I'm not sure I would agree that a Nack of 1 says "I haven't got any
messages". It only says:
I haven't got message number 1.
Cheers,
Christopher Ferris
STSM, Emerging e-business Industry Architecture
email:
blog: http://webpages.charter.net/chrisfer/blog.html
phone: +1 508 377 9295
"Jorgen Thelin" <> wrote on 09/22/2005 10:09:56 AM:
> I?d like to propose an alternate resolution for issue 25.
>
> In the meeting yesterday, we discussed issue 25 and the group expressed
its opinion that they
> preferred a definite statement to be made in this boundary case of no
messages received yet.
>
> The remaining proposal being considered last night was to send ?Ack
0..0? for the case where no
> messages have been received.
>
> <wsrm:SequenceAcknowledgement
xmlns:wsrm="http://docs.oasis-open.org/whatever">
> <wsrm:Identifier>http://example.org/mysequence/1234</wsrm:Identifier>
> <wsrm:AcknowledgementRange Upper="0" Lower="0">
> </wsrm:SequenceAcknowledgement>
>
> My intellectual concerns with this approach are that we are making an
incorrect statement ? we are
> acknowledging receipt of a message [#0] that (a) we haven?t actually
received, (b) doesn?t
> actually exist, and (c) will never be sent
>
> My practical concerns with this approach are that I fear this change may
cause a large ripple
> effect on implementations.
> I suspect implementations will need to change to explicitly recognize
and exclude / ignore the
> dummy message #0 anywhere they use a sequence range (although I haven?t
actually checked into the
> details yet).
> Also changing the schema to say #0 is in the message number range makes
it harder to do effective
> validation of message content on the wire (should you wish to do that) ?
specifically is Ack 0..10
> valid or just Ack 0..0?
>
> I believe we already have existing features of the RM spec that can be
used to solve this problem
> and make a definite but correct statement to handle this boundary
condition ? We can assert ?I?m
> still waiting for you to send me the first message? ? eg. ?Nack 1?
>
> <wsrm:SequenceAcknowledgement
xmlns:wsrm="http://docs.oasis-open.org/whatever">
> <wsrm:Identifier>http://example.org/mysequence/1234</wsrm:Identifier>
> <wsrm:Nack>1</wsrm:Nack>
> </wsrm:SequenceAcknowledgement>
>
> The advantages of this approach are:
>
> 1. It makes a definite statement rather than relying on the absence of a
statement to convey meaning
> 2. The statement made is accurate ? ?I haven?t received message #1?
> 3. We don?t need to change the message number range to accommodate this
boundary condition ? the
> schema can show the real 1..unbounded condition to allow better
validation of on-the-wire messages
> 4. We don?t need to introduce and document the concept of the fictitious
?Message #0? and explain
> where and when it is valid to use that message number
> 5. I _suspect_ the impact on existing implementation will be less by not
introducing lots of
> special-case handling code
> 6. We are re-using existing functionality in the spec rather than
introducing new functionality to
> handle special cases ? which should ultimately lead to fewer code paths
and a smaller surface area.
> 7. This approach is basically backward compatible with exiting spec
versions (both syntactically
> and semantically) ? it represents a clarification for this boundary case
rather than introducing
> completely new functionality.
>
>
> So I propose the following resolution for Issue 25
> Recommend that an RMD be required to respond with a
SequenceAcknowledgement element containing a
> Nack child element with content ?1? to signify that the first message
has not yet been received
> for a given Sequence. e.g.
> <wsrm:SequenceAcknowledgement
xmlns:wsrm="http://docs.oasis-open.org/whatever">
> <wsrm:Identifier>http://example.org/mysequence/1234</wsrm:Identifier>
> <wsrm:Nack>1</wsrm:Nack>
> </wsrm:SequenceAcknowledgement>
>
