Entwurf und Implementierung eines SQL-normkonformen Datenbankkatalogs für ein relationales Datenbankmanagementsystem     

Steffen Skatulla  Ralf Schaarschmidt  Peter Pistor und Klaus Küspert 《Informatik - Forschung und Entwicklung》2000,15(3):161-170

Zusammenfassung.   Bei relationalen Datenbanksystemen haben sich de-jure-Normen für SQL stetig weiterentwickelt; mit diesen Normen wird es einfacher, portable Datenbankanwendungen zu entwickeln. Die SQL-Norm ruht auf zwei S?ulen, zum einen auf der Datenbanksprache SQL, zum anderen auf einer Vorgabe eines Datenbankkatalogs, welcher die gespeicherten Daten beschreiben soll. Im vorliegenden Beitrag wird derjenige Teilbereich des Datenbankkatalogs der aktuellen SQL99-Norm dargestellt, der bereits in der SQL92-Norm (ISO/IEC 9075:1992 bzw. DIN 66315) definiert ist und die klassischen (nicht objektrelationalen) Elemente einer relationalen Datenbank beschreibt. In dieser Darstellung nimmt der zweischichtige Spezifikationsansatz (Informationsschema, Definitionsschema) einigen Raum ein; mit seiner Hilfe weist SQL einen eleganten Weg, auf dem existierende Datenbanksysteme normkonforme Datenbankkataloge bereitstellen k?nnen. Anhand des Datenbankmanagementsystems DB2 wird anschlie?end untersucht, wie ein normkonformer Datenbankkatalog (das sogenannte Informationsschema) „oberhalb” des verfügbaren DB2-Katalogs realisiert werden kann, d. h. wie die vom Informationsschema geforderten Sichten auf DB2-Katalogtabellen abgebildet werden k?nnen. Auf generelle Schwierigkeiten und M?glichkeiten einer solchen Abbildung (ein- oder zweistufig) wird ebenso eingegangen wie auf Probleme, die sich speziell bei DB2 ergeben. In einer prototypischen Realisierung konnte das Informationsschema bis auf wenige Einschr?nkungen komplett umgesetzt werden. Damit wurde die Machbarkeit normkonformer Kataloge nachgewiesen. In heute verfügbaren DBMS-Produkten sind Datenbankkataloge in dieser konsequent normkonformen Gestalt leider immer noch nicht anzutreffen. Eingegangen am 5. M?rz 1999 / Angenommen am 1. Mai 2000  相似文献   

Using Instrumental Variables to Estimate the Parameters in Unconditional and Conditional Second-Order Latent Growth Models     

Steffen Nestler 《Structural equation modeling》2013,20(3):461-473

This article applies Bollen’s (1996) 2-stage least squares/instrumental variables (2SLS/IV) approach for estimating the parameters in an unconditional and a conditional second-order latent growth model (LGM). First, the 2SLS/IV approach for the estimation of the means and the path coefficients in a second-order LGM is derived. An empirical example is then used to show that 2SLS/IV yields estimates that are similar to maximum likelihood (ML) in the estimation of a conditional second-order LGM. Three subsequent simulation studies are then presented to show that the new approach is as accurate as ML and that it is more robust against misspecifications of the growth trajectory than ML. Together, these results suggest that 2SLS/IV should be considered as an alternative to the commonly applied ML estimator.  相似文献   

The potential of toe flexor muscles to enhance performance     

Jan-Peter Goldmann  Maximilian Sanno  Steffen Willwacher  Kai Heinrich  Gert-Peter Brüggemann 《Journal of sports sciences》2013,31(4):424-433

Abstract

The metatarsal phalangeal joint (MPJ) and its crossing toe flexor muscles (TFM) represent the link between the large energy generating leg extensor muscles and the ground. The purpose of this study was to examine the functional adaptability of TFM to increased mechanical stimuli and the effects on walking, running and jumping performance.

Fifteen men performed a heavy resistance TFM strength training with 90% of the maximal voluntary isometric contraction (MVIC) for 7 weeks (560 contractions) for the left and right foot. Maximal MPJ and ankle plantar flexion moments during MVICs were measured in dynamometers before and after the intervention. Motion analyses (inverse dynamics) were performed during barefoot walking, running, and vertical and horizontal jumping. Athletic performance was determined by measuring jump height and distance.

Left (0.21 to 0.38 Nm · kg^?1; P < 0.001) and right (0.24 to 0.40 Nm · kg^?1; P < 0.001) MPJ plantar flexion moments in the dynamometer, external MPJ dorsiflexion moments (0.69 to 0.75 Nm · kg^?1; P = 0.012) and jump distance (2.25 to 2.31 m; P = 0.006) in horizontal jumping increased significantly.

