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RE: Web Service Description and stateful services

From: Savas Parastatidis <Savas.Parastatidis@newcastle.ac.uk>
Date: Tue, 20 May 2003 15:15:25 +0100
Message-ID: <BC28A9E979C56C44BCBC2DED313A447001C0C0DF@bond.ncl.ac.uk>
To: "Cutler, Roger (RogerCutler)" <RogerCutler@chevrontexaco.com>
Cc: <www-ws-arch@w3.org>

Here's a (very) brief description...

The Open Grid Services Architecture (OGSA) specifies the services that
an OGSA-compliant platform should support. The specifications of those
services are defined by various GGF working groups (work still in
progress). However, all the services MUST adhere to the Open Grid
Services Infrastructure (OGSI) specification.

OGSI defines the notion of a Grid Service Instance, which is a stateful
web service with lifetime related characteristics. A factory pattern is
employed to create service instances.

There is a Grid Service Description document which defines the interface
of Grid Service Instances and it is written in WSDL, with two
non-conformant extensions:

1. portType inheritance ("portType" has been renamed to "interface" in
WSDL 1.2 and the "extends" attribute has been included). This is not a
problem when we move to WSDL 1.2.

2. Service Data Elements (SDE)

SDEs are used to declare JavaBeans-like properties to services or
C++/Java like class/instance data members.

The "serviceData" element can appear in a portType and defines the
structure of exposed state. It has most of the attributes of xsd:element
with some additions. The way that "serviceData" is included in the WSDL
does not conform to WSDL 1.1 or 1.2. Furthermore, the way the
"serviceData" element has been defined does not conform to the
XML-Schema. I have already submitted a proposal that, if accepted, will
at least solve the non-conformance issues. 

Effectively it is a way to declare properties for services. The spec
does not associate these properties with messages. Instead, specific
operations are made available from the GridService portType (the one
that all Grid Service Instances must inherit) that allow get/set access
to the SDEs by using their names as arguments.

Although SDEs can be declared as part of a portType, the spec allows the
introduction of new SDEs at runtime. "Introspection" operations are
defined in the GridService portType. Also, consumers can subscribe to
SDEs to receive notifications.

The OGSI working group would like to see SDEs as part of WSDL.

I hope the above give a flavour.

I believe that the entire OGSI architecture is too object-oriented for
my liking. I have many issues with the approach, as I suggested in a
previous message, that I will bring to the OGSI working group. This
mailing list is not the place.

Dr. Savas Parastatidis 
Chief Software Architect, North-East Regional e-Science Centre 
School of Computing Science, University of Newcastle upon Tyne, UK 

> -----Original Message-----
> From: Cutler, Roger (RogerCutler)
> Sent: Tuesday, May 20, 2003 2:51 PM
> To: David Orchard; Christopher B Ferris; Savas Parastatidis
> Cc: www-ws-arch@w3.org
> I'd still like to hear specifically what these people are doing and,
> possible, what motivated them to put it in this place.
Received on Tuesday, 20 May 2003 10:15:33 UTC

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