Contory: A Middleware for the Provisioning of Context Information on Smart Phones

Context-awareness can serve to make ubiquitous applications deployed for mobile devices adaptive, personalized, and accessible in dynamically changing environments. Unfortunately, existing approaches for the provisioning of context information in ubiquitous computing environments rarely take into consideration the resource constraints of mobile devices and the uncertain availability of sensors and service infrastructures. This paper presents the design, prototype implementation, and experimental evaluation of Contory, a middleware specifically designed to accomplish efficient context provisioning on mobile devices. To make context provisioning flexible and adaptive based on dynamic operating conditions, Contory integrates multiple context provisioning strategies, namely internal sensors-based, external infrastructure-based, and distributed provisioning in ad hoc networks. Applications can request context information provided by Contory using a declarative query language which features on-demand, periodic, and event-based context queries. Experimental results obtained in a testbed of smart phones demonstrate the feasibility of our approach and quantify the cost of supporting context provisioning in terms of energy consumption.