TFM responded highly to increased loading within a few weeks. The increased force potential made a contribution to an athlete's performance enhancement.  相似文献   

Innovation paths and the innovation performance of low-technology firms—An empirical analysis of German industry     

Eva Kirner  Steffen Kinkel  Angela Jaeger 《Research Policy》2009,38(3):447-458

This paper analyses innovation paths and the innovation performance of low-technology firms in comparison to medium- and high-technology firms. Firstly, it shows that low-, medium- and high-technology sectors consist of a considerable mix of low-, medium- and high-technology firms. Thus, it is necessary to look at the firm level when analysing how innovation patterns differ depending on the level of R&D intensity. Secondly, the product and process innovation performance of low-technology firms in German industry is analysed based on data from 1663 firms in the German Manufacturing Survey 2006, applying a set of both product and process related innovation output indicators. The empirical results show that low-technology manufacturing firms lag behind their medium- and high-tech counterparts regarding their product and service innovation performance, to a large degree on purely definitional grounds, but that they seem to perform equally well and in some respects even better at process innovation.  相似文献   

Approximating Test Statistics Using Eigenvalue Block Averaging     

Njål Foldnes  Steffen Grønneberg 《Structural equation modeling》2018,25(1):101-114

We introduce and evaluate a new class of approximations to common test statistics in structural equation modeling. Such test statistics asymptotically follow the distribution of a weighted sum of i.i.d. chi-square variates, where the weights are eigenvalues of a certain matrix. The proposed eigenvalue block averaging (EBA) method involves creating blocks of these eigenvalues and replacing them within each block with the block average. The Satorra–Bentler scaling procedure is a special case of this framework, using one single block. The proposed procedure applies also to difference testing among nested models. We investigate the EBA procedure both theoretically in the asymptotic case, and with simulation studies for the finite-sample case, under both maximum likelihood and diagonally weighted least squares estimation. Comparison is made with 3 established approximations: Satorra–Bentler, the scaled and shifted, and the scaled F tests.  相似文献   

„Echte Sportler“ — „Gute Soldaten“     

Klaus Cachay  Steffen Bahlke  Helmut Mehl  Michael Krüger 《Sportwissenschaft》2002,32(3):339-344

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Deconstructing Horror: Commodities in the Fiction of Jonathan Carroll and Kathe Koja     

Steffen Hantke 《Journal of American culture (Malden, Mass. : 2003)》1995,18(3):41-57

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Kinetics of elite unilateral below-elbow amputee running     

Franziska Mally  Stefan Litzenberger  Steffen Willwacher  Björn Braunstein  Gert-Peter Brüggemann  Anton Sabo 《Sports Engineering》2016,19(3):185-199

The role of the upper limbs in human locomotion and their influence on ground reaction force (GRF) have been extensively examined for walking and slow running. However, research has focused on unimpaired populations and has not evaluated high-speed running. In this study, the GRFs of an unilateral upper limb amputee athlete [missing right forearm, personal bests (PB): 400 m: 0:48.45 min, 800 m: 1:50.92 min] running at speeds of 5.4 and 8 m/s were collected using four floor-mounted force plates in a 100 m tartan track recording at 1000 Hz. The amputee athlete also performed trials with a running speed of 8 m/s wearing a weighted cuff on his impaired arm (0.5 and 1 kg, respectively). GRF data (without additional weight) were compared to those of an unimpaired athlete with similar PBs and anthropometry (age, height, weight). All data were evaluated for anterior–posterior, medial–lateral and vertical GRF as well as for stance phase (SP) duration and free moment (FM) values and a paired Student-t test (\(\alpha =5\) %) was performed on maximum and minimum values of the respective data sets comparing the left and right side of both athletes with each other, but no intersubjective comparisons were performed. The results revealed that vertical GRF showed significant differences for the impaired athlete at both running speeds comparing left and right foot, whereas the unimpaired athlete showed no significant differences in this matter at all. Medial–lateral GRF showed highly significant differences between the left and right foot of both athletes at both running speeds, whereas the results for anterior–posterior GRF and FM, however, showed ambiguous results. The trials with additional weight on the impaired limb led to significant differences for SP duration, but not for all conditions, and left–right differences did not change with additional weight. GRFs were found to differ in minimum medial–lateral GRF with no and heavy weight, maximum medial–lateral GRF within all weight conditions and maximum vertical GRF with no and heavy weight. For the FM, the overall pattern changed drastically and maximum FM showed a highly significant difference between the left and right foot, but none between the different conditions for both feet. Even though more significant asymmetries could be revealed for the impaired athlete, no general conclusion can be drawn at this point, given the limitations of the here presented study (low number of subjects available, anthropometric data of the impaired athlete could not be assessed).  相似文献   

Numbers matter! The society of indicators,scores and ratings     

Steffen Mau 《International Studies in Sociology of Education》2020,29(1-2):19-37

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A Bayesian Approach for Estimating Multilevel Latent Contextual Models     

Steffen Zitzmann  Oliver Lüdtke  Alexander Robitzsch  Herbert W. Marsh 《Structural equation modeling》2016,23(5):661-679

In many applications of multilevel modeling, group-level (L2) variables for assessing group-level effects are generated by aggregating variables from a lower level (L1). However, the observed group mean might not be a reliable measure of the unobserved true group mean. In this article, we propose a Bayesian approach for estimating a multilevel latent contextual model that corrects for measurement error and sampling error (i.e., sampling only a small number of L1 units from a L2 unit) when estimating group-level effects of aggregated L1 variables. Two simulation studies were conducted to compare the Bayesian approach with the maximum likelihood approach implemented in Mplus. The Bayesian approach showed fewer estimation problems (e.g., inadmissible solutions) and more accurate estimates of the group-level effect than the maximum likelihood approach under problematic conditions (i.e., small number of groups, predictor variable with a small intraclass correlation). An application from educational psychology is used to illustrate the different estimation approaches.  相似文献