Karen Henricksen

A survey of context modelling and reasoning techniques

Development of context-aware applications is inherently complex. These applications adapt to changing context information: physical context, computational context, and user context/tasks. Context information is gathered from a variety of sources that differ in the quality of information they produce and that are often failure prone. The pervasive computing community increasingly understands that developing context-aware applications should be supported by adequate context information modelling and reasoning techniques. These techniques reduce the complexity of context-aware applications and improve their maintainability and evolvability. In this paper we discuss the requirements that context modelling and reasoning techniques should meet, including the modelling of a variety of context information types and their relationships, of situations as abstractions of context information facts, of histories of context information, and of uncertainty of context information. This discussion is followed by a description and comparison of current context modelling and reasoning techniques.

Modeling Context Information in Pervasive Computing Systems

As computing becomes more pervasive, the nature of applications must change accordingly. In particular, applications must become more flexible in order to respond to highly dynamic computing environments, and more autonomous, to reflect the growing ratio of applications to users and the corresponding decline in the attention a user can devote to each. That is, applications must become more context-aware. To facilitate the programming of such applications, infrastructure is required to gather, manage, and disseminate context information to applications. This paper is concerned with the development of appropriate context modeling concepts for pervasive computing, which can form the basis for such a context management infrastructure. This model overcomes problems associated with previous context models, including their lack of formality and generality, and also tackles issues such as wide variations in information quality, the existence of complex relationships amongst context information and temporal aspects of context.

Developing context-aware pervasive computing applications: Models and approach

There is growing interest in the use of context-awareness as a technique for developing pervasive computing applications that are flexible, adaptable, and capable of acting autonomously on behalf of users. However, context-awareness introduces a variety of software engineering challenges. In this paper, we address these challenges by proposing a set of conceptual models designed to support the software engineering process, including context modelling techniques, a preference model for representing context-dependent requirements, and two programming models. We also present a software infrastructure and software engineering process that can be used in conjunction with our models. Finally, we discuss a case study that demonstrates the strengths of our models and software engineering approach with respect to a set of software quality metrics.

A software engineering framework for context-aware pervasive computing

There is growing interest in the use of context-awareness as a technique for developing pervasive computing applications that are flexible, adaptable, and capable of acting autonomously on behalf of users. However, context-awareness introduces various software engineering challenges, as well as privacy and usability concerns. In this paper, we present a conceptual framework and software infrastructure that together address known software engineering challenges, and enable further practical exploration of social and usability issues by facilitating the prototyping and fine-tuning of context-aware applications.

Modelling and using imperfect context information

Most recently developed context-aware software applications make unrealistic assumptions about the quality of the available context information, which can lead to inappropriate actions by the application and frustration on the part of the user. Here, we explore the problem of imperfect context information and some of its causes, and propose a novel approach for modelling incomplete and inaccurate information. Additionally, we present a discussion of our experiences in developing a context-aware communication application, highlighting design issues that are pertinent when developing applications that rely on imperfect context information.

Middleware for distributed context-aware systems

Context-aware systems represent extremely complex and heterogeneous distributed systems, composed of sensors, actuators, application components, and a variety of context processing components that manage the flow of context information between the sensors/actuators and applications. The need for middleware to seamlessly bind these components together is well recognised. Numerous attempts to build middleware or infrastructure for context-aware systems have been made, but these have provided only partial solutions; for instance, most have not adequately addressed issues such as mobility, fault tolerance or privacy. One of the goals of this paper is to provide an analysis of the requirements of a middleware for context-aware systems, drawing from both traditional distributed system goals and our experiences with developing context-aware applications. The paper also provides a critical review of several middleware solutions, followed by a comprehensive discussion of our own PACE middleware. Finally, it provides a comparison of our solution with the previous work, highlighting both the advantages of our middleware and important topics for future research.

Experiences in Using CC/PP in Context-Aware Systems

Future pervasive systems will be based on ubiquitous, often mobile, interconnected devices supporting mobile users in their computing tasks. These systems need to be context-aware in order to cope with highly dynamic environments. In this paper, we present a context model and a context management system able to support a pervasive system infrastructure. This context model is based on the CC/PP standard proposed to support content negotiation between Web browsers and servers. We have defined a set of CC/PP components and attributes that allow to express a variety of context information types and relationships between context descriptions. The paper discusses pros and cons of using CC/PP as a basis for a context model and a context management system.

Context obfuscation for privacy via ontological descriptions

Context information is used by pervasive networking and context-aware programs to adapt intelligently to different environments and user tasks. As the context information is potentially sensitive, it is often necessary to provide privacy protection mechanisms for users. These mechanisms are intended to prevent breaches of user privacy through unauthorised context disclosure. To be effective, such mechanisms should not only support user specified context disclosure rules, but also the disclosure of context at different granularities. In this paper we describe a new obfuscation mechanism that can adjust the granularity of different types of context information to meet disclosure requirements stated by the owner of the context information. These requirements are specified using a preference model we developed previously and have since extended to provide granularity control. The obfuscation process is supported by our novel use of ontological descriptions that capture the granularity relationship between instances of an object type.

Adapting the Web interface: an adaptive Web browser

The growing number of mobile computing devices with diverse characteristics creates a requirement for seamless (device independent) access to computing resources of distributed systems. One of the most common applications in distributed systems is the Web browser, which is not only used to access resources on the Internet but also as an interface to many information system applications. The authors address types of adaptation that can be applied to a Web browser in response to diverse context changes, including changes in available computing resources, input and output device capabilities, network characteristics, location and use context. We also present a design and implementation of a Web browser that adapts to changes in its network and computing environment by exploiting context metadata.

Context privacy and obfuscation supported by dynamic context source discovery and processing in a context management system

The extensive context information collection abilities of ubiquitous computing environments represent a significant threat to user privacy. In this paper we address this threat by introducing a context information privacy mechanism. Our approach relies on context-dependent ownership definitions and context owner-specified privacy preferences to control context disclosure to third-parties. These privacy preferences enable context owners to stipulate not only to whom their context information can be disclosed and the conditions of disclosure, but also the level of detail at which the context information can be disclosed. Context information that cannot be disclosed at its existing level of detail is obfuscated to meet detail level requirements stipulated by its owner. To achieve this obfuscation of context information we introduce a new approach based on dynamic discovery and processing of context sources. Our new approach is demonstrated in a Context Management System in which context source discovery and processing is facilitated by the SensorML sensor description standard being developed by the Open Geospatial Consortium.