ALBERT

Description: research

Description: research

Description: This paper reports on the results of an independent evaluation of the techniques presented in the VLDB 2007 paper "Scalable Semantic Web Data Management Using Vertical Partitioning", authored by D. Abadi, A. Marcus, S. R. Madden, and K. Hollenbach [1]. We revisit the proposed benchmark and examine both the data and query space coverage. The benchmark is extended to cover a larger portion of the query space in a canonical way. Repeatability of the experiments is assessed using the code base obtained from the authors. Inspired by the proposed vertically-partitioned storage solution for RDF data and the performance figures using a column-store, we conduct a complementary analysis of state-of-the-art RDF storage solutions. To this end, we employ MonetDB/SQL, a fully-functional open source column-store, and a well-known -- for its performance -- commercial row-store DBMS. We implement two relational RDF storage solutions -- triple-store and vertically-partitioned -- in both systems. This allows us to expand the scope of [1] with the performance characterization along both dimensions -- triple-store vs. vertically-partitioned and row-store vs. column-store -- individually, before analyzing their combined effects. A detailed report of the experimental test-bed, as well as an in-depth analysis of the parameters involved, clarify the scope of the solution originally presented and position the results in a broader context by covering more systems.

Description: By leveraging modern networking hardware (RDMA-enabled network cards), we can shift priorities in distributed database processing significantly. Complex and sophisticated mechanisms to avoid network traffic can be replaced by a scheme that takes advantage of the bandwidth and low latency offered by such interconnects. We illustrate this phenomenon with cyclo-join, an efficient join algorithm based on continuously pumping data through a ring-structured network. Our approach is capable of exploiting the resources of all CPUs and distributed main-memory available in the network for processing queries of arbitrary shape and datasets of arbitrary size.

Description: This paper presents our experiences in porting the Sloan Digital Sky Survey(SDSS)/ SkyServer to the state-of- the-art open source database system MonetDB/SQL. SDSS acts as a well-documented benchmark for scientific database management. We have achieved a fully functional prototype for the personal SkyServer, to be downloaded from our site. The lessons learned are 1) the column store approach of MonetDB demonstrates a great potential in the world of scientific databases. However, the application also challenged the functionality of our implementation and revealed that a fully operational SQL environment is needed, e.g. including persistent stored modules; 2) the initial performance is competitive to the reference platform, MS SQL Server 2005, and 3) the analysis of SDSS query traces hints at several techniques to boost performance by utilizing repetitive behavior and zoom-in/zoom-out access patterns, that are currently not captured by the system.

Description: Stream applications gained significant popularity over the last years that lead to the development of specialized stream engines. These systems are designed from scratch with a different philosophy than nowadays database engines in order to cope with the stream applications requirements. However, this means that they lack the power and sophisticated techniques of a full fledged database system that exploits techniques and algorithms accumulated over many years of database research. In this paper, we take the opposite route and design a stream engine directly on top of a database kernel. Incoming tuples are directly stored upon arrival in a new kind of system tables, called baskets. A continuous query can then be evaluated over its relevant baskets as a typical one-time query exploiting the power of the relational engine. Once a tuple has been seen by all relevant queries/operators, it is dropped from its basket. A basket can be the input to a single or multiple similar query plans. Furthermore, a query plan can be split into multiple parts each one with its own input/output baskets allowing for flexible load sharing query scheduling. Contrary to traditional stream engines, that process one tuple at a time, this model allows batch processing of tuples, e.g., query a basket only after x tuples arrive or after a time threshold has passed. Furthermore, we are not restricted to process tuples in the order they arrive. Instead, we can selectively pick tuples from a basket based on the query requirements exploiting a novel query component, the basket expressions. We investigate the opportunities and challenges that arise with such a direction and we show that it carries significant advantages. We propose a complete architecture, the DataCell, which we implemented on top of an open-source column-oriented DBMS. A detailed analysis and experimental evaluation of the core algorithms using both micro benchmarks and the standard Linear Road benchmark demonstrate the potential of this new approach.

