XML data sources are gaining popularity in the context of Business Intelligence and On-Line Analytical Processing (OLAP) applications, due to the amenities of XML in representing and managing complex and heterogeneous data. However, XML-native database systems currently suffer from limited performance, both in terms of volumes of manageable data and query response time. Therefore, recent research efforts are focusing on horizontal fragmentation techniques, which are able to overcome the above limitations. However, classical fragmentation algorithms are not suitable to control the number of originated fragments, which instead plays a critical role in data warehouses. In this paper, we propose the use of the K-means clustering algorithm for effectively and efficiently supporting the fragmentation of very large XML data warehouses. We complement our analytical contribution with a comprehensive experimental assessment where we compare the efficiency of our proposal against existing fragmentation algorithms.
In order to fragment XML documents, Ma @cite_45 @cite_46 define a new fragmentation notion, called , which is inspired from the oriented-object databases context. This fragmentation technique splits elements of the input XML document, and assigns a reference to each so-obtained sub-element. References are then added to the (DTD) defining the input XML document. This avoid redundancy and inconsistence problems that could occur due to fragmentation process. Bonifati @cite_6 @cite_42 propose a fragmentation strategy for XML documents that is driven by the so-called . These constraints refer to intrinsic properties of XML trees such as the depth and the width of trees. In order to efficiently fragment the input XML document by means of structural constraint, the proposed strategy exploits heuristics and statistics simultaneously.
@cite_46 @cite_45 @cite_42 @cite_6
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Since the introduction of extensible Markup Language (XML), XML repositories have gained a foothold in many global (and government) organizations, where, e-commerce and e-business models have maturated in handling daily transactional data among heterogeneous information systems in multi-data formats. Due to this, the amount of data available for enterprise decision-making process is increasing exponentially and are being stored and or communicated in XML. This presents an interesting challenge to investigate models, frameworks and techniques for organizing and analyzing such voluminous, yet distributed XML documents for business intelligence in the form of XML warehouse repositories and XML marts. In this paper, we address such an issue, where we propose a view-driven approach for modeling and designing of a Global XML FACT (GxFACT) repository under the MDA initiatives. Here we propose the GxFACT using logically grouped, geographically dispersed, XML document warehouses and Document Marts in a global enterprise setting. To deal with organizations' evolving decision-making needs, we also provide three design strategies for building and managing of such GxFACT in the context of modeling of further hierarchical dimensions and or global document warehouses The world-wide web (WWW) is often considered to be the world's largest database and the eXtensible Markup Language (XML) is then considered to provide its datamodel. Adopting this view we have to deal with a distributed database. This raises the question, how to obtain a suitable distribution design for XML documents. In this paper horizontal and vertical fragmentation techniques are generalised from the relational datamodel to XML. Furthermore, splitting will be introduced as a third kind of fragmentation. Then it is shown how relational techniques for de ning reasonable fragments can be applied to the case of XML. A shovel having a blade and an elongated handle is provided between the ends thereof with a laterally extending enlargement. A resilient pad and cover are placed over and supported by the enlargement and handle. The supported pad acts as a fulcrum when placed on the user's thigh just above the knee. The loaded blade may then be raised by lowering the free handle end with one hand and when the blade is in a sufficiently raised position, the handle may be grasped with the other hand near the blade for carrying or discharging the load from the blade. Fragmentation techniques for XML data are gaining momentum within both distributed and centralized XML query engines and pose novel and unrecognized challenges to the community. Albeit not novel, and clearly inspired by the classical divide et impera principle, fragmentation for XML trees has been proved successful in boosting the querying performance, and in cutting down the memory requirements. However, fragmentation considered so far has been driven by semantics, i.e. built around query predicates. In this paper, we propose a novel fragmentation technique that founds on structural constraints of XML documents (size, tree-width, and tree-depth) and on special-purpose structure histograms able to meaningfully summarize XML documents. This allows us to predict bounding intervals of structural properties of output (XML) fragments for efficient query processing of distributed XML data. An experimental evaluation of our study confirms the effectiveness of our fragmentation methodology on some representative XML data sets.