“…Top-k queries have attracted much interest in many different areas such as network and system monitoring [8,23], information retrieval [18,22,32,36], sensor networks [34,39], multimedia databases [9,17,31], spatial data analysis [10], P2P systems [3,4], data stream management systems [13,21,27,30], probabilistic databases [33,35,40], temporal databases [26], etc. The main reason for such interest is that they avoid overwhelming the user with large numbers of uninteresting answers, which are resource-consuming.…”