Re: Proposed text on reliability in the web services architecture

Hao,

> I think Walden has made a good point. We don't really care about RM, which
> itself has been solved in the TCP/IP layer or other messaging layer
already.
> The whole RM thing is misleading within Web Services context. What we
really
> care is a reliable way of coordinating a client and its server, although
RM
> might be helpful.

Agreed.

>
> Making an operation idempotent seems to be a simple and effective
solution.

I'm leery of this.  If you mean making it idempotent by enclosing it
within a message and giving the message identity, then I'd say you were
doing RM.  If you mean recognizing that something like a deposit has
identity from the client's perspecitive, and allow the client to set the
value of the deposit directly, then fine.  I'd call it "finding", not
"making".

> What we need to distinguish
> is the difference between logical operations and physical operations.
>
> In the bank account example, depositing money into an account is a logical
> operation while sending
> a request to the bank's Web Services to achieve such an operation is
> physical. A logical operation can
> be idempotent or not, but we do want all physical operations to be
> idempotent.  More precisely, we mean:
> 1. r=f(u,x,t), where f is a physical operation on a Web Services
identified
> by u, x is a request, and t is time, and r is the results returned by the
> WS.
> 2. r'=f(u,x',t')
> 3. if x eq. x', and r eq. r', then we say that f is idempotent, where eq.
> stands for "is equivalent to".
> This idempotent def is different than the one in math.
>
> Is this summary good enough?

It's not clear enough.  When you say "sending a request", and having
that be idempotent, what is the thing that has identity?  If it's a message,
then the above summarizes RM.  If it's a "deposit", then the above
summarizes an application level coordination.

Thanks,

Walden