This book examines the problem of relevant query answering over the Web
and provides a comprehensive overview of relevant query answering over
streaming and distributed data. In recent years, Web applications that
combine highly dynamic data streams with data distributed over the Web
to provide relevant answers have attracted increasing attention.
Answering in a timely fashion, i.e., reactively, is one of the most
important performance indicators, especially when the distributed data
is evolving. The book proposes a solution that retains a local replica
of the distributed data and offers various maintenance policies to
refresh the replica over time. A limited refresh budget guarantees the
reactiveness of the system. Focusing on stream processing and Semantic
Web, it appeals to scientists and graduate students in the field.