P103 - BTW2007 - Datenbanksysteme in Business, Technologie und Web
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- KonferenzbeitragÜberlegungen zur Entwicklung komplexer Grid-Anwendungen mit Globus Toolkit(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Walter, Andreas; Böhm, Klemens; Schosser, StephanVerteilte Anwendungen mit einem hohen Ressourcenbedarf lassen sich heutzutage mit Hilfe von Grid-Techniken ohne den Einsatz großer Rechenzentren erstellen. Stattdessen nutzt man freie Ressourcen auf Computern, die im Internet verteilt sind. Grid Middleware ist hierfür eine Grundlage. Hauptinteresse dieser Arbeit ist die Analyse der am weitesten verbreiteten Middleware für Grid-Anwendungen, dem Globus Toolkit. Uns geht es insbesondere um die Erstellung von komplexen Anwendungen mit hohem Ressourcenbedarf. Für unsere Untersuchung haben wir als geeignete Anwendung Web-Crawling ausgewählt, aufgrund eines sehr hohen Daten- und Kontrollaufwands über viele verteilt arbeitende Knoten. Wir zeigen, welche Anforderungen dabei an Globus Toolkit gestellt werden, und wie gut sich diese Plattform für solche Anwendungen eignet.
- KonferenzbeitragChange Management in Large Information Infrastructures – Representing and Analyzing Arbitrary Metadata(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Stumm, Boris; Dessloch, StefanWith information infrastructures getting more and more complex, it becomes necessary to give automated support for managing the evolution of the infrastructure. If changes are detected in a single system, the potential impact on other systems has to be calculated and appropriate countermeasures have to be initiated to prevent failures and data corruption that span several systems. This is the goal of Caro, our approach to change impact analysis in large information infrastructures. In this paper we present how we model the metadata of information systems to make a global analysis possible, regardless of the data models used, and how the analysis process works.
- KonferenzbeitragA Classification of Schema Mappings and Analysis of Mapping Tools(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Legler, Frank; Naumann, FelixSchema mapping techniques for data exchange have become popular and useful tools both in research and industry. A schema mapping relates a source schema with a target schema via correspondences, which are specified by a domain expert possibly supported by automated schema matching algorithms. The set of correspondences, i.e., the mapping, is interpreted as a data transformation usually expressed as a query. These queries transform data from the source schema to conform to the target schema. They can be used to materialize data at the target or used as views in a virtually integrated system. We present a classification of mapping situations that can occur when mapping between two relational or nested (XML) schemata. Our classification takes into con- sideration 1:1 and n:m correspondences, attribute-level and higher-level mappings, and special constructs, such as choice constraints, cardinality constraints, and data types. Based on this classification, we have developed a general suite of schemata, data, and correspondences to test the ability of tools to cope with the different mapping situations. We evaluated several commercial and research tools that support the definition of schema mappings and interpret this mapping as a data transformation. We found that no tool performs well in all mapping situations and that many tools produce incorrect data transformations. The test suite can serve as a benchmark for future improvements and developments of schema mapping tools.
- KonferenzbeitragAlgebraic Query Optimization for Distributed Top-k Queries(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Neumann, Thomas; Michel, SebastianDistributed top-k query processing is increasingly becoming an essential functionality in a large number of emerging application classes. This paper addresses the efficient algebraic optimization of top-k queries in wide-area distributed data repositories where the index lists for the attribute values (or text terms) of a query are distributed across a number of data peers and the computational costs include network latency, bandwidth consumption, and local peer work. We use a dynamic programming approach to find the optimal execution plan using compact data synopses for selectivity estimation that is the basis for our cost model. The optimized query is executed in a hierarchical way involving a small and fixed number of communication phases. We have performed experiments on real web data that show the benefits of distributed top-k query optimization both in network resource consumption and query response time.
- KonferenzbeitragThe Information Integrator: using Semantic Technology to provide a single view to distributed data(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Angele, Jürgen; Gesmann, MichaelFor the integration of data that resides in autonomous data sources Software AG uses ontologies. Data source ontologies describe the data sources themselves. Business ontologies provide an integrated view of the data. FLogic rules are used to describe mappings between data objects in data source or business ontologies. Furthermore, FLogic is used as the query language. FLogic rules are perfectly suited to describe the mappings between objects and their properties. Some of these mapping rules can be generated automatically from the data sources metadata. Some patterns do frequently reoccur in user-defined mapping rules, for instance rules which establish inverse object relations or rules which create new object relations based on the objects’ property values. Within our first project access to information is still typical data retrieval and not so much knowledge inference. Therefore, a lot of effort in this project concentrated on query functionality and even more on performance. But these are only first steps. To strengthen this development and to get more experience in this field Software AG recently joined several EU research projects which all have a focus on exploitation of semantic technology with concrete business cases.
