PoK

Authors: Gruia-Catalin Roman, Christine Julien, Jamie Payton

Description:
Context-aware computing refers to a computing paradigm in which the behavior of individual components is determined by the circumstances in which they find themselves to an extent that greatly exceeds the typical system/environment interaction pattern common to most modern computing. The environment has an exceedingly powerful impact on a particular application component either because the latter needs to adapt in response to changing external conditions or because it relies on resources whose availability is subject to continuous change. In this paper we seek to develop a systematic understanding of the quintessential nature of context-aware computing by constructing a formal model and notation for expressing context-aware computations. We start with the basic premise that, in its most extreme form, context should be made manifest in a manner that is highly local in appearance and decoupled in fact. Furthermore, we assume a notion of context that is relative to the needs of each individual component, and we xpect context-awareness to be maintained in a totally transparent manner with minimal programming eort. We construct the model from first principles, seek to root our decisions in these formative assumptions, and make every effort to preserve minimality of concepts and elegance of notation.

Authors: Christine Julien, Jamie Payton, Gruia-Catalin Roman

Description:
The increased pervasiveness of wireless mobile computing devices draws new attention to the need for coordination among small networked components. The very nature of the environment requires devices to interact opportunistically when resources are available. Such interactions occur unpredictably as mobile agents generally have no advance knowledge of other agents they will encounter over the lifetime of the application. In addition, as the ubiquity of communicating mobile devices increases, the number of application agents supported by the network grows drastically. Managing access control is crucial to such systems, and application agents must directly manipulate and examine access policies because the agents require full control over their data. However, because these networks are often decoupled from a fixed infrastructure, reliance on centralized servers for authentication and access policies is impractical. In this paper, we explore the essential features of general access control policies tailored to the needs of agent coordination in the presence of physical and logical mobility. This access mechanism derives much of its flexibility and expressiveness from its ability to take into account context information. We propose and evaluate novel constructs to support such policies, especially in the presence of large numbers of highly dynamic application agents.

Authors: Gregory Hackmann, Christine Julien, Jamie Payton, Gruia-Catalin Roman

Description:
In context-aware computing, applications’ behavior is driven by a continually-changing environment. Mobile computing poses unique challenges to context-sensitive applications and middleware, including the ability to run on resource-poor devices like PDAs and the necessity to limit assumptions about the network. Though middlewares exist to provide context-awareness to applications, they do not address the limitations inherent in dynamic mobile environments. This paper discusses a lightweight approach to context-sensitivity that takes into account these considerations.We explore the use of modularization to tailor service discovery policies for applications, as well as leveraging existing language constructs to simplify creation and aggregation of dierent context types. We also discuss an implementation of these concepts, along with three sample applications that can automatically propagate changes in context to clients running on devices from mobile phones to desktop computers.

Authors: RAJEEV ALUR, THOMAS A. HENZINGER, GERARDO LAFFERRIERE, GEORGE J. PAPPAS

Description:
A hybrid system is a dynamical system with both discrete and continuous state changes. For analysis purposes, it is often useful to abstract a system in a way that preserves the properties being analyzed while hiding the details that are of no interest. We show that interesting classes of hybrid systems can be abstracted to purely discrete systems while preserving all properties that are definable in temporal logic. The classes that permit discrete abstractions fall into two categories. Either the continuous dynamics must be restricted, as is the case for timed and rectangular hybrid systems, or the discrete dynamics must be restricted, as is the case for o-minimal hybrid systems. In this paper, we survey and unify results from both areas.