Axiomatizations for downward XPath on Data Trees

We give sound and complete axiomatizations for XPath with data tests by "equality" or "inequality", and containing the single "child" axis. This data-aware logic predicts over data trees, which are tree-like structures whose every node contains a label from a finite alphabet and a data value from an infinite domain. The language allows us to compare data values of two nodes but cannot access the data values themselves (i.e. there is no comparison by constants). Our axioms are in the style of equational logic, extending the axiomatization of data-oblivious XPath, by B. ten Cate, T. Litak and M. Marx. We axiomatize the full logic with tests by "equality" and "inequality", and also a simpler fragment with "equality" tests only. Our axiomatizations apply both to node expressions and path expressions. The proof of completeness relies on a novel normal form theorem for XPath with data tests

Model theory, proof theory, and computational aspects of logics for reasoning on data trees

XPath es el lenguaje de consultas más ampliamente utilizado para documentos XML; es un estándar abierto y constituye una World Wide Web Consortium (W3C) Recommendation. Trabajamos con un fragmento de este lenguaje, apropiadamente reinterpretado como una lógica: XPath=, una lógica que puede ser vista como una extensión de la lógica modal básica, pero en el contexto de árboles con datos y, fundamentalmente, con la capacidad de realizar comparación de datos entre nodos. Desarrollamos la teoría de modelos de XPath=(↓), que solo puede navegar el árbol descendiendo, y XPath=(↑↓), que también puede navegar hacia arriba. Obtenemos resultados de definibilidad y separación para los dos tipos de fórmulas en XPath=: expresiones de nodo y expresiones de camino. También desarrollamos la noción de bisimulación binaria para ambos fragmentos, y demostramos un teorema de caracterización al estilo van Benthem para expresiones de camino de XPath=(↓). Encontramos axiomatizaciones ecuacionales correctas y completas para XPath=(↓) y para su fragmento libre de desigualdades de datos XPath=(↓)^-. Para demostrar completitud construimos, para cada expresión de nodo consistente, un árbol finito con datos en cuya raíz se satisface la formula. Extendemos XPath= al universo de grafos con datos, y analizamos la complejidad computacional de decidir si dos nodos en dos grafos con datos son bisimilares. Calculamos cotas ajustadas de complejidad para varios problemas de bisimilaridad y para diferentes universos de modelos. Introducimos LRV, una lógica para navegar sobre árboles con datos múltiples, y obtenemos procedimientos de decisión para el problema de satisfabilidad de LRV y algunos fragmentos al reducirlo al problema de control-state-reachability de diferentes sistemas con contadores.XPath is the most widely used query language for XML documents; it is an open standard and constitutes a World Wide Web Consortium (W3C) Recommendation. We work with a fragment of this language, suitably reinterpreted as a logic: XPath=, which can be seen as an extension of basic modal logic, but in the context of data trees and, fundamentally, with the capacity to deal with data comparisons between nodes. We develop the model theory of both XPath=(↓), which can only navigate the tree downwards, and XPath=(↑↓), which can also navigate upwards. We obtain definability and separation results for the two types of formulas in XPath=: node expressions and path expressions. We also develop the notion of binary bisimulation for both fragments, and prove a van Benthem-style characterization theorem for paths expressions of XPath=(↓). Sound and complete equational axiomatizations are found for XPath=(↓) and for its data-inequality-free fragment XPath=(↓)^-. To prove completeness we construct, for every consistent node expression, a finite data tree where it is satisfied at the root. XPath= is extended to the universe of data graphs, and we analyze the computational complexity of deciding if two pointed data graphs are bisimilar. We calculate tight complexity bounds for various bisimilarity problems and different universes of models We introduce LRV, a logic to navigate over multidata trees, and obtain decision procedures for the satisfiability problem of LRV and some fragments by reducing it to the control-state reachability problem of different counter systems.Fil: Abriola, Sergio Alejandro. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Axiomatizing hybrid xpath with data

In this paper we introduce sound and strongly complete axiomatizations for XPath with data constraints extended with hybrid operators. First, we present HXPath=, a multi-modal version of XPath with data, extended with nominals and the hybrid operator @. Then, we introduce an axiomatic system for HXPath=, and we prove it is strongly complete with respect to the class of abstract data models, i.e., data models in which data values are abstracted as equivalence relations. We prove a general completeness result similar to the one presented in, e.g., [BtC06], that ensures that certain extensions of the axiomatic system we introduce are also complete. The axiomatic systems that can be obtained in this way cover a large family of hybrid XPath languages over different classes of frames, for which we present concrete examples. In addition, we investigate axiomatizations over the class of tree models, structures widely used in practice. We show that a strongly complete, finitary, first-order axiomatization of hybrid XPath over trees does not exist, and we propose two alternatives to deal with this issue. We finally introduce filtrations to investigate the status of decidability of the satisfiability problem for these languages.Fil: Areces, Carlos Eduardo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física. Sección Ciencias de la Computación; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Fervari, Raul Alberto. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física. Sección Ciencias de la Computación; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentin

