Context-aware systems offer entirely new opportunities for application developers and for end users by gathering context data and adapting systems behavior accordingly. Especially in combination with mobile devices these mechanisms are of high value and are used to increase usability tremendously. In this pap er, we present common architecture principles of context-aware systems and derive a layered conceptual design framework to explain the different elements common to most context-aware architectures. Based on these design principles, we introduce various existing context-aware systems focusing on context-aware middleware and frameworks, which ease the development of context-aware applications. We discuss various approaches and analyze important aspects in context-aware computing on the basis of the presented systems.

Abstract. Policies are being increasingly used for automated system management and controlling the behavior of complex systems, allowing administrators to modify system behavior without changing source code or requiring the consent or cooperation of the components being governed. Past approaches to policy representation have been restrictive in many ways. By way of contrast, semantically-rich policy representations can reduce human error, simplify policy analysis, reduce policy conflicts, and facilitate interoperability. In this paper, we compare three approaches to policy representation, reasoning, and enforcement. We highlight similarities and differences between Ponder, KAoS, and Rei, and sketch out some general criteria and properties for more adequate approaches to policy semantics in the future. 1

This document describes a new architecture that exploits Semantic Web technologies for supporting pervasive context-aware systems. This architecture called Context Broker Architecture (CoBrA) differs from other architectures in using the Web Ontology Language OWL for modeling ontologies of context and for supporting context reasoning. Central to our architecture is a broker agent that maintains a shared model of context for all computing entities in the space and enforces the privacy policies defined by the users when sharing their contextual information. We describe the use of CoBrA, its associated ontologies, and its privacy protection mechanism in an intelligent meeting room prototype.

Trust is an important tool in human life, as it enables people to cope with the uncertainty caused by the free will of others. Uncertainty and uncontrollability are also issues in computer-assisted collaboration and electronic commerce in particular. A computational model of trust and its implementation can alleviate this problem. This survey

Many types of information available in a pervasive computing environment, such as people location information, should be accessible only by a limited set of people. Some properties of the information raise unique challenges for the design of an access control mechanism: Information can emanate from more than one source, it might change its nature or granularity before reaching its final receiver, and it can flow through nodes administrated by different entities. We propose three design principles for the architecture of an access control mechanism: (1) extract pieces of information in raw data streams early, (2) define policies controlling access at the information level, and (3) exploit information relationships for access control. We describe an example architecture in which we apply these principles. We also report how our earlier work about adding access control to a people location service contributed to the more general access control architecture proposed here.

Semantic Web Services enable the dynamic discovery of services based on a formal, explicit specification of the requester needs. The actual Web Services that will be used to satisfy the requester's goal are selected at run-time and, therefore, they are not known beforehand. As a consequence, determining whether the selected services can be trusted becomes an essential issue. In this paper, we propose the use of the Peertrust language to decide if trust can be established between the requester and the service provider. We add modelling elements to the Web Service Modeling Ontology (WSMO) in order to include trust information in the description of Semantic Web Services. In this scenario, we discuss different registry architectures and their implications for the matchmaking process. In addition, we present a matching algorithm for the trust policies introduced.

Abstract. Over the past five years, the MyCampus group at Carnegie Mellon University has been developing and experimenting with Ambient Intelligence technologies aimed at enhancing everyday life. The project has drawn on multiple areas of expertise, combining the development of an open Semantic Web infrastructure for context-aware service provisioning with an emphasis on issues of privacy and usability. In this paper, we review key motivations behind the project, discuss the MyCampus Semantic Web infrastructure and report on our experience tailoring the architecture for different environments (e.g. everyday campus life applications, office applications, museum tour guide). This includes a discussion of Semantic e-Wallets aimed at reconciling user demands for context awareness and privacy as well as a description of different context-aware applications developed and evaluated during the course of the project. We also discuss our experience using Case-Based Reasoning (CBR) functionality developed to overcome usability issues associated with capturing complex, context-sensitive user preferences. The paper concludes with a summary of lessons learned so far and of challenges still to be addressed.

Abstract. Policies are being increasingly used for controlling the behavior of complex multi-agent systems. The use of policies allows administrators to regulate agent behavior without changing source code or requiring the consent or cooperation of the agents being governed. However, policy-based control can sometimes encounter difficulties when applied to agents that act in pervasive environments characterized by frequent and unpredictable changes. In such cases, we cannot always specify policies a priori to handle any operative run time situation, but instead require continuous adjustments to allow agents to behave in a contextually appropriate manner. To address these issues, some policy approaches for governing agents in pervasive environments specify policies in a way that is both context-based and semantically-rich. Two approaches have been used in recent research: an ontology-based approach that relies heavily on the expressive features of Description Logic (DL) languages, and a rule-based approach that encodes policies as Logic Programming (LP) rules. The aim of this paper is to analyze the emerging directions for the specification of semantically-rich context-based policies, highlighting their advantages and drawbacks. Based on our analysis we describe a hybrid approach that exploits the expressive capabilities of both DL and LP approaches. 1.

Computing is moving toward a pervasive context-aware environment in which agents with limited resources will require external support to help them become context-aware. In this paper, we describe an agent based architecture called Context Broker Architecture (CoBrA) to help these agents to acquire, reason about and share context knowledge. A key component in our architecture is an explicit context ontology defined using the Web Ontology Language (OWL). This ontology models the basic concepts of people, agents, places, and presentation events. We also describe a use case scenario and prototype design of CoBrA in an intelligent meeting room environment.

Abstract. Wireless connectivity and widespread diffusion of portable devices offer novel opportunities for users to share resources anywhere and anytime, and to form ad-hoc coalitions. Resource access control is crucial to leverage these ad-hoc collaborations. In pervasive scenarios, however, collaborating entities cannot be predetermined and resource availability frequently varies, even unpredictably, due to user/device mobility, thus complicating resource access control. Access control policies cannot be defined based on entity’s identities/roles, as in traditional access control solutions, or be specified a priori to face any operative run time condition, but require continuous adjustments to adapt to the current situation. To address these issues, this paper advocates the adoption of novel access control policy models that follow two main design guidelines: context-awareness to control resource access on the basis of context visibility and to enable dynamic adaptation of policies depending on context changes, and semantic technologies for context/policy specification to allow high-level description and reasoning about context and policies. The paper also describes the design of a semantic context-aware policy model that adopts ontologies and rules to express context and context-aware access control policies and supports policy adaptation. 1