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This, the 28th issue of Transactions on Large-Scale Data- and Knowledge-Centered Systems, contains extended and revised versions of six papers presented at the 26th International Conference on Database- and Expert-Systems Applications, DEXA 2015, held in Valencia, Spain, in September 2015. Topics covered include efficient graph processing, machine learning on big data, multistore big data integration, ontology matching, and the optimization of histograms for the Semantic Web.

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Accelerating Set Similarity Joins Using GPUs.- Divide-and-Conquer Parallelism for Learning Mixture Models.- Multistore Big Data Integration with CloudMdsQL.- Ontology Matching with Knowledge Rules.- Regularized Cost-Model Oblivious Database Tuning with Reinforcement Learning.- Workload-Aware Self-tuning Histograms for the Semantic Web.

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