High Level Requirement Specification

Allow the use of Stateful Webservices - WSRF

Overview

Some services require the need to be stateful, and fulfill this by using the WSRF standard, rather than WSDL. Taverna needs to be able to query and invoke these types of services.

The WSRF is an evolution of the Open Grid Services Infrastucture (OGSI) version 1.0 specification, and is part of the Globus Toolkit.

"Web services must often provide their users with the ability to access and manipulate state, i.e., data values that persist across, and evolve as a result of, Web service interactions. And while Web services successfully implement applications that manage state today, we need to define conventions for managing state so that applications discover, inspect, and interact with stateful resources in standard and interoperable ways. The WS-Resource Framework defines these conventions and does so within the context of established Web services standards." - (WSRF Motivation)

"The WS-Resource Framework (WSRF) is a set of six Web services specifications that define what is termed the WS-Resource approach to modeling and managing state in a Web services context. To date, drafts of three of these specifications have been released, along with an architecture document that motivates and describes the WS-Resource approach to modeling stateful resources with Web services. To be released soon are the other specifications, an overview document describing the relationship among the different specifications, and a document that compares the WS-Resource Framework with the Open Grid Services Infrastructure."

The WSRF includes the following 6 specifications:

• WS-ResourceLifetime defines mechanisms for WS-Resource destruction, including message exchanges that allow a requestor to destroy a resource, either immediately or by using a time-based scheduled resource termination mechanism.
• WS-ResourceProperties defines how the type definition of a WS-Resource can be associated with the interface description of a Web service, and message exchanges for retrieving, changing, and deleting WS-Resource properties.
• WS-Notification defines mechanisms for event subscription and notification using a topic-based publish/subscribe pattern.
• WS-RenewableReferences defines a conventional decoration of a WS-Addressing endpoint reference with policy information needed to retrieve an updated version of an endpoint reference when it becomes invalid.
• WS-ServiceGroup defines an interface to heterogeneous by-reference collections of Web services.
• WS-BaseFaults defines a base fault XML type for use when returning faults in a Web services message exchange.

It is worth noting that whilst the WSRF specification is comprehensive, it is still a draft proposal and is being submitted to a standards body for final review in the near future before becoming offically standardized. However, it is not expected that the final specification will drastically differ from the draft.

Overall Goals

Implementation of WSRF into a fully functioning Taverna processor that fully supports the WSRF specification. The Globus Toolkit API provides support for WSRF based webservices.

Assessment

Affected Components

Taverna workbench. Scufl Model

Key Tasks

• Investigate and Understand the WSRF specification.
• Create a new Processor, and supporting classes, to handle WSRF
• Update UI to support the new processor type.

Appendix

WSRF Information Apache WSRF (Apache license)