21 research outputs found
Frontiers of tractability for typechecking simple XML transformations
AbstractTypechecking consists of statically verifying whether the output of an XML transformation is always conform to an output type for documents satisfying a given input type. We focus on complete algorithms which always produce the correct answer. We consider top–down XML transformations incorporating XPath expressions and abstract document types by grammars and tree automata. By restricting schema languages and transformations, we identify several practical settings for which typechecking can be done in polynomial time. Moreover, the resulting framework provides a rather complete picture as we show that most scenarios cannot be enlarged without rendering the typechecking problem intractable. So, the present research sheds light on when to use fast complete algorithms and when to reside to sound but incomplete ones
On the complexity of typechecking top-down XML transformations
AbstractWe investigate the typechecking problem for XML transformations: statically verifying that every answer to a transformation conforms to a given output schema, for inputs satisfying a given input schema. As typechecking quickly turns undecidable for query languages capable of testing equality of data values, we return to the limited framework where we abstract XML documents as labeled ordered trees. We focus on simple top-down recursive transformations motivated by XSLT and structural recursion on trees. We parameterize the problem by several restrictions on the transformations (deleting, non-deleting, bounded width) and consider both tree automata and DTDs as input and output schemas. The complexity of the typechecking problems in this scenario ranges from PTIME to EXPTIME
Rewrite based Verification of XML Updates
We consider problems of access control for update of XML documents. In the
context of XML programming, types can be viewed as hedge automata, and static
type checking amounts to verify that a program always converts valid source
documents into also valid output documents. Given a set of update operations we
are particularly interested by checking safety properties such as preservation
of document types along any sequence of updates. We are also interested by the
related policy consistency problem, that is detecting whether a sequence of
authorized operations can simulate a forbidden one. We reduce these questions
to type checking problems, solved by computing variants of hedge automata
characterizing the set of ancestors and descendants of the initial document
type for the closure of parameterized rewrite rules
Static Analysis of Graph Database Transformations
We investigate graph transformations, defined using Datalog-like rules based
on acyclic conjunctive two-way regular path queries (acyclic C2RPQs), and we
study two fundamental static analysis problems: type checking and equivalence
of transformations in the presence of graph schemas. Additionally, we
investigate the problem of target schema elicitation, which aims to construct a
schema that closely captures all outputs of a transformation over graphs
conforming to the input schema. We show all these problems are in EXPTIME by
reducing them to C2RPQ containment modulo schema; we also provide matching
lower bounds. We use cycle reversing to reduce query containment to the problem
of unrestricted (finite or infinite) satisfiability of C2RPQs modulo a theory
expressed in a description logic
Web and Semantic Web Query Languages
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
Mu-Calculus Based Resolution of XPath Decision Problems
XPath is the standard declarative notation for navigating XML data and returning a set of matching nodes. In the context of XSLT/XQuery analysis, query optimization, and XML type checking, XPath decision problems arise naturally. They notably include XPath containment (whether or not for any tree the result of a particular query is included in the result of a second one), and XPath satisfiability (whether or not an expression yields a non-empty result), in the presence (or the absence) of XML DTDs. In this paper, we propose a unifying logic for XML, namely the alternation-free modal mu-calculus with converse. We show how to translate major XML concepts such as XPath and DTDs into this logic. Based on these embeddings, we show how XPath decision problems can be solved using a state-of-the-art EXPTIME decision procedure for mu-calculus satisfiability. We provide preliminary experiments which shed light, for the first time, on the cost of solving XPath decision problems in practice
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