RE: [ws-caf] Fault message formats

["Jim Webber" <Jim.Webber@newcastle.ac.uk>]

Hi Bryan:

[snip]

> <bpm>You have a good point that a message that reports on the state of
> an entity is different from a message that indicates that a previous
> message was not understood or valid. However, WS-Context defines some
> messages that are sent to indicate that a previously received message
> could not be properly processed. For instance,
> validContextExpectedFault, unknownContextFault, and even generalFault
> seems to be used for this purpose in many cases. These 
> messages are not
> just reporting that an entity has found itself in a particular state,
> but to inform the sender of a previously received message 
> that something
> was missing from the message, or something specified by the message
> could not be found. These seem like real faults to me, and as such, I
> would relay these messages using the SOAP fault element.</bpm>

It's perhaps a minor point, but I perceive the production of a
validContextExpectedFault message to be a normal state for the issuing
actor to be in, not a fault. If this had been called
validContextExpectedMessage then maybe we wouldn't be engaged in this
thread?

> <bpm>Could you explain the failure recovery characteristics you are
> trying to achieve - I don't remember reading about them in the spec?

Sure: using aysnchronous exchanges of mesasges allows the sender of a
message to fail and recover without disturbing the behaviour of the
intended recipient.

> Also, just because you describe something as request-response does not
> mean it can't be implemented asynchronously. 

That's true, but you need to correlate the messages appropriately.

> I think if 
> something really
> is request-response it helps the reader to understand the relationship
> between the messages to actually document it as request-response.

I don't think that the WS-CAF protocols are necessarily
request-response. Certainly in my mind the protocol actors just send
one-another messages at various points during protocol execution
(according to the "state machine" captured in the text). If the spec
gives that impression I'd blame the original authors. Oh, no wait a
minute... :-)

> <bpm>Lets not discuss the merits for now. I should not have mentioned
> WS-BaseFaults unless there was some agreement about the use of SOAP
> Faults.</bpm>

I absolutely agree.

Jim
--
http://jim.webber.name