Yu Jiao

Application of Mobile Agents in Mobile Data Access Systems: A Prototype

Creating a global information-sharing environment in the presence of autonomy and heterogeneity of data sources is a difficult task. When adding mobility and wireless medium to this mix, the constraints on bandwidth, connectivity, and resources worsen the problem. Our past research in global information sharing systems resulted in the design, implementation, and prototype of a search engine, the summary schemas model, which supports imprecise global accesses to the data sources while preserving local autonomy. We extended the scope of our search engine by incorporating mobile agent technology. The use of mobile agents alleviates many problems associated with wireless communication. We devised and implemented the MAMDAS system, which applies mobile agent technology in a mobile data access system framework. As shown by our experimental study, MAMDAS achieved better performance, scalability, portability, and robustness compared to its predecessors.

Adaptive power management for mobile agent-based information retrieval

Mobile agent technology has been used in wireless distributed information retrieval for many years. However, the energy-efficiency issue in such systems remains unexplored. In this paper, we proposed an adaptive application-driven power management (AADPM) protocol for mobile agent-based applications within the IEEE 802.11b infrastructure WLAN environment. Our goal is to minimize energy while achieving low round trip time (RTT) delay. We discuss the protocol and evaluate its effectiveness using the network simulator NS2. We also draw horizontal comparisons among a variety of PM methods reported in the literature. Experimental results show that, compared to the power save mode supported by 802.11b, AADPM reduces the network interface card energy consumption by 65% while only introducing 3% RTT delay.

Mobile Agents in Mobile Data Access Systems

The heterogeneity and geographical distribution of data sources in the presence of autonomy make it a very difficult task to provide global information sharing. When adding mobility and wireless medium to this mix (Mobile Data Access System), the constraints on bandwidth, connectivity, and resources worsen the problem. Application of mobile agent technology in a global information-sharing environment releases the global mobile users from the constraints imposed by the wireless medium and mobile devices.This work applies the Mobile Agent technology in a Mobile Data Access System framework (MAMDAS) using the Summary Schemas Model as the underlying multidatabase platform. This approach provides better performance by reducing the network traffic and higher degree of autonomy by allowing agents to execute without the owners interference. As witnessed by our experimental results, the MAMDAS exhibits the following advantages compared to the first SSM prototype: ? It is about 6 times faster. ? It supports larger number of concurrent queries. ? It demonstrates greater scalability, portability, and robustness.

Security Issues and Solutions in Distributed Heterogeneous Mobile Database Systems

Security continues to be a fundamental requirement of modern computer systems. As more information is stored electronically, users become more concerned with the security of their information. Designing secure systems is a difficult problem, complicated by the distributed nature of modern systems—communication links are now both wired and wireless and information is shared among autonomous and heterogeneous sources. Once the system is deployed, security threats and attacks must be evaluated and handled throughout its life cycle, as attackers discover and exploit vulnerabilities. This chapter considers the security problem within the context of centralized databases and multidatabases as well as mobile systems. The techniques employed to create a secure centralized database system can be extended to meet the security needs of multidatabase systems. This extension is not trivial, however. Many issues must be considered so that the needs of each component are met. When wireless communication links and mobility are introduced, adapting existing methods may not provide a satisfactory solution. Generally, security is expensive in terms of communication, processing, and storage overhead, which translates into increased power consumption. This overhead is unacceptable in mobile systems because mobile devices are already resource-poor. Therefore, new techniques, which draw from existing technologies and the lessons learned from their deployment, must be designed to handle the constraints introduced by mobile systems.

Adaptive application-driven WLAN power management

In this paper we present an adaptive application-driven power management (AADPM) strategy with online idle period length distribution learning capability for the IEEE 802.11b WLAN. We discuss its design and evaluate the performance in comparison with other power management strategies using the network simulator NS2. We simulated both the single user and multiple user scenarios. Experimental results have shown that, compared with other power management methods examined in this paper, AADPM achieved the highest energy saving in all cases and it demonstrated strong adaptability to network congestion.

