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This, the 39th issue of Transactions on Large-Scale Data- and Knowledge-Centered Systems, contains extended and revised versions of seven papers selected from the 37 contributions presented at the 28th International Conference on Database and Expert Systems Applications, DEXA 2017, held in Lyon, France, in August 2017. Topics covered include knowledge bases, clustering algorithms, parallel frequent itemset mining, model-driven engineering, virtual machines, recommendation systems, and federated SPARQL query processing.

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Querying Interlinked Data by Bridging RDF Molecule Templates.- A Package-to-Group Recommendation Framework.- Statistical Relation Cardinality Bounds in Knowledge Bases.- ETL Environment in the Era of Variety.- eVM: An Event Virtual Machine Framework.- Interactive Exploration of Subspace Clusters on Multicore Processors.- MapFIM+: Memory Aware Parallelized Frequent Itemset Mining in Very Large Datasets.

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