Hey all,
Since Mark asked for my comment...
[...]
> I'm still waiting to see what the real differentiator is in the useage
> pattern, the interaction pattern, or whatever that means that this
> couldn't
> have been achieved with WS-RF. If you look at the paper that Savas et
al.
> produced many months ago, doesn't that map to precisely the same
goals,
> but
> using WS-Context at the core? Hopefully Savas can comment on this too.
>
[...] (lots of [...])
Mark, I agree with your arguments (I know... that doesn't happen very
often :-)
In our paper all those months ago we wanted to present a way to do
stateful interactions in a service-oriented fashion. WS-Context provided
us with the means to do just that. We wanted to model stateful
_interactions_ through message correlation.
There are many ways for doing this:
- BPEL uses properties from application messages to model stateful
interactions.
- One could use information in the messages to explicitly correlate
messages (e.g., order numbers explicitly sent as "arguments" to
operations) (similar to the above really).
- One could overload the semantics of a service and introduce "service
instances" (the OGSI approach and we know how that ended).
- Or, contextualisation could be used. WS-Context was the only
specification at the time explicitly talking about contextualisation
(and still the only one as far as I know).
Your choice of any of the above methods is application-specific. If you
want to model stateful interactions with a particular resource, you
could do it with any of the above ways. The WS-RF authors decided to use
WS-Addressing, which is fine. It means that parts of a WS-Address
structure will have to travel as headers in a message. It's a form of
contextualisation. However, it's not different from WS-Context which
scales better to multiple participant interactions. I can't see how this
could be done with WS-Resources.
Could WS-RF have used WS-Context? Sure! No doubt about that.
I would welcome an effort by the two communities to bridge their
differences. Until then... let's build some applications to test the
ideas: http://www.neresc.ac.uk/ws-gaf/AboutWSGAFApplication.html.
Best regards,
.savas.
