Quantifizierung des zu erwartenden Nutzens von Datenbankreorganisationen     

Stefan Dorendorf 《Informatik - Forschung und Entwicklung》2005,20(1-2):72-89

Stetig wachsende Datenmengen und hohe Verfügbarkeitsanforderungen an Datenbanken führen dazu, dass Wartungsarbeiten (wie z.B. Datenbankreorganisationen) oft nicht mehr (oder nicht mehr vollst?ndig) offline in zur Verfügung stehenden Zeitfenstern durchgeführt werden k?nnen bzw. dass die Kosten oder die Behinderungen des normalen Datenbankbetriebs bei online durchgeführten Wartungsarbeiten nicht mehr vernachl?ssigt werden k?nnen. Deshalb sollte vorab bestimmt (quantifiziert) werden, ob der zu erwartende Nutzen den mit der Reorganisation verbundenen Aufwand rechtfertigt. Es ist daher wichtig, die Datenbankobjekte zu lokalisieren und einzugrenzen, bei denen ein hoher Wartungsbedarf besteht. Weiterhin ist es wünschenswert, zun?chst den durch Wartungsma?nahmen erreichbaren Nutzen vor ihrer Durchführung quantifizieren zu k?nnen. Dieser Nutzen ist auch von der Workload abh?ngig, also von den gegen die Datenbankobjekte gerichteten Datenbankanweisungen und deren Ausführungsh?ufigkeiten. Insbesondere der zur Workload-Abarbeitung anfallende I/O-Aufwand, der einen dominierenden Anteil am Gesamtaufwand ausmacht, l?sst sich mit einer Datenbankreorganisation u.U. wesentlich beeinflussen (reduzieren). In diesem Beitrag wird eine Methode vorgestellt, die es erm?glicht, die Auswirkungen einer Datenbankreorganisation auf den zur Workload-Abarbeitung notwendigen I/O-Aufwand abzusch?tzen und damit den haupts?chlichen Nutzen der Reorganisation zu quantifizieren. über erste Erfahrungen mit der Methode, die anhand von Beispielen gesammelt wurden, wird berichtet. The permanent increasing amount of data and the requirement of high availability cause that maintenance of databases (e.g. database reorganizations) often is not or not completely (off-line) possible in the available time spans. On-line database reorganizations are often expensive and cumbersome during the normal database processing. To reduce performance impacts it is important to locate the database objects that have a high level of disorganization and so a high need of maintenance. Furthermore, it is desirable to be able to estimate the benefit of expensive maintenance operations before their processing. This benefit depends on the degree of disorganization and on the instructions that are processed on the database objects (workload). In particular, the costs for I/O-operations dominate the total costs for database operations. With database reorganizations it is possible to reduce the I/O-costs. In this paper we present a method to calculate the benefit of database reorganizations before the processing. The presented method allows to calculate the possible reduction of the I/O-cost for processing a given workload caused by a database reorganization.

CR Subject Classification E.2,H.2.7,H.3.2,H.3.3  相似文献   

Biomechanical validation of a specific upper body training and testing drill in cross-country skiing   总被引：1，自引：0，他引：1  

Stöggl T  Lindinger S  Müller E 《Sports biomechanics / International Society of Biomechanics in Sports》2006,5(1):23-46

The aim of this study was to perform a biomechanical validation of a double poling imitation drill on a rollerboard. Six elite cross-country skiers performed three imitation drill trials at maximal speed at 13 degrees inclination and in double poling on roller skis on a paved road of 3 degrees. Pole and strap forces, elbow and hip angles and EMG activity of eight upper body muscles were measured. Force curves showed similar characteristics, except for impact force occurring only at pole plant in double poling on roller skis. Double poling on a rollerboard includes an eccentric roll-down phase not appearing in double polling on roller skis. Forces on the rollerboard were similar to those on roller skis. Courses of the elbow angles indicated similar shapes, except for the angle at the start of the propulsion phase and, consequently, during flexion (p < 0.01). Propulsion time and cycle duration were longer and frequency lower on the rollerboard (all p < 0.001). Muscle activities were not significantly different, except for stronger biceps brachii (p < 0.01) and weaker erector spinae activation (p < 0.05) on the rollerboard. Muscle coordination patterns showed similar onset and offset points of each muscle and comparable activations in both activities, except for biceps brachii. Two movement strategies on the rollerboard were found, which led to small differences in measured variables. The biomechanical validity of double poling on a rollerboard can be judged as moderately high, being aware of the differences in some variables that might be considered in training sessions on the rollerboard, particularly when using intervals with high number of repetitions.  相似文献   

Biomechanical comparison of the double-push technique and the conventional skate skiing technique in cross-country sprint skiing   总被引：1，自引：0，他引：1  

Stöggl T  Müller E  Lindinger S 《Journal of sports sciences》2008,26(11):1225-1233

