1. Introduction
With rapid growth of mobile devices such as PDAs and smart phones, the techniques of mobile computing are becoming important and popular in recent years. The applications of mobile computing conduct the research issues to pervasive computing and ubiquitous computing. Context-aware computing is also one of the research fields and domains in mobile computing. A context-aware system is a mobile environment in which applications can discover and make use of context information including user location, time, date, nearby devices and other environmental activities to adapt their operations and behavior [6]. Due to the fast development of wireless communication on mobile devices, different kinds of context-aware architectures were designed and employed for a wide spectrum of applications. [2] However, since the individual focus of each framework on its specific application domain, the current context-aware systems are heterogeneous in all aspects, such as hardware, mobile resources, operating systems, application software, and platforms. The serious heterogeneous characteristics of context-aware computing are especially important and become significant drawbacks while developing or integrating context-aware services for the applications in mobile computing environments.