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RE: Debating on the usefulness of supporting .... - Clarifying "Stateful Web Service Instance"

From: Savas Parastatidis <Savas.Parastatidis@newcastle.ac.uk>
Date: Fri, 20 Jun 2003 09:43:39 +0100
Message-ID: <BC28A9E979C56C44BCBC2DED313A447001D756BA@bond.ncl.ac.uk>
To: "marco" <events@oxfordsociety.org>, <www-ws@w3.org>

> 
> I use the term "Stateful Web Service Instance" with a meaning
compatible
> with the following:
> "Grid services can maintain internal state for the lifetime of the
> service. The existence of state distinguishes one instance of a
service
> from another that provides the same interface. We use the term Grid
> service instance to refer to a particular instantiation of a Grid
> service. " [6.1 The OGSA Service Model ]
> In this meaning, the relation between a web service and its stateful
> service instances vaguely resemble the one of a class and its objects.
> If Stateful Service Instances are supported, issues such as lifetime
> management and remote instance references must
> be taken into account.
> In this meaning, "Stateful Web Service Instance" are neither pervasive
> nor standard.
> 

As I said in my previous message, the semantics of the Grid Service
Instances (from OGSI) in relation to state and lifetime management can
be achieved in Web services without introducing O-O concepts, like class
and objects.

It is possible to associate state with context exchange. Upon retrieving
the context information, a Web service is capable of reasoning about the
state in relation to that context. Lifetime management related
attributes can be associated with the context (e.g., expiration time).

The difference between this approach and OGSI is that in Grid Service
Instances the semantics associated with statefulness are captured by the
Grid Service Handle that identifies that instance. You have to resolve
the GSH in order to get one or more Grid Service References (which is
very close to a context).

On the other hand, using a context-based approach (like the one used in
BTP and WS-Coordination) the state semantics are no longer associated
with a particular "instantiation" of a web service but, rather, with the
context.

Regards,
.savas.
Received on Friday, 20 June 2003 04:43:48 GMT

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