James J. Kennedy

WebCom: A Web Based Volunteer Computer

The World Wide Web has become the largest single possible source of processing power. By coupling CPU time donated by volunteers, researchers and industry have the ability to execute applications that traditionally were in the domain of the supercomputer users. This paper presents one such attempt at creating a system capable of exploiting this abundance of processing power. It is based on an inherently parallel model of computing. The concepts behind computational model are explained and the implementation details are illustrated. The paper presents results obtained from various tests of this implementation.

An Evolution of the WebCom Metacomputer

Functional enhancements to the WebCom metacomputer are described which give rise to dynamic reconfigurability and extendability of the computer platform. Component modules and interactions are described, with particular attention to the communications module that enables dynamic reconfigurability. The machines of the metacomputer can be configured to act in client/server or peer to peer mode on a number of interconnection topologies such as NOWs, Clusters or Grids. This paper addresses the dynamically extendable machine structure of WebCom facilitated by this new communications structure.

WebCom-G: Middleware To Hide The Grid

Current Grid enabling technologies consist of stand-alone architectures. A typical architecture provides middleware access to various services at different hierarchical levels. Services exposed at these levels may be leveraged by the application programmer. However, the level at which the service appears in the hierarchy determines both its richness and the complexity of its use. Thus, benefits gained by using these services are defined by the manner in which they are accessed. Generally, choosing to use a particular service inclines the application programmer to use the associated middleware suite as it is difficult to cherry-pick services across middlewares. Interoperability and independent service access are not easily facilitated in current middlewares. If it is accepted that Grid computing will be an important technology in the near to long term (indeed it can be credibly argued that it is already a very important technology to a select few), then wide spread acceptance will depend on making that technology easily accessible to general exploitation. In practice, this will not only involve interoperability and inclusiveness of key features, but, most importantly, it will require that non specialists be facilitated in constructing grid independent applications that run efficiently on the dynamic architecture that constitutes the Grid. The original problems of programming parallel and distributed systems still hold true: they are notoriously hard to program, since programmers usually have responsibility for synchronizing processes and for resource management. Solutions must be developed to free programmers from the low level details whose consideration gives rise to these problems. In effect, grid programming environments must evolve to a point where grid (and, in general, parallel) programs are freed from architecture details such as data locality, machine availability, inter-task synchronisation, communication topologies, task load-balancing, and fault tolerance in the same manner as present day sequential programmers are freed from explicit memory management, disk access protocols and process scheduling. At that point in the evolution of the Grid, the grid middleware will adopt the character of a grid operating system and many, if not all, of the issues that make grid programming difficult will migrate out of grid application programs. When this is achieved, the vision of hiding the Grid will have been realised and exploitation of the technology can begin in earnest.

Fault tolerance in the WebCom metacomputer

This paper addresses fault tolerance in the WebCom metacomputer. WebComs computation platform is dynamically reconfigurable and volunteer-based. Since its constituent machines may join and leave unpredictability, fault survival and efficient fault recovery is of paramount importance. A fault tolerance mechanism is outlined, which relies on a fast and efficient processor replacement procedure. It is shown that the characteristics of this procedure, together with the hierarchical and referentially transparent nature of WebCom executions, can be used to limit the effect of a fault to its immediate neighbourhood.

CG3DR: Coordination of icosahedral virus reconstruction using Condensed Graphs

We present a visual executable workflow for the three-dimensional reconstruction of icosahedral virus structure using the Traditional Model (TM) method. This workflow is implemented using WebCom, a metacomputer platform based on the Condensed Graph (CG) model. The CG model allows the application to be constructed with a structure that closely mirrors an abstract description of the workflow. By utilising WebComs Integrated Development Environment, we also create a workbench environment that facilitates construction of related workflows through the reuse of components developed for the TM workflow. As an example of this component reuse, we outline the construction of a workflow for the alternative Unbiased Model reconstruction method. In addition, we demonstrate that using a separate machine for the coordination of such workflows results in improved execution times.