152 research outputs found
An environment for workflow applications on wide-area distributed systems
©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Workflow techniques are emerging as an important approach for the specification and management of complex processing tasks. This approach is especially powerful for utilising distributed data and processing resources in widely-distributed heterogeneous systems. We describe our DISCWorld distributed workflow environment for composing complex processing chains, which are specified as a directed acyclic graph of operators. Users of our system can formulate processing chains using either graphical or scripting tools. We have deployed our system for image processing applications and decision support systems. We describe the technologies we have developed to enable the execution of these processing chains across wide-area computing systems. In particular, we present our Distributed Job Placement Language (based on XML) and various Java interface approaches we have developed for implementing the workflow metaphor. We outline a number of key issues for implementing a high-performance, reliable, distributed workflow management system.James, H.A.; Hawick, K.A.; Coddington, P.D
A reconfigurable component-based problem solving environment
©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Problem solving environments are an attractive approach to the integration of calculation and management tools for various scientific and engineering applications. These applications often require high performance computing components in order to be computationally feasible. It is therefore a challenge to construct integration technology, suitable for problem solving environments, that allows both flexibility as well as the embedding of parallel and high performance computing systems. Our DISCWorld system is designed to meet these needs and provides a Java-based middleware to integrate component applications across wide-area networks. Key features of our design are the abilities to: access remotely stored data; compose complex processing requests either graphically or through a scripting language; execute components on heterogeneous and remote platforms; reconfigure task sub-graphs to run across multiple servers. Operators in task graphs can be slow (but portable) “pure Java” implementations or wrappers to fast (platform specific) supercomputer implementations.K. Hawick, H. James, P. Coddingto
On-line data archives
©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.Digital libraries and other large archives of electronically retrievable and manipulable material are becoming widespread in both commercial and scientific arenas. Advances in networking technologies have led to a greater proliferation of wide-area distributed data warehousing with associated data management challenges. We review tools and technologies for supporting distributed on-line data archives and explain our key concept of active data archives, in which data can be, processed on-demand before delivery. We are developing wide-area data warehousing software infrastructure for geographically distributed archives of large scientific data sets, such as satellite image data, that are stored hierarchically on disk arrays and tape silos and are accessed by a variety of scientific and decision support applications. Interoperability is a major issue for distributed data archives and requires standards for server interfaces and metadata. We review present activities and our contributions in developing such standards for different application areas.K. Hawick, P. Coddington, H. James, C. Patte
High Performance Fortran and Possible Extensions to support Conjugate Gradient Algorithms
We evaluate the High-Performance Fortran (HPF) language for the compact expression and efficient implementation of conjugate gradient iterative matrix-solvers on High Performance Computing and Communications(HPCC) platforms. We discuss the use of intrinsic functions, data distribution directives and explicitly parallel constructs to optimize performance by minimizing communications requirements in a portable manner. We focus on implementations using the existing HPF definitions but also discuss issues arising that may influence a revised definition for HPF-2. Some of the codes discussed are available on the World Wide Web at http://www.npac.syr.edu/hpfa/ alongwith other educational and discussion material related to applications in HPF
Von-Neumann's and related scaling laws in Rock-Paper-Scissors type models
We introduce a family of Rock-Paper-Scissors type models with symmetry
( is the number of species) and we show that it has a very rich structure
with many completely different phases. We study realizations which lead to the
formation of domains, where individuals of one or more species coexist,
separated by interfaces whose (average) dynamics is curvature driven. This type
of behavior, which might be relevant for the development of biological
complexity, leads to an interface network evolution and pattern formation
similar to the ones of several other nonlinear systems in condensed matter and
cosmology.Comment: 5 pages, 6 figures, published versio
Junctions and spiral patterns in Rock-Paper-Scissors type models
We investigate the population dynamics in generalized Rock-Paper-Scissors
models with an arbitrary number of species . We show, for the first time,
that spiral patterns with -arms may develop both for odd and even , in
particular in models where a bidirectional predation interaction of equal
strength between all species is modified to include one N-cyclic predator-prey
rule. While the former case gives rise to an interface network with Y-type
junctions obeying the scaling law , where is the
characteristic length of the network and is the time, the later can lead to
a population network with -armed spiral patterns, having a roughly constant
characteristic length scale. We explicitly demonstrate the connection between
interface junctions and spiral patterns in these models and compute the
corresponding scaling laws. This work significantly extends the results of
previous studies of population dynamics and could have profound implications
for the understanding of biological complexity in systems with a large number
of species.Comment: 6 pages, 8 figures, published versio
Coexistence and Survival in Conservative Lotka-Volterra Networks
Analyzing coexistence and survival scenarios of Lotka-Volterra (LV) networks in which the total biomass is conserved is of vital importance for the characterization of long-term dynamics of ecological communities. Here, we introduce a classification scheme for coexistence scenarios in these conservative LV models and quantify the extinction process by employing the Pfaffian of the network's interaction matrix. We illustrate our findings on global stability properties for general systems of four and five species and find a generalized scaling law for the extinction time
GraphCombEx: A Software Tool for Exploration of Combinatorial Optimisation Properties of Large Graphs
We present a prototype of a software tool for exploration of multiple
combinatorial optimisation problems in large real-world and synthetic complex
networks. Our tool, called GraphCombEx (an acronym of Graph Combinatorial
Explorer), provides a unified framework for scalable computation and
presentation of high-quality suboptimal solutions and bounds for a number of
widely studied combinatorial optimisation problems. Efficient representation
and applicability to large-scale graphs and complex networks are particularly
considered in its design. The problems currently supported include maximum
clique, graph colouring, maximum independent set, minimum vertex clique
covering, minimum dominating set, as well as the longest simple cycle problem.
Suboptimal solutions and intervals for optimal objective values are estimated
using scalable heuristics. The tool is designed with extensibility in mind,
with the view of further problems and both new fast and high-performance
heuristics to be added in the future. GraphCombEx has already been successfully
used as a support tool in a number of recent research studies using
combinatorial optimisation to analyse complex networks, indicating its promise
as a research software tool
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