Data Summaries for On-Demand Queries over Linked Data

Typical approaches for querying structured Web Data collect (crawl) and pre-process (index) large amounts of data in a central data repository before allowing for query answering. However, this time-consuming pre-processing phase however leverages the benefits of Linked Data – where structured data is accessible live and up-to-date at distributed Web resources that may change constantly – only to a limited degree, as query results can never be current. An ideal query answering system for Linked Data should return current answers in a reasonable amount of time, even on corpora as large as the Web. Query processors evaluating queries directly on the live sources require knowledge of the contents of data sources. In this paper, we develop and evaluate an approximate index structure summarising graph-structured content of sources adhering to Linked Data principles, provide an algorithm for answering conjunctive queries over Linked Data on the Web exploiting the source summary, and evaluate the system using synthetically generated queries. The experimental results show that our lightweight index structure enables complete and up-to-date query results over Linked Data, while keeping the overhead for querying low and providing a satisfying source ranking at no additional cost

Qualitätsmessung, Evaluation, Forschungsrating

Evaluationen, Rankings, Ratings – seit einigen Jahren nimmt die Zahl der Instrumente und Methoden, mit denen (geistes)wissenschaftliche Qualität „gemessen“ werden soll, exorbitant zu. Für Hochschulen, Forschungsinstitute oder Zeitschriften sind sie mittlerweile fester Bestandteil des Wissenschaftsbetriebs geworden. In kaum einem öffentlichen Bereich werden Leistungsvergleiche derzeit so groß geschrieben wie bei den Hochschulen. Die Reaktionen auf diese Entwicklung reichen von enthusiastischer Befürwortung bis zu radikaler Ablehnung. Die Leistungsvergleiche sind Teil und Ausdruck einer Restrukturierung der deutschen (und europäischen) Universitätslandschaft, die fast alle Bereiche von Forschung und Lehre betrifft. Entsprechend groß ist der Diskussionsbedarf. H-Soz-u-Kult veranstaltete aus diesem Anlass das Diskussionsforum „Qualitätsmessung, Evaluation, Forschungsrating. Risiken und Chancen für die Geschichtswissenschaften?“. Die inhaltliche Spannweite der Beiträge reicht von grund-legenden Reflexionen über das Verhältnis von Wissenschaft und Gesellschaft bis zu konkreten Vorstellungen der Ratinginstrumente des Wissenschaftsrats

Patterns of variation in recruitment and post-recruitment processes of the Mediterranean precious gorgonian coral Corallium rubrum

7 pages, 6 figures, 3 tables.This research seeks to quantify recruitment, early survival and early colony growth in different populations of the precious Mediterranean red coral. Although basic to our understanding of red coral ecology and population dynamics, these early life-history descriptors are still poorly understood. To fill this lack of knowledge, marble settlement tiles were placed at 35 ± 1 m depth within 3 populations of Corallium rubrum dwelling in the coralligenous habitat of different geographic areas of the north-western Mediterranean: Calafuria and Elba Island (Italy), and Medes Islands MPA (Spain), following a multifactorial ANOVA model and sampled photographically for four years (2003–2006). Overall, 517 red coral recruits settled on the tiles during the experiment, 189 of which (126 at Calafuria and 63 at Elba) were still surviving, in 2007, when the tiles were removed. The recruitment density at Medes was only one tenth of that at Calafuria and Elba (0.56 ± 0.21 vs. 6.06 ± 1.75 and 4.66 ± 1.01 recruits dm− 2, mean ± SE). No colony survived after four years at Medes, where the lowest recruitment rate was also found. As the age of each new settled colony was known, it was possible to measure the early growth rates of individual colonies. The growth rates thus obtained were two to three times higher than that measured in older colonies and differed significantly between the geographic areas (the growth of colony basal diameter was 0.68 ± 0.02 and 0.59 ± 0.19 mm/year at Calafuria and Elba), while no significant difference was found between the actual colony growth and that previously measured in the former area. A test for secondary substrate selectivity, carried out in one area, showed that red coral preferentially settles on tubes of Serpulida than on other encrusting organisms. However, since recruitment density at Medes was lower despite the four-fold higher cover of Serpulida found there, other factors, intrinsic to the populations, such as different size–age structures or densities, leading to different larval output, may likely have determined red coral recruitment rates in the studied areas.This research was supported by the common Italy–Spain exchange project: Proyecto Cooperación Csic/Cnr 2004t0040 and Azioni Integrate Italia-Spagna 2008. GS was funded by the PRIN 2007 project 200777BWEP: Mathematical population theory. LB was funded by Marie Curie IEF (CORGARD, Project No. 221072) and SR was funded by Ramón y Cajal contract (RYC-2007-01327). We thank Fischer Italy for economical support and A. Cafazzo for his revision of the English text.Peer reviewe

Measurement of the E2/M1 ratio in the N->delta transition using the reaction p((gamma)over-right-arrow,p)pi(0)

The small electric quadrupole E2 amplitude of the predominantly magnetic dipole M1 p --> Delta(1232) transition has been measured using 270 to 320 MeV tagged linearly polarized photons in the p(, p)pi(o) reaction at the Mainz Microtron MAMI. Differential cross sections and photon asymmetries were determined by measuring the recoil proton in the cylindrically symmetric 4 pi detector DAPHNE. From the proton angular distributions the ratio E2/M1 = -(2.5 +/- 0.2 +/- 0.2)% at the maximum of the Delta(1232) resonance has been derived

Determination of the E2/M1 ratio in the (gamma)N→Delta(1232) transition from a simultaneous measurement of p((gamma)over-right-arrow,p)pi(0) and P((gamma)over-right-arrow, pi(+))n

Tagged linearly polarized photons have been used at the Mainz Microtron (MAMI) for simultaneous measurements of the p(,p)pi(0). and p(,pi(+))n reaction channels to study the gamma N-->Delta(1232) transition. The energy dependence of the magnetic dipole M-1+(3/2) and electric quadrupole E-1+(3/2) amplitudes have been extracted from these data in the photon energy range from 270 to 420 MeV. The E2/M1 ratio for the gamma N-->Delta(1232) transition has been determined to be -(2.5+/-0.1(stat)+/-0.2(sys))% at the resonance position (delta(33)=90 degrees)