The LNCS journal Transactions on Large-Scale Data- and Knowledge-Centered Systems focuses on
data management knowledge discovery and knowledge processing which are core and hot topics
in computer science. Since the 1990s the Internet has become the main driving force behind
application development in all domains. An increase in the demand for resource sharing across
different sites connected through networks has led to an evolution of data- and
knowledge-management systems from centralized systems to decentralized systems enabling
large-scale distributed applications providing high scalability. Current decentralized systems
still focus on data and knowledge as their main resource. Feasibility of these systems relies
basically on P2P (peer-to-peer) techniques and the support of agent systems with scaling and
decentralized control. Synergy between grids P2P systems and agent technologies is the key to
data- and knowledge-centered systems in large-scale environments. This volume the 21st issue
of Transactions on Large-Scale Data- and Knowledge-Centered Systems focuses on Data
Warehousing and Knowledge Discovery from Big Data and contains extended and revised versions
of eight papers selected as the best papers from the 14th International Conference on Data
Warehousing and Knowledge Discovery (DaWaK 2012) held in Vienna Austria during September 3-6
2012. These papers cover several advanced Big Data topics ranging from data cube computation
using MapReduce to multiple aggregations over multidimensional databases from data warehousing
systems over complex energy data to OLAP-based prediction models from extended query engines
for continuous stream analytics to popular pattern mining and from rare pattern mining to
enhanced knowledge discovery from large cross-document corpora.
