Browsing by Subject "Mobile Computing"

Now showing 1 - 3 of 3

Open Access
An evaluation of real-time transaction management issues in mobile database systems
(Oxford University Press, 1999) Kayan, E.; Ulusoy, Özgür
A critical issue in mobile data management is to respond to real-time data access requirements of the supported application. However, it is difficult to handle real-time constraints in a mobile computing environment due to the physical constraints imposed by the mobile computer hardware and the wireless network technology. In this paper, we present a mobile database system model that takes into account the timing requirements of applications supported by mobile computing systems. We provide a transaction execution model with two alternative execution strategies for mobile transactions and evaluate the performance of the system considering various mobile system characteristics, such as the number of mobile hosts in the system, the handoff process, disconnection, coordinator site relocation and wireless link failure. Performance results are provided in terms of the fraction of real-time requirements that are satisfied.
Open Access
Exploiting data mining techniques for broadcasting data in mobile computing environments
(IEEE, 2002) Saygin, Y.; Ulusoy, Özgür
Mobile computers can be equipped with wireless communication devices that enable users to access data services from any location. In wireless communication, the server-to-client (downlink) communication bandwidth is much higher than the client-to-server (uplink) communication bandwidth. This asymmetry makes the dissemination of data to client machines a desirable approach. However, dissemination of data by broadcasting may induce high access latency in case the number of broadcast data items is large. In this paper, we propose two methods aiming to reduce client access latency of broadcast data. Our methods are based on analyzing the broadcast history (i.e., the chronological sequence of items that have been requested by clients) using data mining techniques. With the first method, the data items in the broadcast disk are organized in such a way that the items requested subsequently are placed close to each other. The second method focuses on improving the cache hit ratio to be able to decrease the access latency. It enables clients to prefetch the data from the broadcast disk based on the rules extracted from previous data request patterns. The proposed methods are implemented on a Web log to estimate their effectiveness. It is shown through performance experiments that the proposed rule-based methods are effective in improving the system performance in terms of the average latency as well as the cache hit ratio of mobile clients.
Open Access
Transmission of continuous query results in mobile computing systems
(Elsevier, 2000) Gök, H. G.; Ulusoy, Özgür
In a mobile computing environment, a user with a wireless connection to the information network can access data via submitting queries to data servers. As 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 (CQ) for which the answer changes as the user moves. The answer to a location-dependent CQ can be provided as a set of tuples [S, 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 the transmission time of these tuples to the user. Transmission time of tuples is critical in the sense that it can have a considerable impact on both the communication overhead imposed on the wireless network and the availability of tuples in case of disconnections. In this paper, we propose three tuple transmission approaches that can be used to determine the transmission time of tuples in the answer set of a location-dependent CQ. We also evaluate the relative performance of the proposed approaches under different settings of environmental parameters. (C) 2000 Elsevier Science Inc. All rights reserved.