Description: Landslide activity often significantly alters the spectral signal of the earth surface through the displacement and disruption of the surficial vegetation layer. This makes landslide areas targets for detection and mapping from spaceborne data. We employed data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) to detect and map landslides that were triggered by the 2005 Kashmir earthquake. Digital Elevation Models (DEMs) generated from ASTER stereo data, together with DEM data from the Shuttle Radar Topography Mission (SRTM) were used to calculate volume estimates for individual landslides. Orthophotos and DEMs were generated from corrected level 1B data. Orientation of the 3N and corresponding 3B band from GCPs, transformation to epipolar geometry, parallax-matching, and parallax-to-DEM conversion was done using the PCI Geomatica 10.1 Orthoengine software. Orthophotos and DEMs were then integrated into a GIS (ArcGIS 9.2), where landslides were automatically detected and mapped using different band thresholds, band ratios, change detection methods and selected terrain information. The resulting landslides inventory data was used to supplement and extend an existing field data inventory.

Description: Dieser Artikel diskutiert den Charakter von Pollentypen. Wir argumentieren, dass Pollentypen und Pflanzentaxa komplett unterschiedliche Entitäten (morphologische bzw. taxonomische) sind, und deswegen unterschiedlich behandelt und dargestellt werden sollten. Allgemeine Probleme der konventionellen Nomenklatur von Pollentypen werden anhand von Beispielen aus der europäischen palynologischen Praxis illustriert. Wir plädieren für Deutlichkeit in der Nomenklatur von Pollentypen und für die wissenschaftliche Freiheit, ‘unkonventionelle‘ Methoden zu benutzen, um Verwirrung zu vermeiden.

Description: research

Description: Detailed knowledge about the thermal properties of rocks containing gas hydrate is required in order to quantify processes involving the formation and decomposition of gas hydrate in nature. This work investigates the influence of methane hydrate on the transport of heat in hydrate-bearing rocks. Both the thermal conductivity of gashydrate bearing sediments and the thermal effects of phase transitions are analyzed. In the framework of the Mallik 2002 program three wells penetrating a continental gas hydrate occurrence under permafrost were successfully equipped with permanent fiberoptic distributed temperature sensing cables. Temperature data were collected over a period of 21 months after completion of the wells. The analysis of the disturbed well temperatures after drilling revealed a strong effect of phase transitions on temperature changes. For the first time, the effects of induced temperature changes within a gas hydrate deposit were monitored in-situ. The resulting temperature gradient anomalies could be successfully utilized to determine the base of the gas hydrate occurrences and the permafrost layer at about 1103-1104±3.5 m and 599-604±3.5 m below ground level respectively. At the end of the 21-month observation period, the well temperature returned close to equilibrium with the formation temperature. At the base of the gas hydrate occurrences a temperature of 12.3 ◦C was measured, which is about 0.7 K below the stability temperature predicted by thermodynamic calculations considering a pressure gradient of 10.12 kPa m〈sup〉−1〈/sup〉 and a sea-water salinity of 35 ppt. Under the stated conditions, the base of the stability zone of methane hydrate at Mallik would lie at about 1140 m below ground level. Thermal conductivity profiles were calculated from the geothermal data as well as from a petrophysical model derived from the available logging data and application of mixing-law models. The results indicate, that variations of thermal conductivity are mainly lithologically controlled with a minor influence from hydrate saturation. The results of the geometric mean model showed the best agreement to the thermal conductivity profiles derived from geothermal data. Average thermal conductivity values of the hydrate-bearing intervals range between 2.35 W m〈sup〉−1〈/sup〉 K〈sup〉−1〈/sup〉 and 2.77 W m〈sup〉−1〈/sup〉 K〈sup〉−1〈/sup〉 . A simplified numerical model of conductive heat flow was set up in order to assess the temperature effect of phase transitions within the gas hydrate bearing strata. Within the model the mobilization of latent heat during the phase transition was considered (enthalpy method), taking into account the stability conditions for methane hydrate at Mallik (pressure, temperature, pore fluid and gas phase composition) as well as effects of hydrate decomposition on the thermal rock properties. The modelling results indicate, that the regeneration of hydrate after the recovery of stability conditions is inhibited.

Description: thesis