82 research outputs found
A Visual Language for Web Querying and Reasoning
As XML is increasingly being used to represent information on the Web, query and reasoning languages for such data are needed. This article argues that in contrast to the navigational approach taken in particular by XPath and XQuery, a positional approach as used in the language Xcerpt is better suited for a straightforward visual representation. The constructs of the pattern- and rule-based query language Xcerpt are introduced and it is shown how the visual representation visXcerpt renders these constructs to form a visual query language for XML
Completing Queries: Rewriting of IncompleteWeb Queries under Schema Constraints
Reactive Web systems, Web services, and Web-based publish/
subscribe systems communicate events as XML messages, and in
many cases require composite event detection: it is not sufficient to react
to single event messages, but events have to be considered in relation to
other events that are received over time.
Emphasizing language design and formal semantics, we describe the
rule-based query language XChangeEQ for detecting composite events.
XChangeEQ is designed to completely cover and integrate the four complementary
querying dimensions: event data, event composition, temporal
relationships, and event accumulation. Semantics are provided as
model and fixpoint theories; while this is an established approach for rule
languages, it has not been applied for event queries before
Identification of Design Principles
This report identifies those design principles for a (possibly new) query and transformation
language for the Web supporting inference that are considered essential. Based upon these
design principles an initial strawman is selected. Scenarios for querying the Semantic Web
illustrate the design principles and their reflection in the initial strawman, i.e., a first draft of
the query language to be designed and implemented by the REWERSE working group I4
A Generic Module System forWeb Rule Languages: Divide and Rule
An essential feature in practically usable programming languages is
the ability to encapsulate functionality in reusable modules. Modules make large
scale projects tractable by humans. For Web and Semantic Web programming,
many rule-based languages, e.g. XSLT, CSS, Xcerpt, SWRL, SPARQL, and RIF
Core, have evolved or are currently evolving. Rules are easy to comprehend
and specify, even for non-technical users, e.g. business managers, hence easing
the contributions to the Web. Unfortunately, those contributions are arguably
doomed to exist in isolation as most rule languages are conceived without modularity,
hence without an easy mechanism for integration and reuse. In this paper
a generic module system applicable to many rule languages is presented. We
demonstrate and apply our generic module system to a Datalog-like rule language,
close in spirit to RIF Core. The language is gently introduced along the
EU-Rent use case. Using the Reuseware Composition Framework, the module
system for a concrete language can be achieved almost for free, if it adheres to
the formal notions introduced in this paper
Effective and Efficient Data Access in the Versatile Web Query Language Xcerpt
Access to Web data has become an integral part of many applications
and services. In the past, such data has usually been accessed
through human-tailoredHTMLinterfaces.Nowadays, rich client interfaces
in desktop applications or, increasingly, in browser-based clients ease data
access and allow more complex client processing based on XML or RDF
data retrieved throughWeb service interfaces. Convenient specifications of
the data processing on the client and flexible, expressive service interfaces
for data access become essential in this context.Web query languages such
as XQuery, XSLT, SPARQL, or Xcerpt have been tailored specifically for
such a setting: declarative and efficient access and processing ofWeb data.
Xcerpt stands apart among these languages by its versatility, i.e., its ability
to access not just oneWeb format but many. In this demonstration, two aspects
of Xcerpt are illustrated in detail: The first part of the demonstration
focuses on Xcerpt’s pattern matching constructs and rules to enable effective
and versatile data access. It uses a concrete practical use case from
bibliography management to illustrate these language features. Xcerpt’s
visual companion language visXcerpt is used to provide an intuitive interface
to both data and queries. The second part of the demonstration shows
recent advancements in Xcerpt’s implementation focusing on experimental
evaluation of recent complexity results and optimization techniques, as
well as scalability over a number of usage scenarios and input sizes
Regular Rooted Graph Grammars
In dieser Arbeit wir ein pragmatischer Ansatz zur Typisierung, statischen Analyse und Optimierung von Web-Anfragespachen, speziell Xcerpt, untersucht. Pragmatisch ist der Ansatz in dem Sinne, dass dem Benutzer keinerlei Einschränkungen aus Entscheidbarkeits- oder Effizienzgründen auf modellierbare Typen gestellt werden. Effizienz und Entscheidbarkeit werden stattdessen, falls nötig, durch Vergröberungen bei der Typprüfung erkauft.
Eine Typsprache zur Typisierung von Graph-strukturierten Daten im Web wird eingeführt. Modellierbare Graphen sind so genannte gewurzelte Graphen, welche aus einem Spannbaum und Querreferenzen aufgebaut sind. Die Typsprache basiert auf
reguläre Baum Grammatiken, welche um typisierte Referenzen erweitert wurde. Neben wie im Web mit XML üblichen geordneten strukturierten Daten, sind auch ungeordnete Daten, wie etwa in Xcerpt oder RDF üblich, modellierbar. Der dazu verwendete Ansatz---ungeordnete Interpretation Regulärer Ausdrücke---ist neu. Eine operationale Semantik für geordnete wie ungeordnete Typen wird auf Basis spezialisierter Baumautomaten und sog. Counting Constraints (welche wiederum auf presburgerarithmetische Ausdrücke) basieren. Es wird ferner statische Typ-Prüfung und -Inferenz von Xcerpt Anfrage- und Konstrukttermen, wie auch Optimierung von Xcerpt Anfragen auf Basis von Typinformation eingeführt.This thesis investigates a pragmatic approach to typing, static analysis and static
optimization of Web query languages, in special the Web query language Xcerpt. The
approach is pragmatic in the sense, that no restriction on the types are made for
decidability or efficiency reasons, instead precision is given up if necessary.
