Workshop on Web Services-based Grid Applications (WSGA)

Abstracts:

Keynote:
The Good, the Bad and the Ugly: The Web Services Stack, and the Myths of Interoperability, Jon MacLaren

There is much talk in the Grid and Web Services community about interoperability, and how vital it is. However, opinions differ on how this should be achieved, some favoring the universal adoption of emerging standards and platforms, while others take the view that only well-established, widely-deployed and adopted standards should be used. This talk looks at what these communities mean by interoperability, and argues that the focus of the discussion - which is usually on technology, rather than methodology - is mistaken.

A technology-neutral approach to building services is outlined that advocates and encourages a simple software stack. Here, the focus is on thinking about message exchange patterns, and thinking about how to behave when remote services fail, or become unavailable. We show, by example, that this approach leads to services that are easy to build clients for.

This talk makes heavy use of the distributed systems literature, much of which is 10-20 years old, but is very relevant.

A Comparative Study of Web Services-based Event Notification Specifications, Yi Huang and Dennis Gannon

Web services-based event notification is an emerging technology that combines the asynchronous communications feature of event notification mechanisms and the interoperability feature of Web services technologies. Web services-based event notification systems are important components for Services-Oriented Grid computing. WS-Eventing and WS-Notification are two major competing specifications on these systems. Previously, several other specifications were proposed in order to create interoperable event notification systems, including CORBA notification services, JMS and OGSI notification. What are the differences among these specifications? Do we really need two competing Web services-based event notification specifications? This paper is a comparative study on these Web services-based event notification specifications. The focuses are on identifying the similarities and differences between these two specifications and identifying their evolution path from previous specifications. We found that competing Web services specifications take merits from each other during the development progress, which is good for the maturity of Web services-based event notification technology. We also identified several major changes from previous event notification systems to Web services-based event notification systems. In the end, we will present our WS-Messenger project that supports both WS-Eventing and WS-Notification specifications and provides mediation between them.

A Hybrid XML-Relational Grid Metadata Catalog, Scott Jensen, Beth Plale, Sangmi Lee Pallickara, and Yiming Sun

The ability to manage metadata is a critical requirement of the grid, but scientists have not been given the tools needed to catalog experimental data based complex metadata attributes. Our research has shown that the specific characteristics of metadata catalogs require a different approach than that used for general queries over XML data. This paper presents a hybrid approach to storing XML in a relational database that exploits the specific characteristics of a metadata catalog.

A Mechanism for Creating Scientific Application Services On-demand from Workflows, Gopi Kandaswamy and Dennis Gannon

Service Oriented Computing is a new paradigm for accessing, integrating and coordinating loosely coupled software systems in a standardized way. It is increasingly being employed by large scientific collaborations to "wrap" applications as web services i.e. to create an additional "web services layer" on top of existing scientific applications. This enables scientists to easily compose, monitor and run complex workflows consisting of scientific applications that are not only developed and managed by a distributed team of application developers but also run on a distributed set of heterogeneous resources. However, one of the biggest challenges for large scientific collaborations lies in keeping all the web services persistent so that they can be accessed from scientific workflows whenever needed. In this paper we discuss the architecture and implementation of a mechanism by which we can create the web services on-demand, in the event that they are unavailable during the execution of a scientific workflow and thus obviate the need to keep them persistent.

TrustCell: Towards the End-to-End Trustworthiness in Data-Oriented Scientific Computing, Sangmi Lee Pallickara and Beth Plale

Data-driven computational science on community computational resources is frequently of a magnitude and scale that it requires that computations be done remotely, generating resulting data collections that are too large to be shipped back to a user's workstation. Service-oriented middleware is well equipped to carry out actions on behalf of a user, but SOA middleware does not address user trust in the privacy of their actions and security of their data. In this paper we first identify the role of trust in a large distributed computation then develop a model that represents the trust relationship between the users and their remote resources in the Grid system. We show how one can construct a trusted relationship from the model, with an emphasis on the importance of context to a specific trust relationship. We provide a case study of a data-driven scientific application that executed across multiple organizations.