RE: [Bug 8286] New: description of Subscription End ambiguous

Li,
  I tend to agree.  I think there's always an implicit exception with any 
MUST in the specs because if the system crashes and doesn't recover its 
entire state then clearly the MUST will probably not happen.  So I 
interpret these things as "if you're still up and running then you 
MUST...".  The reason I was ok with calling out this one case is because 
this message/situation is specifically for the case where something really 
bad happened.  But, I can go with your proposal to go with the MUST w/o 
the "unless..." part - it seems less confusing.

thanks
-Doug
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"Li, Li (Li)" <lli5@avaya.com> 
Sent by: public-ws-resource-access-request@w3.org
01/12/2010 10:43 AM

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<public-ws-resource-access@w3.org>
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Subject
RE: [Bug 8286] New: description of Subscription End ambiguous






Eventing Current text:
If the event source terminates a subscription unexpectedly, a
SubscriptionEnd SOAP message SHOULD be sent to the endpoint reference
indicated when the subscription was created (see 4.1 Subscribe). This
endpoint reference MUST refer to an endpoint that supports the
SubscriptionEndPortType portType.

Proposal:
If the event source terminates a subscription unexpectedly and the
wse:EndTo EPR was present in the Subscribe message for that subscription
(see 4.1 Subscribe), the SubscriptionEnd message MUST be sent to the
endpoint referenced by that EPR unless the event source is incapable of
transmitting any messages at all. 

I understand that the proposed change is to narrow the scope of
exception to the requirement. However, I also feel that MUST + exception
= SHOULD. 

I think MUST always means "absolute requirement" which may not be
achieved by a conformant implementation due to unforeseen situations. 

If we adopt the proposal, should we also check exceptions to all MUST?
For example, the (unless .... incapable ...) seems applicable to the
following requirement in WS-E 4.1 as well:

[Body]/wse:Subscribe/wse:Delivery/wse:NotifyTo 
This is an OPTIONAL element. When present, this element indicates that
notifications MUST be sent to the EndpointReference identified by this
element. 

I think it's better to just say MUST without any exception, or use
SHOULD, but not the mixed.

Thanks.

Li