Pragmatics on the dynamic side means to use types not only to ensure validity of objects
operating on, but also influencing query selection based on types.
A typing language for typing of graph structured data on the Web is introduced.
The Graphs in mind are based on spanning trees with references, the typing languages
is based on regular tree grammars with typed reference extensions. Beside ordered data
in the spirit of XML, unordered data (i.e. in the spirit of the Xcerpt data model or
RDF) can be modelled using regular expressions under unordered interpretation – this
approach is new. An operational semantics for ordered and unordered types is given
based on specialized regular tree automata and counting constraints (them again based
on Presburger arithmetic formulae). Static type checking of Xcerpt query and construct
terms is introduced, as well as optimization of Xcerpt query terms based on schema
information
Modular Web Queries — From Rules to Stores
Even with all the progress in Semantic technology, accessing Web
data remains a challenging issue with new Web query languages and approaches
appearing regularly. Yet most of these languages, including W3C approaches
such as XQuery and SPARQL, do little to cope with the explosion of the data
size and schemata diversity and richness on the Web. In this paper we propose
a straightforward step toward the improvement of this situation that is simple to
realize and yet effective: Advanced module systems that make partitioning of (a)
the evaluation and (b) the conceptual design of complex Web queries possible.
They provide the query programmer with a powerful, but easy to use high-level
abstraction for packaging, encapsulating, and reusing conceptually related parts
(in our case, rules) of a Web query. The proposed module system combines ease
of use thanks to a simple core concept, the partitioning of rules and their consequences
in flexible “stores”, with ease of deployment thanks to a reduction
semantics. We focus on extending the rule-based Semantic Web query language
Xcerpt with such a module system though the same approach can be applied to
other (rule-based) languages as well
Optical coherence and spin population dynamics in Yb:YSiO single crystals
Yb-doped YSiO crystals are a promising platform for
optical quantum memories in long-distance quantum communications. The relevance
of this material lies in Yb long optical and spin coherence times,
along with a large hyperfine splitting, enabling long quantum storage over
large bandwidths. Mechanisms affecting the optical decoherence are however not
precisely known, especially since low-temperature measurements have so far
focused on the 2 to 4 K range. In this work, we performed two- and three-pulse
photon echoes and spectral hole burning to determine optical homogeneous
linewidths in two 171 Yb:YSO crystals doped at 2 and 10 ppm. Experiments were
performed in the 40 mK to 18 K temperature range, leading to linewidths between
320 Hz, among the narrowest reported for rare-earth ions, and several MHz. Our
results show that above 6 K the homogeneous linewidth is mainly due to an
elastic two-phonon process which results in a slow broadening with temperature,
the homogeneous linewidth reaching only 25 kHz at 10 K. At lower temperatures,
interactions with Yb nuclear spin-flips, paramagnetic defects or
impurities, and also Yb-Yb interactions for the higher concentrated crystal,
are likely the main limiting factor to the homogeneous linewidth. In
particular, we conclude that the direct effect of spin and optical excited
state lifetime is a minor contribution to optical decoherence in the whole
temperature range studied. Our results indicate possible paths and regimes for
further decreasing the homogeneous linewidths or maintaining narrow lines at
higher Yb concentration.Comment: 11 pages, 7 figure for the manuscrip
STUCK IN A MOMENT: TONIC IMMOBILITY PREDICTS POOR QUALITY OF LIFE IN TREATED PTSD PATIENTS
Background: Posttraumatic stress disorder (PTSD) is a prevalent and disabling multisystem disorder, with significant physical
and psychiatric morbidity and poor quality of life (QOL). Although peritraumatic reactions - tonic immobility and dissociation - are
established predictors of PTSD severity and development, there is a dearth of investigation assessing the impact of peritraumatic
reactions on QOL of PTSD patients. Quality of life has become increasingly important in health care and research as a reliable
outcome measure. It comprises psychological, physical, social and environmental domains, providing important information about
the impact of diseases on patient\u27s life. This study aims to investigate the impact of peritraumatic tonic immobility and peritraumatic
dissociation on QOL of PTSD civilian outpatients.
Subjects and methods: It is a cross-sectional study of 50 victims of urban violence with current PTSD, recruited in a specialized
outpatient clinic. Instruments used were: Structured Clinical Interview IV, Peritraumatic Dissociative Experiences Questionnaire,
Tonic Immobility Scale and WHOQOL-BREF (psychological, physical, social and environmental domains). Linear regression
models were fitted to evaluate the impact of peritraumatic reactions - tonic immobility and dissociation - on WHOQOL-BREF
scores. We controlled for sex as potential confounding.
Results: The severity of peritraumatic tonic immobility negatively impacted on psychological and environment domains of
quality of life. For each additional point on the Tonic Immobility Scale, there was a decreased of 0.8 points on the scores of these
domains of WHOQOL-BREF. Neither the peritraumatic reactions showed effects on physical nor social domains. Possible
limitations of this study include cross-sectional design, relatively small sample size of tertiary center outpatients and recall bias.
Conclusions: Peritraumatic tonic immobility is related to poor quality of life, adding new insights about the relationship between
this immobility reaction and PTSD
Leptogenesis and low-energy phases
In supersymmetric models, the CP asymmetry produced in the decay of the
lightest right-handed neutrino, , can be written as a function
of weak scale parameters. We introduce a way of separating epsilon into
contributions from the various weak-scale phases, and study the contribution of
potentially measurable neutrino phases to leptogenesis. We find that the
Majorana phase phi', which could have observable effects on neutrinoless double
beta decay, is important for epsilon unless there are cancellations among
phases. If the phase delta can be measured at a neutrino factory, then it
contributes significantly to epsilon over much of parameter space.Comment: amplified discussion, minor comments added (33 pages, 3 figures
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