Ian Warren

Wisdom, decision support and paradigms of decision making

Many decision support tools have been developed over the last 20 years and, in general, they support what Simon termed substantive rationality. However, such tools are rarely suited to helping people tackle wicked problems, for which a form of procedural rationality is better suited. Procedurally rational approaches have appeared in both management science and computer science, examples being the soft OR approach of cognitive mapping and the design rationale based on IBIS. These approaches are reviewed and the development of Wisdom, a procedurally rational decision support process and accompanying tool, is discussed and evaluated. � 2004 Elsevier B.V. All rights reserved.

A model for dynamic configuration which preserves application integrity

Our approach to dynamic configuration is based on building a model of reconfigurable applications. The model documents applications according to the configuration paradigm and for each component, captures structural constraints and behavioural information. The model presents change administrators with an abstract interface to dynamic configuration management. Change is initiated by submitting a version descriptor to the configuration manager; much of the low-level and error-prone activities of dynamic configuration are automated. Synchronisation of dynamic configuration with the application and management of persistent state are fundamental to preserving an applications integrity. We present our synchronisation mechanism, which adopts atomic operations for both intra- and inter-component computation. The problems of persistent state management are simplified by our synchronisation model. We also expose the difficulties and propose solutions for managing composite components and components whose operations are constrained.

Renaissance: a method to support software system evolution

Legacy systems are often business critical and are associated with high maintenance costs. In this paper, we present an overview of a method, Renaissance, which aims to manage the process of regaining control over such systems. Renaissance supports system evolution by first recovering a stable basis using reengineering, and subsequently continuously improving the system by a stream of incremental changes. In both cases, the extent of evolution is determined by a phase which takes into account of technical, business, and organisational factors. Renaissance defines a process framework, a predefined number of evolution strategies, an information repository, and a generic set of personnel responsibilities. The method can be tailored to the needs of particular projects and organisations, and it is not prescriptive of particular tools and techniques.

Improving QoS for peer-to-peer applications through adaptation

The use of peer-to-peer networks has increased dramatically in recent years. As the power of home computers and Internet access speeds increase, we envisage that an increasingly diverse set of applications will seek to make use of the growing pool of resources available around the edge of the network. We suggest that existing peer-to-peer networks are unable to cater for the diverse demands of future applications. We discuss how adaptation may be used to improve the QoS of existing peer-to-peer networks and introduce an innovative network structure with inherent support for multiple levels of adaptation.

A framework for developing reflective and dynamic P2P networks (RaDP2P)

There has been a significant body of research conducted into various structured and unstructured overlay network protocols. Both paradigms have advantages for specific application domains and researchers are beginning to examine the benefits of using hybridized systems. We hypothesize that resource awareness and adaptation are essential to the efficient exploitation of the resources available on the diverse nodes which compose peer-to-peer networks. To support this, we propose a hybrid peer-to-peer model which uses an unstructured decentralised network layered on top of a structured overlay to provide support for multiple levels of adaptation.

Meta-adaptation in autonomic systems

Autonomic computing aims to make self-healing, self-tuning, self-configuring and self-protecting systems a reality. This self-adaptive behaviour is achieved by carrying out changes upon a system when particular constraints or requirements are not met. Existing work focuses on how to determine when a change is necessary and what that change will be. We argue that the mechanism used to carry out the change is equally important and can determine if the change heals, tunes or protects the system as it was intended to. We present OpenRec, a framework which facilitates autonomic computing where the change mechanism is also self-adapting. Novel features of our work include a clean separation of concerns in the self-adaption process, support for an extensible set of change mechanisms and the use of an evolving knowledge base which guides the change process.

AGnuS: the altruistic Gnutella server

The first generation of peer-to-peer file sharing systems followed the traditional client-server paradigm. However, legality and scalability issues have driven the development of decentralized file sharing protocols; the most popular of these being Gnutella. To date, such systems have been unable to match the quality of service (QoS) offered by centralized architectures. AGnuS improves QoS on Gnutella by increasing file availability, improving network friendliness and increasing file quality. This is achieved by layering caching, load balancing, content-based routing and filtering services on top of the core Gnutella protocol.