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.