Grid computing is becoming a mainstream technology for large-scale distributed resource sharing and system integration. Workflow management is emerging as one of the most important grid services. In this work, a workflow management system for grid computing, called GridFlow, is presented, including a user portal and services of both global grid workflow management and local grid sub-workflow scheduling. Simulation, execution and monitoring functionalities are provided at the global grid level, which work on top of an existing agent-based grid resource management system. At each local grid, sub-workflow scheduling and conflict management are processed on top of an existing performance prediction based task scheduling system. A fuzzy timing technique is applied to address new challenges of workflow management in a cross-domain and highly dynamic grid environment. A case study is given and corresponding results indicate that local and global grid workflow management can coordinate with each other to optimise workflow execution time and solve conflicts of interest. 1.

Process management is an extremely important concept in both business and scientific communities. Several workflow management tools have been proposed in recent years offering advanced functionality in various domains. In the business world, workflow vendors offer commercial and customized solutions targeting specific users. In the scientific world, several open-source workflow management tools are freely available. However, they are directed toward service aggregation rather than distributed process management. Little consideration is given to the needs of the client in terms of mapping the process flow of the client. In the Grid community it is essential that the Grid users have such a tool available enabling them to orchestrate complex workflows on the fly without substantial help from the service providers. At the same time it is important that the Grid user not be burdened with the intricacies of the workflow system. With the perspective of the Grid user in mind, an extensible client-side workflow management system, called GridAnt, has been developed. This paper discusses the design principles, functionality, and application of the proposed GridAnt workflow manager. 1

In this paper we present the design, prototype implementation and operation of the Accord Composition Engine (ACE) that enables the dynamic and autonomic composition of Grid services. ACE builds on the Open Grid Services Architecture (OGSA) and autonomically synthesizes composition plans, when possible, from an available pool of services based on dynamically defined objectives and constraints. The key contribution is a dynamic composition model based on relational algebra and graph theory.

The Grid is rapidly emerging as the dominant paradigm for wide area distributed application systems. As a result, there is a need for modeling and analyzing the characteristics and requirements of Grid systems and programming models. This paper adopts the well-established body of models for distributed computing systems, which are based upon carefully stated assumptions or axioms, as a basis for defining and characterizing Grids and their programming models and systems. The requirements of programming Grid applications and the resulting requirements on the underlying virtual organizations and virtual machines are investigated. The assumptions underlying some of the programming models and systems currently used for Grid applications are identified and their validity in Grid environments is discussed. A more in-depth analysis of two programming systems, the Imperial College E-Science Networked Infrastructure (ICENI) and Accord, using the proposed definitions’ structure is presented. Keywords—Distributed systems, Grid programming models, Grid programming systems, Grid system definition. I.

We envision that many usage scenarios involving computational grids will be based on small, dynamic working groups for which the ability to establish transient collaboration with little or no intervention from resource administrators is a key requirement. Current grid security mechanisms support individual users who are members of well-defined virtual organizations. Recent research seeks to provide manageable grid security services for self-regulating, stable communities. Our prior work with component-based systems for grid computation demonstrated a need to support spontaneous, limited, short-lived collaborations. Such collaborations most often rely on shared or delegated fine grained access privileges to data and executable files as well as to grid compute resources. The mechanisms we are developing focus on the management and the enforcement of fine grained access rights. Our solution employs standard attribute certificates to bind rights to users (or their surrogates) and enables the high level management of such fine grained privileges which may be freely delegated, traded, and combined. Enforcement is provided by POSIX operating systems extensions that extend standard file permissions and regulate resource usage through access control lists. These extensions are available for common platforms and fully support legacy services.

One approach to application programming for the Grid is to implement services with often-used functionality on high-performance Grid hosts and provide them to the users located at clients. Complex applications are created by using several services and specifying the workflow between them. We discuss how the workflow of Grid applications can be described in an intuitive way as a High-Level Petri Net (HLPN), in order to orchestrate and execute distributed applications on the Grid automatically. Petri Nets provide an intuitive graphical workflow description, which is easier to use than script-based descriptions and is much more expressive than directed acyclic graphs (DAG). In addition, the workflow description can be analysed for certain properties such as deadlocks and liveness, using standard algorithms for HLPNs. We propose a platform-independent, XML-based language, called Grid Workflow Description Language (GWorkflowDL), and show how it can be adapted to particular Grid platforms. As two example target platforms, we discuss Java/RMI and the current WSRF standard. 1

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In the Grid computing community, there are several approaches to execute not only single tasks on single Grid resources but also to support workflow schemes that enable the composition and execution of complex Grid applications. The most commonly used workflow model for this purpose is the Directed Acyclic Graph (DAG). Within the establishment of the Fraunhofer Resource Grid, we developed a Grid Job Definition Language (GJobDL) that is based on the concept of Petri nets instead of DAGs to support the graph-based definition of arbitrary workflows on an abstract level. During the workflow execution, the abstract workflow must be concretized in order to be mapped onto the real Grid environment. This requires dynamic completion of the workflow based on actual information. It may be necessary to introduce new tasks – such as data transfers, deployment of software, authorization request, and data retrievals. These tasks can be represented by sub Petri nets that replace parts of the existent Petri net during runtime of the Grid application. We also propose a concept for fault management of entire job workflows by explicitly modeling the fault management within the workflow model. This fault management can be user-defined or be realized automatically by introducing new tasks enabling fault management based on fault management templates. 1

An important goal of grid computing is to apply the rapidly expanding power of distributed computing resources to large-scale multidisciplinary scientific problem solving. Developing a usable computational grid for Virginia Tech is desirable from many perspectives. It leverages distinctive strengths of the university, can help meet the research computing needs of users with the highest demands, and will generate many challenging computer science research questions. By deploying a campus-wide grid and demonstrating its e#ectiveness for real applications, the Grid Computing Research Group hopes to gain valuable experience and contribute to the grid computing community. This report describes the needs and advantages which characterize the Virginia Tech context with respect to grid computing, and summarizes several current research projects which will meet those needs.