Processing of continuous queries from moving objects in mobile computing systems

Abstract

Recent advances in computer hardware technology and wireless communication networks have led to the emergence of mobile computing systems. In a mobile computing environment, a user with a wireless connection to the information network can access data via submitting queries to the data server. Since the mobility is the most distinguishing feature of the mobile computing paradigm, location becomes an important piece of information for the so called location-dependent queries where the answer to a query depends on the current location of the user who issued the query. A location-dependent query submitted by a mobile user can become more difficult to process when it is submitted as a continuous query for which the answer changes as the user moves. The answer to a location-dependent continuous query is a set that consists of tuples < 5', begin, end > indicating that object S is the answer of the query from time begin to time end. Once the tuples in the answer set are determined, the next step is to determine when to send these tuples to the user. The transmission time of the tuples is critical in the sense that it can affect the communication overhead imposed on the wireless network and the availability of tuples in case of disconnections. In this thesis, we propose three tuple transmission approaches that determine the transmission time of a tuple in the answer set of a location-dependent continuous query. We also design and implement a simulation model to compare the performance of the proposed tuple transmission approaches under different settings of environmental parameters.