- KonferenzbeitragAlgorithms for merged indexes(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Graefe, Goetz
- KonferenzbeitragPathfinder: XQuery Compilation Techniques for Relational Database Targets(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Teubner, JensRelational database systems are highly efficient hosts to table-shaped data. It is all the more interesting to see how a careful inspection of both, the XML tree structure as well as the W3C XQuery language definition, can turn relational databases into fast and scalable XML processors. This work shows how the deliberate choice of a relational tree encoding makes the XML data model—ordered, unranked trees—accessible to relational database systems. Efficient XPath-based access to these data is enabled in terms of staircase join, a join operator that injects full tree awareness into the relational database kernel. A loop-lifting compiler translates XQuery expressions into purely algebraic query plans. The representation of iteration (i.e., the XQuery FLWOR construct) in terms of set-oriented algebra primitives forms the core of this compiler. Together, the techniques we describe lead to unprecedented XQuery evaluation scalability in the multi-gigabyte XML range. Pathfinder is an open-source implementation of a purely relational XQuery processor.
- KonferenzbeitragGetting Prime Cuts from Skylines over Partially Ordered Domains(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Balke, Wolf-Tilo; Güntzer, Ulrich; Siberski, WolfSkyline queries have recently received a lot of attention due to their intuitive query formulation: users can state preferences with respect to several attributes. Unlike numerical preferences, preferences over discrete value domains do not show an inherent total order, but have to rely on partial orders as stated by the user. In such orders typically many object values are incomparable, increasing the size of skyline sets significantly, and making their computation expensive. In this paper we explore how to enable interactive tasks like query refinement or relevance feedback by providing 'prime cuts'. Prime cuts are interesting subsets of the full Pareto skyline, which give users a good overview over the skyline. They have to be small, efficient to compute, suitable for higher numbers of query predicates, and representative. The key to improved performance and reduced result set sizes is the relaxation of Pareto semantics to the concept of weak Pareto dominance. We argue that this relaxation yields intuitive results and show how it opens up the use of efficient and scalable query processing algorithms. Assessing the practical impact, our experiments show that our approach leads to lean result set sizes and outperforms Pareto skyline computations by up to two orders of magnitude.
- KonferenzbeitragEfficient Reverse k-Nearest Neighbor Estimation(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Achtert, Elke; Böhm, Christian; Kröger, Peer; Kunath, Peter; Pryakhin, Alexey; Renz, MatthiasThe reverse k-nearest neighbor (RkNN) problem, i.e. finding all objects in a data set the k-nearest neighbors of which include a specified query object, has received increasing attention recently. Many industrial and scientific applications call for solutions of the RkNN problem in arbitrary metric spaces where the data objects are not Euclidean and only a metric distance function is given for specifying object similarity. Usually, these applications need a solution for the generalized problem where the value of k is not known in advance and may change from query to query. In addition, many applications require a fast approximate answer of RkNN-queries. For these scenarios, it is important to generate a fast answer with high recall. In this paper, we propose the first approach for efficient approximative RkNN search in arbitrary metric spaces where the value of k is specified at query time. Our approach uses the advantages of existing metric index structures but proposes to use an approximation of the nearest-neighbor-distances in order to prune the search space. We show that our method scales significantly better than existing non-approximative approaches while producing an approximation of the true query result with a high recall.
- KonferenzbeitragIntegrating Structural Joins into a Tuple-Based XPath Algebra(Datenbanksysteme in Business, Technologie und Web (BTW 2007) – 12. Fachtagung des GI-Fachbereichs "Datenbanken und Informationssysteme" (DBIS), 2007) Mathis, ChristianOver the recent years, very little effort has been made to give XPath a proper algebraic treatment. The only laudable exception is the Natix Algebra (NAL) which defines the translation of XPath queries into algebraic expressions in a concise way, thereby enabling algebraic optimizations. However, NAL does not capture various promising core XML query evaluation algorithms like, for example, the Holistic Twig Join. By integrating a logical structural join operator, we enable NAL to be compiled into a physical algebra, containing exactly those missing physical operators. We will provide several important query unnesting rules and demonstrate the effectivity of our approach by an implementation in the XML Transaction Coordinator (XTC)—our prototype of a native XML database system.