The aims of the study were to: (1) adapt the "double-push" technique from inline skating to cross-country skiing; (2) compare this new skiing technique with the conventional skate skiing cross-country technique; and (3) test the hypothesis that the double-push technique improves skiing speed in a short sprint. 13 elite skiers performed maximum-speed sprints over 100 m using the double-push skate skiing technique and using the conventional "V2" skate skiing technique. Pole and plantar forces, knee angle, cycle characteristics, and electromyography of nine lower body muscles were analysed. We found that the double-push technique could be successfully transferred to cross-country skiing, and that this new technique is faster than the conventional skate skiing technique. The double-push technique was 2.9 +/- 2.2% faster (P < 0.001), which corresponds to a time advantage of 0.41 +/- 0.31 s over 100 m. The double-push technique had a longer cycle length and a lower cycle rate, and it was characterized by higher muscle activity, higher knee extension amplitudes and velocities, and higher peak foot forces, especially in the first phase of the push-off. Also, the foot was more loaded laterally in the double-push technique than in the conventional skate skiing technique.  相似文献   

Der Einfluss des Alters auf Spielerfolg und Spielverlauf im Seniorengolf der Weltklasse     

Manfred  Stefan Letzelter 《Sportwissenschaft》2008,38(3):288-302

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Die Messung aktuellen Wohlbefindens im Gesundheitssport     

Dr. Heiko Ziemainz  Stefan Peters 《Sportwissenschaft》2010,40(3):174-181

There is a growing body of evidence that physical activity has under certain circumstances a positive influence on actual well-being. Actors in health sports should hence be able to investigate their actions regarding the influence on the well-being of the participants. The purpose of this review is to give an overview of the existing methods of measurement concerning actual well-being and to publish recommendations for the practical application. Therefore the search was narrowed down to multidimensional questionnaires, measuring the actual well-being. Five instruments, e. g. Positive and Negative Affect Schedule (PANAS), “Befindlichkeitsskalen” (BFS), Profile of Mood States (POMS) are finally reviewed after an introduction which outlines the categories of well-being and reviews the mechanisms which have been suggested to explain the beneficial effects of exercise. The questionnaires vary sizably concerning the theoretical background, the psychometric properties and their structure. The suitability for various domains can be verified regarding these differences. The POMS for example can be recommended because of the international comparability, the PANAS because of the time-efficient use and the BFS because of their extensive use in the German-speaking world.  相似文献   

Postmodernism: a 'Sceptical' Challenge in Educational Theory     

Stefan Ramaekers 《Journal of Philosophy of Education》2002,36(4):629-651

Recently several educational theorists have argued for the incorporation of a scepticism of a postmodern kind into educational theory and into educational research more specifically. Their understanding of postmodernism in terms of scepticism harbours much potential, but to avoid confusion and misunderstanding it is of importance that the 'scepticism' associated with postmodernism is distinguished from traditional philosophical scepticism, be it as part of the very process of theoretical scrutiny or as a challenge towards its results. In this paper it will be argued that the interest of postmodernist 'scepticism' lies not in a quest for ever more certainty but rather in the way it moves beyond both foundationalism and philosophical scepticism. This will be elaborated from the point of view of a Wittgensteinian understanding of theoretical scrutiny (as found in On Certainty). This opens up the possibility of shedding light on postmodernist 'scepticism' in educational theory in terms of an aesthetic distance towards what is reflected upon.  相似文献   

Sportspiel-Forschung — zwischen Trainerbank und Lehrstuhl     

Stefan König 《Sportwissenschaft》1997,27(3):350-353

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Editorial     

Theo H?rder  Stefan J?hnichen 《Informatik - Forschung und Entwicklung》2004,2(1):103-104

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Enhancing the MeSH thesaurus to retrieve French online health resources in a quality-controlled gateway     

Douyère M  Soualmia LF  Névéol A  Rogozan A  Dahamna B  Leroy JP  Thirion B  Darmoni SJ 《Health information and libraries journal》2004,21(4):253-261

The amount of health information available on the Internet is considerable. In this context, several health gateways have been developed. Among them, CISMeF (Catalogue and Index of Health Resources in French) was designed to catalogue and index health resources in French. The goal of this article is to describe the various enhancements to the MeSH thesaurus developed by the CISMeF team to adapt this terminology to the broader field of health Internet resources instead of scientific articles for the medline bibliographic database. CISMeF uses two standard tools for organizing information: the MeSH thesaurus and several metadata element sets, in particular the Dublin Core metadata format. The heterogeneity of Internet health resources led the CISMeF team to enhance the MeSH thesaurus with the introduction of two new concepts, respectively, resource types and metaterms. CISMeF resource types are a generalization of the publication types of medline. A resource type describes the nature of the resource and MeSH keyword/qualifier pairs describe the subject of the resource. A metaterm is generally a medical specialty or a biological science, which has semantic links with one or more MeSH keywords, qualifiers and resource types. The CISMeF terminology is exploited for several tasks: resource indexing performed manually, resource categorization performed automatically, visualization and navigation through the concept hierarchies and information retrieval using the Doc'CISMeF search engine. The CISMeF health gateway uses several MeSH thesaurus enhancements to optimize information retrieval, hierarchy navigation and automatic indexing.  相似文献   

Gender,Science, and Scientific Organizations in Germany     

Fuchs S  Stebut J  Allmendinger J 《Minerva》2001,39(2):175-201

This article considers the situation of women in science in Germany. We argue that scientific organizations play a crucial role in shaping science careers, often with different consequences for men and women. To sustain the argument, we offer a study of the careers of male and female scientists in the Max Planck Society. Our findings show that external support increases career options and opportunities for men, but not for women scientists.  相似文献