874 research outputs found
DBpedia's triple pattern fragments: usage patterns and insights
Queryable Linked Data is published through several interfaces, including SPARQL endpoints and Linked Data documents. In October 2014, the DBpedia Association announced an official Triple Pattern Fragments interface to its popular DBpedia dataset. This interface proposes to improve the availability of live queryable data by dividing query execution between clients and servers. In this paper, we present a usage analysis between November 2014 and July 2015. In 9 months time, the interface had an average availability of 99.99 %, handling 16,776,170 requests, 43.0% of which were served from cache. These numbers provide promising evidence that low-cost Triple Pattern Fragments interfaces provide a viable strategy for live applications on top of public, queryable datasets
The Gremlin Graph Traversal Machine and Language
Gremlin is a graph traversal machine and language designed, developed, and
distributed by the Apache TinkerPop project. Gremlin, as a graph traversal
machine, is composed of three interacting components: a graph , a traversal
, and a set of traversers . The traversers move about the graph
according to the instructions specified in the traversal, where the result of
the computation is the ultimate locations of all halted traversers. A Gremlin
machine can be executed over any supporting graph computing system such as an
OLTP graph database and/or an OLAP graph processor. Gremlin, as a graph
traversal language, is a functional language implemented in the user's native
programming language and is used to define the of a Gremlin machine.
This article provides a mathematical description of Gremlin and details its
automaton and functional properties. These properties enable Gremlin to
naturally support imperative and declarative querying, host language
agnosticism, user-defined domain specific languages, an extensible
compiler/optimizer, single- and multi-machine execution models, hybrid depth-
and breadth-first evaluation, as well as the existence of a Universal Gremlin
Machine and its respective entailments.Comment: To appear in the Proceedings of the 2015 ACM Database Programming
Languages Conferenc
Infrared generation in low-dimensional semiconductor heterostructures via quantum coherence
A new scheme for infrared generation without population inversion between
subbands in quantum-well and quantum-dot lasers is presented and documented by
detailed calculations. The scheme is based on the simultaneous generation at
three frequencies: optical lasing at the two interband transitions which take
place simultaneously, in the same active region, and serve as the coherent
drive for the IR field. This mechanism for frequency down-conversion does not
rely upon any ad hoc assumptions of long-lived coherences in the semiconductor
active medium. And it should work efficiently at room temperature with
injection current pumping. For optimized waveguide and cavity parameters, the
intrinsic efficiency of the down-conversion process can reach the limiting
quantum value corresponding to one infrared photon per one optical photon. Due
to the parametric nature of IR generation, the proposed inversionless scheme is
especially promising for long-wavelength (far- infrared) operation.Comment: 4 pages, 1 Postscript figure, Revtex style. Replacement corrects a
printing error in the authors fiel
Direct N-glycosylation profiling of urine and prostatic fluid glycoproteins and extracellular vesicles
Expressed prostatic secretions (EPS), also called post digital rectal exam urines, are proximal fluids of the prostate that are widely used for diagnostic and prognostic assays for prostate cancer. These fluids contain an abundant number of glycoproteins and extracellular vesicles secreted by the prostate gland, and the ability to detect changes in their N-glycans composition as a reflection of disease state represents potential new biomarker candidates. Methods to characterize these N-glycan constituents directly from clinical samples in a timely manner and with minimal sample processing requirements are not currently available. In this report, an approach is described to directly profile the N-glycan constituents of EPS urine samples, prostatic fluids and urine using imaging mass spectrometry for detection. An amine reactive slide is used to immobilize glycoproteins from a few microliters of spotted samples, followed by peptide N-glycosidase digestion. Over 100 N-glycan compositions can be detected with this method, and it works with urine, urine EPS, prostatic fluids, and urine EPS-derived extracellular vesicles. A comparison of the N-glycans detected from the fluids with tissue N-glycans from prostate cancer tissues was done, indicating a subset of N-glycans present in fluids derived from the gland lumens. The developed N-glycan profiling is amenable to analysis of larger clinical cohorts and adaptable to other biofluids
GUN: An Efficient Execution Strategy for Querying the Web of Data
International audienceLocal-As-View (LAV) mediators provide a uniform interface to a federation of heterogeneous data sources, attempting to execute queries against the federation. LAV mediators rely on query rewriters to translate mediator queries into equivalent queries on the federated data sources. The query rewriting problem in LAV mediators has shown to be NP-complete, and there may be an exponential number of rewritings, making unfeasible the execution or even generation of all the rewritings for some queries. The complexity of this problem can be particularly impacted when queries and data sources are described using SPARQL conjunctive queries, for which millions of rewritings could be generated. We aim at providing an efficient solution to the problem of executing LAV SPARQL query rewritings while the gathered answer is as complete as possible. We formulate the Result-Maximal k-Execution problem (ReMakE) as the problem of maximizing the query results obtained from the execution of only k rewritings. Additionally, a novel query execution strategy called GUN is proposed to solve the ReMakE problem. Our experimental evaluation demonstrates that GUN outperforms traditional techniques in terms of answer completeness and execution time
An Optical Time-Delay for the Lensed BAL Quasar HE2149-2745
We present optical V and i-band light curves of the gravitationally lensed
BAL quasar HE2149-2745. The data, obtained with the 1.5m Danish Telescope
(ESO-La Silla) between October 1998 and December 2000, are the first from a
long-term project aimed at monitoring selected lensed quasars in the Southern
Hemisphere. A time delay of 103+/-12 days is determined from the light curves.
In addition, VLT/FORS1 spectra of HE2149-2745 are deconvolved in order to
obtain the spectrum of the faint lensing galaxy, free of any contamination by
the bright nearby two quasar images. By cross-correlating the spectrum with
galaxy-templates we obtain a tentative redshift estimate of z=0.495+/-0.01.
Adopting this redshift, a Omega=0.3, Lambda=0.7 cosmology, and a chosen
analytical lens model, our time-delay measurement yields a Hubble constant of
H_0=66+/-8 km/s/Mpc with an estimated systematic error of +/-3 km/s/Mpc. Using
non-parametric models yields H_0=65+/-8 km/s/Mpc and confirms that the lens
exhibits a very dense/concentrated mass profile.Comment: 11 pages, accepted for publication in Astronomy & Astrophysic
ANAPSID: An Adaptive Query Processing Engine for SPARQL Endpoints
Abstract. Following the design rules of Linked Data, the number of available SPARQL endpoints that support remote query processing is quickly growing; however, because of the lack of adaptivity, query executions may frequently be unsuccessful. First, fixed plans identified following the traditional optimize-then-execute paradigm, may timeout as a consequence of endpoint availability. Sec-ond, because blocking operators are usually implemented, endpoint query en-gines are not able to incrementally produce results, and may become blocked if data sources stop sending data. We present ANAPSID, an adaptive query engine for SPARQL endpoints that adapts query execution schedulers to data availabil-ity and run-time conditions. ANAPSID provides physical SPARQL operators that detect when a source becomes blocked or data traffic is bursty, and opportunis-tically, the operators produce results as quickly as data arrives from the sources. Additionally, ANAPSID operators implement main memory replacement policies to move previously computed matches to secondary memory avoiding duplicates. We compared ANAPSID performance with respect to RDF stores and endpoints, and observed that ANAPSID speeds up execution time, in some cases, in more than one order of magnitude.
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