1,445 research outputs found
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
Logics for Unranked Trees: An Overview
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 model-checking
properties, their automata models, and their behavior on ordered and unordered
trees. In this paper we present a survey of logics for unranked trees
Ensuring Query Compatibility with Evolving XML Schemas
During the life cycle of an XML application, both schemas and queries may
change from one version to another. Schema evolutions may affect query results
and potentially the validity of produced data. Nowadays, a challenge is to
assess and accommodate the impact of theses changes in rapidly evolving XML
applications.
This article proposes a logical framework and tool for verifying
forward/backward compatibility issues involving schemas and queries. First, it
allows analyzing relations between schemas. Second, it allows XML designers to
identify queries that must be reformulated in order to produce the expected
results across successive schema versions. Third, it allows examining more
precisely the impact of schema changes over queries, therefore facilitating
their reformulation
Bisimulations on data graphs
Bisimulation provides structural conditions to characterize indistinguishability from an external observer between nodes on labeled graphs. It is a fundamental notion used in many areas, such as verification, graph-structured databases, and constraint satisfaction. However, several current applications use graphs where nodes also contain data (the so called ādata graphsā), and where observers can test for equality or inequality of data values (e.g., asking the attribute ānameā of a node to be different from that of all its neighbors). The present work constitutes a first investigation of ādata awareā bisimulations on data graphs. We study the problem of computing such bisimulations, based on the observational indistinguishability for XPath āa language that extends modal logics like PDL with tests for data equalityā with and without transitive closure operators. We show that in general the problem is PSPACE-complete, but identify several restrictions that yield better complexity bounds (CO- NP, PTIME) by controlling suitable parameters of the problem, namely the amount of non-locality allowed, and the class of models considered (graphs, DAGs, trees). In particular, this analysis yields a hierarchy of tractable fragments.Fil: Abriola, Sergio Alejandro. Consejo Nacional de Investigaciones CientĆficas y TĆ©cnicas. Oficina de CoordinaciĆ³n Administrativa Ciudad Universitaria. Instituto de InvestigaciĆ³n En Ciencias de la ComputaciĆ³n. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de InvestigaciĆ³n En Ciencias de la Computacion; ArgentinaFil: BarcelĆ³, Pablo. Universidad de Chile; ChileFil: Figueira, Diego. Centre National de la Recherche Scientifique; FranciaFil: Figueira, Santiago. Consejo Nacional de Investigaciones CientĆficas y TĆ©cnicas. Oficina de CoordinaciĆ³n Administrativa Ciudad Universitaria. Instituto de InvestigaciĆ³n En Ciencias de la ComputaciĆ³n. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de InvestigaciĆ³n En Ciencias de la Computacion; Argentin
Reasoning & Querying ā State of the Art
Various query languages for Web and Semantic Web data, both for practical use and as an area of research in the scientific community, have emerged in recent years. At the same time, the broad adoption of the internet where keyword search is used in many applications, e.g. search engines, has familiarized casual users with using keyword queries to retrieve information on the internet. Unlike this easy-to-use querying, traditional query languages require knowledge of the language itself as well as of the data to be queried. Keyword-based query languages for XML and RDF bridge the gap between the two, aiming at enabling simple querying of semi-structured data, which is relevant e.g. in the context of the emerging Semantic Web. This article presents an overview of the field of keyword querying for XML and RDF
Alternating register automata on finite words and trees
We study alternating register automata on data words and data trees in
relation to logics. A data word (resp. data tree) is a word (resp. tree) whose
every position carries a label from a finite alphabet and a data value from an
infinite domain. We investigate one-way automata with alternating control over
data words or trees, with one register for storing data and comparing them for
equality. This is a continuation of the study started by Demri, Lazic and
Jurdzinski. From the standpoint of register automata models, this work aims at
two objectives: (1) simplifying the existent decidability proofs for the
emptiness problem for alternating register automata; and (2) exhibiting
decidable extensions for these models. From the logical perspective, we show
that (a) in the case of data words, satisfiability of LTL with one register and
quantification over data values is decidable; and (b) the satisfiability
problem for the so-called forward fragment of XPath on XML documents is
decidable, even in the presence of DTDs and even of key constraints. The
decidability is obtained through a reduction to the automata model introduced.
This fragment contains the child, descendant, next-sibling and
following-sibling axes, as well as data equality and inequality tests
Bottom-up automata on data trees and vertical XPath
A data tree is a finite tree whose every node carries a label from a finite
alphabet and a datum from some infinite domain. We introduce a new model of
automata over unranked data trees with a decidable emptiness problem. It is
essentially a bottom-up alternating automaton with one register that can store
one data value and can be used to perform equality tests with the data values
occurring within the subtree of the current node. We show that it captures the
expressive power of the vertical fragment of XPath - containing the child,
descendant, parent and ancestor axes - obtaining thus a decision procedure for
its satisfiability problem
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 operators:
intersection; set difference; projection; coprojection; converse; 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 some nontrivial separations and a few surprising collapses.Comment: An extended abstract announcing the results of this paper was
presented at the 14th International Conference on Database Theory, Uppsala,
Sweden, March 201
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
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