
"... Vol. 2 (3:1) 2006, pp. 1–1–30 www.lmcsonline.org ..."
The complexity of query containment in expressive fragments of XPath 2.0
 In Proc. PODS’07
, 2007
"... (full version, including appendices, of the PODS’07 paper) ..."
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Cited by 25 (5 self)
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(full version, including appendices, of the PODS’07 paper)
XPath, transitive closure logic, and nested tree walking automata
 In Proceedings PODS 2008
, 2008
"... We consider the navigational core of XPath, extended with two operators: the Kleene star for taking the transitive closure of path expressions, and a subtree relativisation operator, allowing one to restrict attention to a specific subtree while evaluating a subexpression. We show that the expressiv ..."
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Cited by 19 (0 self)
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We consider the navigational core of XPath, extended with two operators: the Kleene star for taking the transitive closure of path expressions, and a subtree relativisation operator, allowing one to restrict attention to a specific subtree while evaluating a subexpression. We show that the expressive power of this XPath dialect equals that of FO(MTC), first order logic extended with monadic transitive closure. We also give a characterization in terms of nested treewalking automata. Using the latter we then proceed to show that the language is strictly less expressive than MSO. This solves an open question about the relative expressive power of FO(MTC) and MSO on trees. We also investigate the complexity for our XPath dialect. We show that query evaluation be done in polynomial time (combined complexity), but that satisfiability and query containment (as well as emptiness for our automaton model) are 2ExpTimecomplete (it is ExpTimecomplete for Core XPath).
Articulating information needs in XML query languages
 Transactions on Information Systems
"... Documentcentric XML is a mixture of text and structure. With the increased availability of documentcentric XML documents comes a need for query facilities in which both structural constraints and constraints on the content of the documents can be expressed. How does the expressiveness of languages ..."
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Cited by 16 (10 self)
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Documentcentric XML is a mixture of text and structure. With the increased availability of documentcentric XML documents comes a need for query facilities in which both structural constraints and constraints on the content of the documents can be expressed. How does the expressiveness of languages for querying XML documents help users to express their information needs? We address this question from both an experimental and a theoretical point of view. Our experimental analysis compares a structureignorant with a structureaware retrieval approach using the test suite of the INEX XML retrieval evaluation initiative. Theoretically, we create two mathematical models of users ’ knowledge of a set of documents and define query languages which exactly fit these models. One of these languages corresponds to an XML version of fielded search, the other to the INEX query language. Our main experimental findings are: First, while structure is used in varying degrees of complexity, two thirds of the queries can be expressed in a fieldedsearch like format which does not use the hierarchical structure of the documents. Second, three quarters of the queries use constraints on the context of the elements to be returned; these contextual constraints cannot be captured by ordinary keyword queries. Third, structure is used as a search hint, and not as a strict requirement, when judged against the underlying information need. Fourth, the use of structure in queries functions as a precision enhancing device.
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 14 (3 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
Probabilistic XML via Markov Chains
, 2009
"... We show how Recursive Markov Chains (RMCs) and their restrictions can define probabilistic distributions over XML documents, and study tractability ..."
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Cited by 11 (8 self)
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We show how Recursive Markov Chains (RMCs) and their restrictions can define probabilistic distributions over XML documents, and study tractability
Navigational XPath: calculus and algebra
, 2007
"... We survey expressivity results for navigational fragments of XPath 1.0 and 2.0, as well as Regular XPath ≈. We also investigate algebras for these fragments. ..."
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Cited by 7 (2 self)
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We survey expressivity results for navigational fragments of XPath 1.0 and 2.0, as well as Regular XPath ≈. We also investigate algebras for these fragments.
Unary negation
, 2011
"... We study fragments of firstorder logic and of least fixed point logic that allow only unary negation: negation of formulas with at most one free variable. These logics generalize many interesting known formalisms, including modal logic and the µcalculus, as well as conjunctive queries and monadic ..."
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Cited by 4 (2 self)
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We study fragments of firstorder logic and of least fixed point logic that allow only unary negation: negation of formulas with at most one free variable. These logics generalize many interesting known formalisms, including modal logic and the µcalculus, as well as conjunctive queries and monadic Datalog. We show that satisfiability and finite satisfiability are decidable for both fragments, and we pinpoint the complexity of satisfiability, finite satisfiability, and model checking. We also show that the unary negation fragment of firstorder logic is modeltheoretically very well behaved. In particular, it enjoys Craig interpolation and the Beth property.
Relative Expressive Power of Navigational Querying on Graphs
"... Motivated by both established and new applications, we study navigational query languages for graphs (binary relations). The simplest language has only the two operators union and composition, together with the identity relation. We make more powerful languages by adding any of the following operato ..."
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Cited by 4 (0 self)
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Motivated by both established and new applications, we study navigational query languages for graphs (binary relations). The simplest language has only the two operators union and composition, together with the identity relation. We make more powerful languages by adding any of the following operators: intersection; set difference; projection; coprojection; converse; transitive closure; and the diversity relation. All these operators map binary relations to binary relations. We compare the expressive power of all resulting languages. We do this not only for general path queries (queries where the result may be any binary relation) but also for boolean or yes/no queries (expressed by the nonemptiness of an expression). For both cases, we present the complete Hasse diagram of relative expressiveness. In particular, the Hasse diagram for boolean queries contains nontrivial separations and a few surprising collapses.
Logical foundations of XML and XQuery
"... XML is the underlying representation formalism of much webdata. Thus to reason about webdata essentially boils down to reasoning about data in XML format. In this course the students learn about the main languages for querying XML data: XPath and XQuery. The course contains both theoretical work ..."
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Cited by 3 (0 self)
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XML is the underlying representation formalism of much webdata. Thus to reason about webdata essentially boils down to reasoning about data in XML format. In this course the students learn about the main languages for querying XML data: XPath and XQuery. The course contains both theoretical work and practical examples.