Kerry Raymond

A tree-based algorithm for distributed mutual exclusion

We present an algorithm for distributed mutual exclusion in a computer network of N nodes that communicate by messages rather than shared memory. The algorithm uses a spanning tree of the computer network, and the number of messages exchanged per critical section depends on the topology of this tree. However, typically the number of messages exchanged is O(log N) under light demand, and reduces to approximately four messages under saturated demand. Each node holds information only about its immediate neighbors in the spanning tree rather than information about all nodes, and failed nodes can recover necessary information from their neighbors. The algorithm does not require sequence numbers as it operates correctly despite message overtaking.

Transformation: The Missing Link of MDA

In this paper we explore the issue of transforming models to models, an essential part of the OMGs Model Driven Architecture (MDA) vision. Drawing from the literature and our experiences implementing a number of transformations using different technologies, we explore the strengths and weaknesses of the different technologies and identify requirements for a transformation language for performing the kind of model-to-model transformations required to realise the MDA vision.

Incremental model transformation for the evolution of model-driven systems

Model transformations are an integral part of model-driven development. Incremental updates are a key execution scenario for transformations in model-based systems, and are especially important for the evolution of such systems. This paper presents a strategy for the incremental maintenance of declarative, rule-based transformation executions. The strategy involves recording dependencies of the transformation execution on information from source models and from the transformation definition. Changes to the source models or the transformation itself can then be directly mapped to their effects on transformation execution, allowing changes to target models to be computed efficiently. This particular approach has many benefits. It supports changes to both source models and transformation definitions, it can be applied to incomplete transformation executions, and a priori knowledge of volatility can be used to further increase the efficiency of change propagation.

A distributed algorithm for multiple entries to a critical section

Ricart and Agrawalas algorithm for distributed mutual exclusion is extended to enable up to K nodes to be within the critical section simultaneously. Our algorithm requires at most 2 * (N-1) messages per entry to the critical section, and occasionally fewer.

Dynamic conflict detection in policy-based management systems

While advances in open distributed systems have undoubtedly provided a uniquely diverse environment for users, managing the resources within such an environment has become an increasingly complex task. This challenge has been considered for several years within the distributed systems management research community and we have recently seen policy-based management emerge as one such promising exemplification. The focus of our work has been predominantly on supporting the requirements of large evolving enterprises. Such environments present a significant challenge for policy-based management as the fluidity and complexity of interactions occurring in such environments mean that prevailing static-based specification and analysis of policies and roles, would be inadequate in many instances. We are therefore interested in providing support for a dynamic policy-based management environment. This paper discusses the critical nature of providing both dynamic and static conflict detection and resolution and introduces a scalable computationally-efficient dynamic conflict detection mechanism.

Methods for conflict resolution in policy-based management systems

While developments in distributed object computing environments, such as the Common Object Request Broker Architecture (CORBA) by the Object Management Group (2000) and the Telecommunication Intelligent Network Architecture (TINA) by H. Mulder (2002), have enabled interoperability between domains in large open distributed systems, managing the resources within such systems has become an increasingly complex task. This challenge has been considered for several years within the distributed systems management research community and policy-based management has recently emerged as a promising solution. Large evolving enterprises present a significant challenge for policy-based management partly due to the requirement to support both mutual transparency and individual autonomy between domains according to C. Bidan and V. Issarny (1998), but also because the fluidity and complexity of interactions occurring within such environments requires an ability to cope with the existence of multiple, potentially inconsistent policies. This paper discusses the need for providing both dynamic (run-time) and static (compile-time) conflict detection and resolution for policies in such systems and builds on our earlier conflict detection work (Dunlop et al., 2001, 2002) to introduce the methods for conflict resolution in large open distributed systems.

Reference Model of Open Distributed Processing (RM-ODP): Introduction

The Reference Model of Open Distributed Processing (RM-ODP) was a joint effort by the international standards bodies ISO and ITU-T to develop a coordinating framework for the standardisation of open distributed processing (ODP). The model describes an architecture within which support of distribution, interworking, interoperability and portability can be integrated. The RM-ODP framework defines ODP concerns using five “viewpoints” (abstractions), namely enterprise, information, computational, engineering, and technology. This tutorial introduces the reference model, describing the viewpoints and some of the ODP functions and transparencies.

Model Synchronisation: Definitions for Round-Trip Engineering

In a model-centric software development environment, a multitude of different models are used to describe a software system on different abstraction layers and from different perspectives. Following the MDA vision, model transformation is used to support the gradual refinement from abstract models into more concrete models. However, target models do not stay untouched but may be changed due to maintenance work or evolution of the software. Therefore, in order to preserve a coherent description of the whole system, it is necessary to propagate certain changes to a target model back to the source model. However, as transformations in general are partial and not injective, they cannot be easily reversed to propagate changes. This paper presents a formal definition of round-trip engineering and the semantics of target changes in the context of partial and non-injective transformations.

Supporting business contracts in open distributed systems

Open distributed systems are increasingly used to support business transactions within and across organisations. In order to achieve this goal, fundamental concepts of business practices should be incorporated into a supporting architecture. Support for business contracts can be regarded as an essential ingredient of such an architecture in terms of facilitating more efficient inter-organisational business interactions. This is augmented by the prevailing feeling in business today that global interdependencies are becoming more critical for gaining and maintaining the competitive edge. In this paper we make an initial attempt to identify important contract concepts from economic and legal standpoints and use them to derive a business contract framework. We further discuss how these concepts can be incorporated into an architecture for open distributed processing (ODP).<<ETX>>

Model transformation: a declarative, reusable patterns approach

The MOF (Meta Object Facility) query, view and transformation RFP, issued by OMG will result in a key enabling technology for model-driven development of large distributed systems. We have designed a transformation language which will meet the requirements of this RFP, and several others besides. The language is declarative and patterns based. Transformation descriptions are explicitly reusable and modular. Rules that make up such descriptions may be aspect-driven, allowing for transformations to be written to address semantic concepts rather than structural features. This paper introduces the language and its rationale, and shows how it is used to solve s small but non-trivial MDA problem.