On Monitoring the top-k Unsafe Places

In a city, protecting units like police cars move around and protect places such as banks and residential buildings. Different places may have different requirements in how many protecting units should be nearby. If any place has less protecting units around than it requires, it is an unsafe place. This paper studies the Continuous Top-k Unsafe Places (CTUP) query, which continuously monitors the k least safe places while the protecting units keep sending their location updates to the server. The CTUP query is a novel addition to the family of continuous location-based queries, an emerging area due to the recent advances in dynamic location-aware environments. Solutions to existing continuous location-based queries and to the traditional top-k queries do not apply. This paper proposes two solutions to this new query, the BasicCTUP scheme and the OptCTUP scheme. Experiments are conducted to evaluate the proposed solutions.