Abstract
Coordination in R eo emerges from the composition of the behavioural constraints of the primitives, such as channels, in a component connector. Understanding and implementing R eo, however, has been challenging due to interaction of the channel metaphor, which is an inherently local notion, and the non-local nature of constraint propagation imposed by composition. In this paper, the channel metaphor takes a back seat, and we focus on the behavioural constraints imposed by the composition of primitives, and phrase the semantics of R eo as a constraint satisfaction problem. Not only does this provide a clear intensional description of the behaviour of R eo connectors in terms of synchronisation and data flow constraints, it also paves the way for new implementation techniques based on constraint propagation and satisfaction. In fact, decomposing R eo into constraints provides a new computational model for connectors, which we extend to model interaction with an unknown external world beyond what is currently possible in R eo.

Abstract
The ability to interactively render dynamic scenes with global illumination is one of the main challenges in computer graphics. The improvement in performance of interactive ray tracing brought about by significant advances in hardware and careful exploitation of coherence has rendered the potential of interactive global illumination a reality. However, the simulation of complex light transport phenomena, such as diffuse interreflections, is still quite costly to compute in real time. In this paper we present a caching scheme, termed Instant Caching, based on a combination of irradiance caching and instant radiosity. By reutilising calculations from neighbouring computations this results in a speedup over previous instant radiosity-based approaches. Additionally, temporal coherence is exploited by identifying which computations have been invalidated due to geometric transformations and updating only those paths. The exploitation of spatial and temporal coherence allows us to achieve superior frame rates for interactive global illumination within dynamic scenes, without any precomputation or quality loss when compared to previous methods; handling of lighting and material changes are also demonstrated.

Abstract
This paper describes a study conducted at the University of Nottingham, whose goal was to assess whether the students registered on the first-year module "Mathematics for Computer Scientists" appreciate the calculational method. The study consisted of two parts: "Proof Reading" and "Problem Solving". The goal of "Proof Reading" was to determine what the students think of calculational proofs, compared with more conventional ones, and which are easier to verify; we also assessed how their opinions changed during the term. The purpose of "Problem Solving" was to determine if the methods taught have influenced the students' problem-solving skills. Frequent criticisms of our approach are that we are too formal and that the emphasis on syntactic manipulation hinders students' understanding. Nevertheless, the results show that most students prefer or understand better the calculational proofs. On the other hand, regarding the problem-solving questions, we observed that, in general, the students maintained their original solutions. © 2009 Crown.

Abstract
Shared-nothing clusters are a well known and cost-effective approach to database server scalability, in particular, with highly intensive read-only workloads typical of many 3-tier web-based applications. The common reliance oil a centralized component and a simplistic propagation strategy employed by mainstream solutions however conduct to poor scalability with traditional on-line transaction processing (OLTP), where the Update ratio is high. Such approaches also pose in additional obstacle to high availability while introducing a single point Of failure. More recently, database replication protocols based on group communication have been shown to overcome such limitations, expanding the applicability of shared-nothing Clusters to more demanding transactional workloads. These take simultaneous advantage of total order multicast and transactional semantics to improve oil mainstream solutions. However, none has already been widely deployed in a general purpose database management system. In this paper, we argue that it major hurdle for their acceptance is that these proposals have disappointing performance with specific subsets of real-world workloads. Such limitations are deep-rooted and working around them requires in-depth understanding of protocols and changes to applications. We address this issue with a novel protocol that combines multiple transaction execution mechanisms and replication techniques and then show how it avoids the identified pitfalls. Experimental results are obtained with it workload based oil the industry standard TPC-C benchmark.

Abstract

Abstract
Adaptation of system parameters is acknowledged as a requirement to scalable and dependable distributed systems. Unfortunately, adaptation cannot be effective when provided solely by individual system components as the correct decision is often tied to the composition itself and the system as a whole. In fact, proper adaption is a cross-cutting issue: Diagnostic and feedback operations must target multiple components and do it at different abstraction levels. We address this problem with the SERPENTINE middleware platform. By relying on the industry standard JMX as a service interface, it can monitor and operate on a wide range of distributed middleware and application components. By building on a JMX-enabled OSGi runtime, SERPENTINE is able to control the life-cycle of components themselves. The scriptable stateless server and cascading architecture allow for increased dependability and flexibility.