Report on Schema Development relevant to UWS/CEA and Applications

Introduction

The Universal Worker Service (UWS) definition may be split into two parts

1. The mechanics of calling the service asynchronously - which are covered by the SOAP WSDL at the basic level with WS-Resource and WS-Notification standards layered on top as usage patterns. This half of the UWS specification is thus a "profile" of how to use these standards in a consistent fashion.
2. The description of the application or service. This is both a description of what a particular service does and how to call it. Ideally this description language can be standardized also and published in a registry to make it easier to connect the execution of different applications in a workflow and to make it easier to standardized GUIs.

AstroGrid has a prototype that covers both these aspects, though in a proprietary fashion, called the Common Execution Architecture (CEA). The intention is to evolve CEA appplication descriptions to become the UWS standard for application description.

Although the UWS work in general is part of the IVOA Grid and Web Services WG, the schema development has been a task of the "tiger team" of the Registry WG. This page reports on the current status of those efforts.

Application Description

In addition to the CEA description of an application (which would generally be invoked behind a web service), at the last IVOA interoperability meeting it was felt that there should be a generalised application description that could be used to describe any application with VO functionality that might be downloaded to a user's desktop.

The UML model of how the new Application type fits into the registry schema is presented below

Some features of this model;

• General metadata about an application - e.g. Source code language.
• Information about what VOStandards and data formats the application supports;
• Concepts of
  • Desktop application - with URIs to support automatic download and launching where possible
  • Software library.
  • CEA application.
• Can easily be extended to incorporate the registration of applications with new facilities - e.g. Plastic

In addition for the UWS specification of a remotely invocable application the CEA model (with some enhancements) will be adopted. The UML for this model is presented below.

• CEA Application:
  

The expression of this model as XML schema is work in progress.

Capability Reworking

To make the registration of services more flexible a refactoring of the Capability element has been proposed, which is essentially moving the Interface element within the Capability element and allowing a Service to have multiple Capabilities. This is represented by the following UML diagram for SIA.

• capability refactoring:
  

So, for instance, "SIA" is no longer a defining characteristic for a service but rather an attribute that it has (along with, say, VOStore capability)

The new scheme will support;

• Versioning of standards (e.g. specification of SIA 1.1 versus SIA 1.0 support)
• Support for multiple and "non-standard" interfaces per service.
• capability-specific information

-- PaulHarrison - 24 Feb 2006