Workflows form the essential part of the process execution both in a single machine and in distributed environments. Although providing conditional structures is not mandatory for a workflow management system, support for conditional workflows is very important in terms of error handling, flexibility and robustness. Several of the existing workflow management systems already support conditional structures via use of different constructs. In this paper, we study the most widely used workflow management systems and their support for conditional structures such as if, switch, and while. We compare implementation of common conditional structures using each of these workflow management systems via case studies, and discuss capabilities of each system.

Emir M. Bahsi

Emrah Ceyhan

Tevfik Kosar

Conditional Workflow Management: A Survey and Analysis

This paper discusses issues in the distribution of bundled workflows across ubiquitous peer-to-peer networks for the application of music information retrieval. The underlying motivation for this work is provided by the DART project, which aims to develop a novel music recommendation system by gathering statistical data using collaborative filtering techniques and the analysis of the audio itsel, in order to create a reliable and comprehensive database of the music that people own and which they listen to. To achieve this, the DART scientists creating the algorithms need the ability to distribute the Triana workflows they create, representing the analysis to be performed, across the network on a regular basis (perhaps even daily) in order to update the network as a whole with new workflows to be executed for the analysis. DART uses a similar approach to BOINC but differs in that the workers receive input data in the form of a bundled Triana workflow, which is executed in order to process any MP3 files that they own on their machine. Once analysed, the results are returned to DART's distributed database that collects and aggregates the resulting information. DART employs the use of package repositories to decentralise the distribution of such workflow bundles and this approach is validated in this paper through simulations that show that suitable scalability is maintained through the system as the number of participants increases. The results clearly illustrate the effectiveness of the approach.

Eddie Al-Shakarchi

Pasquale Cozza

Andrew Harrison

Carlo Mastroianni

Matthew Shields

Domenico Talia

Ian Taylor

Distributing Workflows over a Ubiquitous P2P Network

David Walker

Ewa Deelman

Dynamic Computational Workflows: Discovery, Optimisation and Scheduling

An approach to dynamic workflow management and optimisation using near-realtime performance data is presented. Strategies are discussed for choosing an optimal service (based on user-specified criteria) from several semantically equivalent Web services. Such an approach may involve finding &#x22;similar&#x22; services, by first pruning the set of discovered services based on service metadata, and subsequently selecting an optimal service based on performance data. The current implementation of the prototype workflow framework is described, and demonstrated with a simple workflow. Performance results are presented that show the performance benefits of dynamic service selection. A statistical analysis based on the first order statistic is used to investigate the likely improvement in service response time arising from dynamic service selection.

David W. Walker

Lican Huang

Omer F. Rana

Yan Huang

Dynamic Service Selection in Workflows Using Performance Data

In this paper we examine the issue of optimizing disk usage and scheduling large-scale scientific workflows onto distributed resources where the workflows are data-intensive, requiring large amounts of data storage, and the resources have limited storage resources. Our approach is two-fold: we minimize the amount of space a workflow requires during execution by removing data files at runtime when they are no longer needed and we demonstrate that workflows may have to be restructured to reduce the overall data footprint of the workflow. We show the results of our data management and workflow restructuring solutions using a Laser Interferometer Gravitational-Wave Observatory (LIGO) application and an astronomy application, Montage, running on a large-scale production grid-the Open Science Grid. We show that although reducing the data footprint of Montage by 48&#x25; can be achieved with dynamic data cleanup techniques, LIGO Scientific Collaboration workflows require additional restructuring to achieve a 56&#x25; reduction in data space usage. We also examine the cost of the workflow restructuring in terms of the application's runtime.

Gurmeet Singh

Karan Vahi

Arun Ramakrishnan

Gaurang Mehta

Henan Zhao

Rizos Sakellariou

Kent Blackburn

Duncan Brown

Stephen Fairhurst

David Meyers

G. Bruce Berriman

John Good

Daniel S. Katz

Optimizing Workflow Data Footprint

We describe techniques to support the runtime execution of scientific workflows in the ASKALON Grid environment. We present a formal model and three middleware services that support in combination the effective execution in heterogeneous and dynamic Grid environments: performance prediction, scheduling, and enactment engine. We validate our techniques with concrete experimental results for two real-world applications executed in the Austrian Grid environment.

Radu Prodan

Specification and Runtime Workflow Support in the ASKALON Grid Environment

The over-arching aim of Grid computing is to move computational resources from individual institutions where they can only be used for in-house work, to a more open vision of vast online ubiquitous `virtual computational' resources which support individuals and collaborative projects. A major step towards realizing this vision is the provision of instrumentation &#x2013; such as telescopes, accelerators or electrical power stations &#x2013; as Grid resources, and the tools to manage these resources online. The GRIDCC project attempts to satisfy these requirements by providing the following four co-dependent components; a flexible wrapper for publishing instruments as Grid resources; workflow support for the orchestration of multiple Grid resources in a timely manner; the machinery to make reservation agreements on Grid resources; and the facility to satisfy quality of service (QoS) requirements on elements within workflows. In this paper we detail the set of services developed as part of the GRIDCC project to provide the last three of these components. We provide a detailed architecture for these services along with experimental results from load testing experiments. These services are currently deployed as a test-bed at a number of institutions across Europe, and are poised to provide a 'virtual lab' to production level applications.

A. Stephen McGough

Asif Akram

Li Guo

Marko Krznaric

Luke Dickens

David Colling

Janusz Martyniak

Roger Powell

Paul Kyberd

Chenxi Huang

Constantinos Kotsokalis

Panayiotis Tsanakas

GRIDCC: A Real-Time Grid Workflow System with QoS

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Scientific Programming provides a forum for research results in, and practical experience with, software engineering environments, tools, languages, and models of computation aimed specifically at supporting scientific and engineering computing.

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Chief Editor&nbsp;Professor Tramontana&nbsp;is based at the University of Catania and his research primarily concerns the areas of software engineering and distributed systems.

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