Axiomatizing Hybrid XPath with Data

In this paper we introduce sound and strongly complete axiomatizations for XPath with data constraints extended with hybrid operators. First, we present HXPath=, a multi-modal version of XPath with data, extended with nominals and the hybrid operator @. Then, we introduce an axiomatic system for HXPath=, and we prove it is strongly complete with respect to the class of abstract data models, i.e., data models in which data values are abstracted as equivalence relations. We prove a general completeness result similar to the one presented in, e.g., [BtC06], that ensures that certain extensions of the axiomatic system we introduce are also complete. The axiomatic systems that can be obtained in this way cover a large family of hybrid XPath languages over different classes of frames, for which we present concrete examples. In addition, we investigate axiomatizations over the class of tree models, structures widely used in practice. We show that a strongly complete, finitary, first-order axiomatization of hybrid XPath over trees does not exist, and we propose two alternatives to deal with this issue. We finally introduce filtrations to investigate the status of decidability of the satisfiability problem for these languages

Structural characterizations of the navigational expressiveness of relation algebras on a tree

Given a document D in the form of an unordered node-labeled tree, we study the expressiveness on D of various basic fragments of XPath, the core navigational language on XML documents. Working from the perspective of these languages as fragments of Tarski's relation algebra, we give characterizations, in terms of the structure of D, for when a binary relation on its nodes is definable by an expression in these algebras. Since each pair of nodes in such a relation represents a unique path in D, our results therefore capture the sets of paths in D definable in each of the fragments. We refer to this perspective on language semantics as the "global view." In contrast with this global view, there is also a "local view" where one is interested in the nodes to which one can navigate starting from a particular node in the document. In this view, we characterize when a set of nodes in D can be defined as the result of applying an expression to a given node of D. All these definability results, both in the global and the local view, are obtained by using a robust two-step methodology, which consists of first characterizing when two nodes cannot be distinguished by an expression in the respective fragments of XPath, and then bootstrapping these characterizations to the desired results.Comment: 58 Page

A Sequent Calculus for a Modal Logic on Finite Data Trees

We investigate the proof theory of a modal fragment of XPath equipped with data (in)equality tests over finite data trees, i.e., over finite unranked trees where nodes are labelled with both a symbol from a finite alphabet and a single data value from an infinite domain. We present a sound and complete sequent calculus for this logic, which yields the optimal PSPACE complexity bound for its validity problem

Algoritmos de tableaux para Xpath con datos

En este trabajo se presenta un cálculo correcto y completo para XPath con datos y caminos descendentes, enriquecido con nominales y operadores de satisfacción. Llamaremos HXPath = (↓) al lenguaje híbrido que resulta de agregar operadores híbridos a XPath. Primero se mencionan aspectos básicos de las lógicas modales, híbridas y de XPath, para luego dar el cálculo de tableaux para XPath = . Finalmente se demuestra completitud del cálculo.En este trabajo se desarrollaron complementos para el sistema de información geográfica QGIS que permiten el preprocesamiento y análisis de series de tiempo del Índice de Vegetación Normalizado (NDVI), útiles para estudiar y comparar la estructura vegetal de diferentes puntos geográficos de interés, a través del tiempo. Las series fueron extraídas a partir de imágenes obtenidas por el sensor MODIS (Moderate Resolution Imaging Spectroradiometer), por un biólogo especialista.Fil: Seiler, Nahuel Germán. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina

Transitive closure logic, nested tree walking automata, and XPath

International audienceWe study FO(MTC), first-order logic with monadic transitive closure, a logical formalism in between FO and MSO on trees. We characterize the expressive power of FO(MTC) in terms of nested tree-walking automata. Using the latter, we show that FO(MTC) is strictly less expressive than MSO, solving an open problem. We also present a temporal logic on trees that is expressively complete for FO(MTC), in the form of an extension of the XML document navigation language XPath 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) for Boolean, unary and binary queries. We also investigate the complexity of the automata model as well as the XPath dialect. We show that query evaluation be done in polynomial time (combined complexity), but that emptiness (or, satisfiability) is 2ExpTime-complete