John, (01)
you wrote: (02)
> Message passing is the most fundamental of all these methods.
> Subroutine call is one very constrained special case. The O-O
> paradigm is another special case.
>
> EB> With all due respect, I think the request/response interaction
> > paradigm is fundamental to "service-oriented". As discussed in
> > other venues, the actual technical interaction can be more complex
> > than request/response, but the fundamental paradigm cannot be.
>
> I agree, but I would say that "request/response" is another special
> case of message passing. ... (03)
We are on different wavelengths here. Message passing is a nominal
model for pretty much every variety of communication that is
recipient-specific, as distinct from "broadcast-like". (04)
I agree that request/response is a special case. The important idea is
that the request "message" is targeted to a specific "role" in the
system that is nominally played by a single correspondent, who may or
may not be known to the requestor. And the message is a request for a
service that the correspondent is expected to provide. And the response
is a message directed to the requestor that may include the provision of
the service, or just the notification that the service has occurred,
will occur or won't occur. (05)
> There are many kinds of message types that
> are neither requests nor responses, (06)
And their relationship to an SOA is undefined. (07)
> and not all requests trigger a
> response from the intended recipient. For example, a request sent
> to an executive might be read by a secretary, who forwards it to
> an assistant, who sends a response. (08)
But from an SOA point-of-view, the request goes to the _role_ -- from
outside, the "executive" denotes a person as the image of the "office"
-- and the participant that actually plays that role -- the "office" --
is the provider. The internal process of the office is encapsulated --
the requestor neither knows nor cares how that actually works. (09)
In the same way, Zoom Motors can issue a request for a metal part to a
"first-tier supplier" Metals-R-Us who functions as a broker and chooses
one of several small foundries to make those parts. From the
point-of-view of Zoom Motors, Metals-R-Us supplied the parts. (010)
-Ed (011)
--
Edward J. Barkmeyer Email: edbark@xxxxxxxx
National Institute of Standards & Technology
Manufacturing Systems Integration Division
100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
Gaithersburg, MD 20899-8263 FAX: +1 301-975-4694 (012)
"The opinions expressed above do not reflect consensus of NIST,
and have not been reviewed by any Government authority." (013)
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