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This paper proposes a middleware architecture for the automated, real-time, unsupervised annotation of lowlevel context features and their mapping to high-level semantics. The distinguishing characteristic of this architecture is that both low level components such as sensors, feature extraction algorithms and data sources, and high level components such as application-specific ontologies are pluggable to the middleware architecture thus facilitating application development and system configuration to different real-world scenarios. A prototype implementation based on Semantic Web tools is presented in depth, while the benefits and drawbacks of this approach are underlined. We argue that the use of Semantic Web provides powerful answers to context awareness challenges. Furthermore, it enables the composition of simple rules through human-centric interfaces, which may launch a context-aware system that will annotate content without the need for user technical expertise. A test case of system operation in a laboratory environment is presented. Emphasis is given, along with the theoretical justification, to practical issues that arise in real-world scenarios.

Abstract-This paper presents a lightweight approach for providing web-based location aware multimedia content retrieval through Java enabled handheld devices. The main distinguishing characteristic of the proposed approach is that it separates the positioning system from the content access mechanisms, while being generic to the selection of the localization technology, i.e. GPS, Bluetooth, etc. Furthermore, it is built as an open, standards-based, modular architecture comprising a core of reusable components and interfaces for supporting different types of services, through web technologies. On-site services are provided through smart phones, which exploit the user's contextual state, mainly defined as end-user location and organization of points of interest. A test case of a museum e-guidance application for Bluetooth enabled smart phones is presented. The test case demonstrates the capacity of the approach to provide location based content retrieval to museum visitors while using their personal phones, without the need for the visitors, or the museum, to acquire and manage specially built user terminals, e.g. PDAs with GPS modules.

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This article presents the AVATON system. AVATON aims at providing citizens with ubiquitous user-friendly services, offering personalized, location-aware (GSM Association, 2003), tourism-oriented multimedia information related to the area of the Aegean Volcanic Arc. Towards this end, a uniform architecture is adopted in order to dynamically release the geographic and multimedia content to the end users through enhanced application and network interfaces, targeting different device technologies (mobile phones, PDAs, PCs, and TV sets). Advanced positioning techniques are applied for those mobile user terminals that support them.