Location-dependent spatial query containment

Nowadays, location-related information is highly accessible to mobile users via issuing Location-Dependent Spatial Queries (LDSQs) with respect to their locations wirelessly to Location-Based Service (LBS) servers. Due to the limited mobile device battery energy, scarce wireless bandwidth, and heavy LBS server workload, the number of LDSQs submitted over wireless channels to LBS servers for evaluation should be minimized as appropriate. In this paper, we exploit query containment techniques for LDSQs (called LDSQ containment) to enable mobile clients to determine whether the result of a new LDSQ Q′ is completely covered by that of another LDSQ Q previously answered by a server (denoted by Q′ ⊆ Q) and to answer Q′ locally if Q′ ⊆ Q. Thus, many LDSQs can be reduced from server evaluation. To support LDSQ containment, we propose a notion of containment scope, which represents a spatial area corresponding to an LDSQ result wherein all semantically matched LDSQs are answerable with the result. Through a comprehensive simulation, our proposed approach significantly outperforms existing techniques.