On the Content Predictability of Cooperative Image Caching in Ad Hoc Networks

Emerging applications of mobile data management, such as content-based image retrieval in ad hoc networks, require the awareness of content distribution to enact and optimize the communication and search tasks. Caching is a widely used approach in mobile environments to improve system performance and keep track of replications. Within the scope of mobile and ubiquitous computing infrastructure, traditional caching techniques are not effective for large-size data such as images due to the limitations of bandwidth, storage, and power. The functionality of caching techniques relies on exact match, making them unsuitable for imprecise and similarity-based queries. In addition, the description of cached contents is defined based on the query context instead of data content, which fails to exploit the semantic locality of cached data and makes the traditional caching techniques inefficient in utilizing cache storage. In this paper, we present a semantic-aware caching scheme (SAIC) for image databases in ad hoc networks. The proposed scheme is designed based on several novel ideas: 1) multi-level partitioning of semantic space, 2) constraint-based representation of image semantics, 3) non-flooding query resolution, and 4) adaptive cache consistency maintenance. Our combination of theoretical analysis and simulation show the efficiency of the proposed scheme, and evaluate its performance in comparison against two ad hoc caching schemes as advanced in the literature.

Mobile agents and energy-efficient multidatabase design

Multidatabase systems are widely used to integrate distributed heterogeneous data sources. To support mobile data access, existing multidatabases must address the obstacles in mobile computing such as low bandwidth, intermittent network connections, and resource constraints of mobile devices. The execution autonomy of mobile agents alleviates these problems and provides opportunity for conserving energy. We proposed and implemented a novel multidatabase information retrieval system, MAMDAS, which represents an application of Mobile Agents within the Mobile Data Access System framework. In this paper, we propose several MAMDAS optimization techniques to improve its performance and study the effect of mobile agents on energy saving through extensive simulation. Our experimental results show that by deploying appropriate power management policies, the mobile device energy saving can achieve as high as 51%. The high performance, energy efficiency, scalability, and robustness of MAMDAS allow us to envision its application in a variety of fields such as military operations, emergency teams, and mobile e-business.

Transaction Processing in Mobile, Heterogeneous Database Systems

The rapid explosion in the use of wireless devices, combined with the simultaneous infrastructure expansion required to suport a massive number of users, has made ubiquitous access to data a reality. When a large number of users simultaneously accesses global data in a mobile computing environment, an efficient means to manage a large amount of concurrent transactions is required. Current multi-database concurrency control schemes do not address the limited bandwidth and frequent disconnections associated with wireless networks. This article describes a new hierarchical concurrency control algorithm, v-lock, that addresses the shortcomings of existing multi-database concurrency control schemes. The algorithm uses global locking tables created with semantic informantion contained within a hierarchy to serialize global transactions, and remove global deadlocks. Additionally, wireless transmission of data is subject to weak or frequent disconnection. With the increased amount of local memory available at the mobile unit, data replication can be used to provide local data availability, limiting the restrictions imposed by a wireless mobile environment. In a mobile, multi-database environment, local autonomy restrictions prevent the use of a page-or-file-based data replication scheme. This article describes a new data replication scheme to address to limited bandwidth and local autonomy restrictions. Consistency is maintained by using a parity-based invalidation scheme of data cached at the mobile unit. Additionally, a simple prefetching scheme is used to further improve the effectiveness of the proposed scheme. Finally, simulated results of the concurrency control and replication algorithms are presented and discussed. Keywords: mobile database; ubiquitous; transaction processing; concurrency control; caching and prefetching; replication

Online adaptive application-driven WLAN power management

In this paper we present an adaptive application-driven power management (AADPM) strategy with online idle period length distribution learning capability for the IEEE 802.11b WLAN. We discuss its design and evaluate the performance in comparison with other power management strategies using the network simulator NS2. We simulated both the single user and multiple users scenarios. Experimental results have shown that, compared with other power management methods examined in this paper, AADPM achieved the highest energy saving in all cases and demonstrated strong adaptability to network congestion