RE: [wsrf] Singleton Resource Pattern - meaning of "implied"

["Savas Parastatidis" <Savas.Parastatidis@newcastle.ac.uk>]

Hey Tim,

Thanks for this. 

I don't think this clarifies things. What does it mean to have
"implicit" or "explicit" execution context. If you include something in
a message, either in the header or in the body, you are doing so
explicitly. If the middleware does it for you without your knowledge,
that's a different manner. The case still remains that the service
requires you to include something in the message that is going to be
used for its own purposes. This is not bad per se. What's bad, in my
opinion, is that as a requestor you have to reason about it, you have to
be aware of what you are talking to (i.e., the resource). At the
architecture level, you are sending messages to the resource and not to
the service (the service just happens to receive the messages on the
resource's behalf). There is nothing implicit about this.

I would have called it an "implicit" pattern if I didn't have to do
absolutely anything special as a requestor and the service was able to
figure out things just from the message I send. For example, I send a
document that requests a status report on a previously submitted order.
As we do in real life, I give the order number as part of my request. I
talk to the service. The service will analyse the document and figure
out what information it needs from the entire document (e.g., the order
number plus my name) to establish the execution context. We do this
today already and it's called service-orientation. BPEL is based on the
same idea. We don't need to _explicitly_ model resources. (But I think I
am going to a different argument here :-)

Best regards,
--
Savas Parastatidis
http://savas.parastatidis.name
 

> -----Original Message-----
> From: Tim Banks [mailto:tim_banks@uk.ibm.com]
> Sent: Monday, July 12, 2004 6:32 PM
> To: Savas Parastatidis
> Cc: wsrf@lists.oasis-open.org
> Subject: RE: [wsrf] Singleton Resource Pattern - meaning of "implied"
> 
> 
> 
> 
> 
> Savas,
> 
> The rationale for the 'implied' term is in the "Modelling Stateful
> Resources with Web Service" paper (see
>
http://www.oasis-open.org/apps/org/workgroup/wsrf/download.php/6795/ws-
> modelingresources.pdf
>  )
> 
> "The term implied is used because the stateful resource associated
with a
> given message exchange is treated as implicit execution context for
the
> message request. By implicit, we mean to say that the requestor does
not
> provide the identity of the resource as an explicit parameter in the
body
> of the request message. Instead, the context used to designate the
implied
> stateful resource is encapsulated in the WS-Addressing endpoint
reference
> used to address the target Web service at its endpoint."
> 
> Regards, Tim Banks
> IBM TP Architecture & Technology. Hursley, UK.
> Phone: External +44 1962 815639, Internal 245639
> 
> "Savas Parastatidis" <Savas.Parastatidis@newcastle.ac.uk> wrote on
> 12/07/2004 17:00:02:
> 
> > Hey Steve,
> >
> > Please excuse my non-understanding of the terms that you use but I
> > wonder why "implied" is used. There is nothing implied about the
> > existence of a resource and the fact that it becomes the logical
> > recipient of the messages.
> 
> <snip>