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RE: Protocol independence

From: Mark Baker <mbaker@idokorro.com>
Date: Fri, 4 Apr 2003 12:27:17 -0500
Message-ID: <0503561D34C63045B07F04E5B3B2BFDC152368@FRED.planetfred.internal>
To: "Geoff Arnold" <Geoff.Arnold@Sun.COM>, <www-ws@w3.org>

Geoff,

> When I think of message transport independence in the context of WSA,
> I'm concerned about what happens when we move from HTTP
> to BXXP to SMTP to WAP-compressed-XML-over-GSSM/USSD
> to MOM. All of these support the transmission of XML messages
> and are (presumably) compatible with SOAP 1.2 and WSDL 1.x.
> However they have quite different performance and reliability
> characteristics. Further, some of them offer interesting
> features which are not available with others.

That's true, but you're forgetting the most important difference;
not all of those protocols are transport protocols.  For example,
BEEP has no method for "get me data", while HTTP does.  You can't
expect that bits sent with one can have the same meaning when sent
with the other; bits sent with BEEP necessarily has to include a
method, whereas bits sent with HTTP does not.

> How should
> a WSA address this diversity? Should we adopt a "lowest common
> denominator" approach, ignoring added value features? This seems
> likely to be unpopular, to put it mildly. Should we focus on
> abstractions which can be realized in different ways over
> different transports, in some cases using "native" features of the
> transport and in others using mechanisms layered on top of the
> transport? If so, who gets to define the mechanisms?

I think the "property" approach that SOAP 1.2 has taken is a decent
way forward here, so long as it is recognized that - at least when
dealing with application protocols - sometimes you shouldn't send a
message using a particular application protocol.  For example, SMTP
should not be used to retrieve things.

> Note that all of this falls strictly in the conventional SOA realm;
> I'm not venturing into esoterica such as the relationships between
> SOA and tuplespaces. We should not let red herrings distract us
> from ordinary everyday trout.

Sigh.  I thought it was a fine example of describing what an
application protocol was, and what "protocol independence" meant
to a TBS.  It is NOT a red herring, because the Web is very
similar to a TBS (just more general by focusing on everything
with identity rather than just on those things which can reasonably
be modelled as containers/spaces).

> Let me propose that at this stage all WSAWG should do is to
> create a glossary entry for "message transport independence".
> It needs to be sufficiently detailed to indicate that we're
> aware of the complexity and importance of the issue.

Sounds good.  It's easier to attack when it's written down.

MB
Received on Friday, 4 April 2003 12:27:18 GMT

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