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   Re: [xml-dev] lots of WS reading material

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Clay Shirky wrote:
> > "With Web Services, if you can read SOAP you can write SOAP. If you can
> > write SOAP you can read SOAP. So modulo only the firewall issue,
> > everybody's a peer."
> >
> > I don't understand that statement at all.
> Modulo the firewall issue was a math joke, and obviously a failed one,
> meaning "Excepting the leftover parts of the problem that come from
> the firewall issue."

I know what modulo means. But the "leftover part" is typically the part
which is less significant. i.e. "that project is done modulo a weekend's

It's a good joke, I guess, if it was intended like: "So the US is ready
to arrest Osama Bin Laden, modulo the small detail of actually finding
him." i.e. if you expected the audience to know that you were deferring
the hardest part of the problem.

> So yes, I absolutely agree that the firewall issues are significant. I
> was trying to say that SOAP mitigates other, non-firewall problems.

I would say that SOAP mitigates other, non-problems.

> Because both sides of a SOAP conversation have to read _and_ write
> SOAP, in the Web Service scenario, you avoid this assymetry.

That is not true. "SOAP messages are fundamentally one-way transmissions
from a SOAP sender to a SOAP receiver; however, SOAP messages are often
combined to implement patterns such as request/response."

In practice, SOAP "clients" tend to be able to read SOAP messages in
order to read return value. This does not change the fact that they are
*clients* and thus fundamentally assymetrical. This is easily
demonstrated using any SOAP toolkit for a statically typed language. You
generate a proxy for either a client OR a server. 

Of course it is trivial to generate both and build them into the same
program but that has always been true for HTTP also! The code to parse
an HTTP request and response is nearly the same. After the first line it
is a simple MIME message!

But if the clients and servers do not have a command line SMTP's "TURN"
command then you can't switch roles so you are no better off than with a
stricly unidirectional protocol. In SOAP you need to negotiate your own
"TURN"-ing protocol, just as you do in HTTP. 

 Paul Prescod


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