Distributed Data Summaries for Approximate Query Processing in PDMS

Evolving from heterogeneous database systems one of the main problems in peer data management systems (PDMS) is distributed query processing. With the absence of global knowledge such strategies have to focus on routing the query efficiently to only those peers that are most likely to contribute to the final result. Using routing indexes is one possibility to achieve this. Since data may change over time these structures have to be updated and maintained which can be very expensive. In this paper, we present a novel kind of routing indexes that enables efficient query routing. Furthermore, we propose a threshold based update strategy that can help to reduce maintenance costs by far. We exemplify the benefit of these indexes using a distributed skyline strategy as an example. Finally, we show how relaxing exactness requirements, that are usually posed on results, can compensate the use of slightly outdated index information