George Coulouris

PerDiS: Design, Implementation, and Use of a PERsistent DIstributed Store

The PerDis (Persisent Distributed Store) project addresses the issue of providing support for distributed collaborative engineering applications. We describe the design and implementation of the PerDis platform, and its support for such applications. Collaborative engineering raises system issues related to the sharing of large volumes of fine-grain, complex objects across wide-area networks and administrative boundaries. PerDiS manages all these aspects in a well defined, integrated, and automatic way. Distributed application programming is simplified because it uses the same memory abstraction as in the centralized case. Porting an existing centralized program written in C or C++ is usually a matter of a few, well-isolated changes. We present some performance results from a proof-of-concept platform that runs a number of small, but real, distributed applications on Unix and Windows NT. These confirm that the PerDiS abstraction is well adapted to the targeted application area and that the overall performance is promising compared to alternative approaches.

An Architecture for Interactive Context-Aware Applications

The interactive behavior of context-aware applications depends on the physical and logical context in which the interaction occurs. The main difference between traditional HCI design and context-aware design is how we deal with context. In this article, we pick up on recent ubicomp community trends, drawing from sociology and focusing on interactions communicative aspects. So, starting from the premise that interaction is communication, we propose a new interaction model for context-aware applications. We then derive an architectural framework that developers can use to implement our interaction model. The main benefit of our architecture is that, by modeling context in the user interface, developers can represent the applications inferences visually for users

Sharing objects over the Internet: the Mushroom approach

This paper reports on the Mushroom project. The project is developing a software framework for collaborative working and user interaction on the Internet. The paper illustrates some of the required features in the context of an application scenario and outlines those aspects of the Mushroom system architecture that support the sharing of information. The projects motivation is to address the problems of coordinated user interaction, distribution and privacy. Mrooms are interactive environments for groups of collaborating users. They provide a shared space in which users are aware of one another while working on shared objects. Their boundaries provide a triggering mechanism for consistency and privacy checks. In contrast to other systems with room-based metaphors, Mushroom focuses on a scalable and flexible system architecture using replicated state, group communication and event-based updates.

Middleware Support for Context-Aware Multimedia Applications

We describe QoSDREAM, a middleware framework for the construction and management of context-aware multimedia applications. The contributions of QoSDREAM include (1) a novel approach to the handling of location data derived from sensors in the physical world which integrates sensor data from a variety of sources into streams of application-relevant events and (2) a component-based architecture for the construction of real-time multimedia and other context-aware applications. The component architecture supports the construction of application models that are used for quality of service analysis and management purposes. Working distributed applications are derived from the models.

A QoS support framework for dynamically reconfigurable multimedia applications

The use of multimedia in distributed systems has begun to include such complex and mission-critical domains as digital television production, ‘video-ondemand’ services, medical and security systems. These applications impose more stringent requirements on the support mechanisms provided by underlying networks and operating systems than most currently deployed continuous media applications. This paper describes the Djinn multimedia programming framework, which is designed to support the construction and dynamic reconfiguration of distributed multimedia applications. We motivate the benefits of a runtime model of the quality of service and other characteristics of multimedia applications, and demonstrate a generic algorithm for scheduling dynamic reconfigurations that maintains QoS guarantees. QoS characteristics are modelled as piecewise-linear or quadratic relations, which are solved using standard constraint programming techniques. During reconfigurations, updates to active components are scheduled so as to maintain temporal constraints on the media streams. We illustrate our approach using experimental results from a real-world application domain.

Dynamically reconfiguring multimedia components: a model-based approach

Distributed multimedia systems are potentially subject to frequent and ongoing evolution of application structures. In such systems it is often unacceptable for reconfigurations to fail or to only partially succeed. This paper describes the reconfiguration architecture of the DJINN multimedia programming framework. We introduce the concept of multimedia transactions for structuring changes into atomic units that preserve application consistency and extend these with the smoothness condition to maintain temporal as well as data integrity across reconfigurations. We present a technique for scheduling configuration changes that trades off the perceived level of smoothness against the available resources and the desired timeliness of the reconfiguration.

Profiling energy use in households and office spaces

Energy consumption is largely studied in the context of different environments, such as domestic, corporate, industrial, and public sectors. In this paper, we discuss two environments, households and office spaces, where people have an especially strong impact on energy demand and usage. We describe an energy monitoring system which supports continuous and tailored energy feedback, and assess the level of information (energy awareness) that can be gained from time-series energy profiles. Our studies pointed to similarities between households and office spaces and motivated us to profile energy in the same way for both settings. As result, an individualized energy metric is introduced which assists (a) public sharing of energy use, (b) aggregation and combination of energy use across different environments, and (c) comparison among individuals.

Liveware: a new approach to sharing data in social networks

Abstract While most schemes that support information sharing on computers rely on formal protocols, in practice much cooperative work takes place using informal means of communication, even chance encounters. This paper proposes a new method of enabling information sharing in loosely-coupled socially-organized systems, typically involving personal rather than institutional computers and lacking the network infrastructure that is generally taken for granted in distributed computing. It is based on the idea of arranging for information transmission to take place as an unobtrusive side-effect of interpersonal communication. Update conflicts are avoided by an information ownership scheme. Under mild assumptions, we show how the distributed database satisfies the property of observational consistency. The new idea, called “Liveware”, is not so much a specific piece of technology as a fresh perspective on information sharing that stimulates new ways of solving old problems. Being general, it transcends particular distribution technologies. A prototype database, implemented in HyperCard and taking the form of an electronic directory, utilizes the medium of floppy disk to spread information in a (benign!) virus-like manner.

Role and task-based access control in the PerDiS groupware platform

A roleand task-based access control scheme has been developed for use in a class of activities that entail cooperation between principals in a virtual enterprise (VE). Data ownership is associated with the component organisations of a VE, each of which constitutes a trust domain. The role/task model was chosen to meet the requirement for a generic access control scheme independent of application code. The model has been implemented for a software platform that provides shared access to clusters of replicated distributed objects. Implications arising from the integration of the access control model with a data replication scheme are discussed.

Visually interactive location-aware computing

The physical disappearance of the computer, associated with Ubicomp, has led to a number of interaction challenges. Due to the lack of an interface users are losing control over applications running in Ubicomp environments. Furthermore, the limited ability for these applications to provide feedback makes it difficult for users to understand their workings and dependencies. We investigate whether an interaction paradigm, based on the visualising location-aware applications on a head-mounted display, is feasible and whether it has the potential to improve the user experience in the same way graphical user interfaces did for the desktop. We show the feasibility of the idea by building an Augmented Reality interface to a location-aware environment. Initial user trials indicate that the user experience can be improved through in-situ visualisation.