Re: WS-Eventing issue

Am 05.01.2011 12:17, schrieb Doug Davis:
> 
> public-ws-resource-access-request@w3.org wrote on 01/05/2011 04:48:51 AM:
>> Hi everybody,
> 
> Hi David,
> 

Hi Doug,

>> I'm new to this mailing list. I come from Germany, institute of
>> telematics at the University of Lübeck. I'm working with WS-Eventing and
>> got some problems while reading the specification. Recently I had talked
>> to Wu regarding to the missing wse:Identifier in the current working
>> draft (http://www.w3.org/TR/2010/WD-ws-eventing-20100805). Wu told me
>> that the wse:Identifier was removed because it is inconsistent with the
>> WS-Addressing principle that reference parameters should be opaque.
>> Instead of using wse:Identifier, the event source should provide an
>> unique subscription manager EPR for every event subscription.
> 
> Correct - each Subscription Manager EPR should be unique - if there
> is a need to know which one is being addressed.  There may be cases where
> one EPR (SubMgr) is all that's needed but I think those are pretty rare.
> 
>> First it would be useful if the foregoing information is emphasized
>> within the WS-Eventing specification. After reading the "2.4
>> Subscription Managers" section
>> (http://www.w3.org/TR/2010/WD-ws-eventing-20100805/#SubMgr) again,
>> together with Wu's background knowledge, the subscription manager
>> behaviour mentioned above would be clear. What's your opinion?
> 
> While I think the uniqueness aspect/requirement of the EPR is implied,
> it can't hurt to be a bit clearer about this in 2.4.
> 
>> The method above works very well with one exception (may be I've not
>> understand the reasonable cause behind the subscription end message): if
>> an event source wants to quit a subscription by using a subscription end
>> message, no subscription manager EPR is given to indicate the terminated
>> subscription. If you take a look at the 2006' WS-Eventing submission, a
>> subscription manager EPR is transmitted (comparing
>>
> http://www.w3.org/Submission/2006/SUBM-WS-Eventing-20060315/#Subscription_End
>> with
>> http://www.w3.org/TR/2010/WD-ws-eventing-20100805/#SubscriptionEnd).
>> What's the reason for this modification? Should a subscription end
>> message only be sent when every subscription is terminated? Otherwise,
>> wow does an event sink know which subscription is terminated?
> 
> The SubscriptionEnd message will be sent to the NotifyTo EPR of that
> subscription.
> This means that multiple SubscriptionEnd messages can be differentiated
> the same
> way multiple Notifications messages (from differing subscriptions) are
> differentiated.
> And this is done via the same mechanism that differentiates SubMgr EPRs.
>  In other words,
> when someone subscribes, and provides a NotifyTo EPR, they are expected to
> make it unique enough so that messages (notifications or SubEnd msgs)
> will be
> distinguishable from messages from other subscriptions.  This will
> typically mean
> they will include a unique ref-parameter.  Its worth noting that, just
> like in the
> SubMgr EPR case, if a subscriber doesn't care to make this distinction
> then they
> are not required to make each NotifyTo EPR unique - its up to them.
> 
> You are correct that ws-e used to include the SubMgr EPR in the SubEnd
> message but
> this was problematic because there was no well-defined EPR comparison
> algorithm
> defined.  So, w/o that there was no guaranteed way to check which SubEnd
> msg came
> from which subscription.  But, since each Notification msg might need to
> be linked
> to its subscription as well and we do that linking through unique
> NotifyTo EPRs
> it made sense to use the same mechanism for the SubEnd msg.
> 
> Does this help or make sense?
> 

Yes, this really helps a lot - and makes sense as long as there is no
subscription manager EPR comparing algorithm. Otherwise imho the logical
relation between a subscription manager EPR and a subscription end
message makes more sense than the relation between a subscription
manager EPR and the NotifyTo EPR. But at least I think it's a matter of
taste :-)

Until now I was not aware that NotifyTo EPRs are unique. I noticed them
within the subscription messages as a destination for notifications
without the uniqueness in mind. But this is mandatory for event sinks to
distinguish between different notification messages - ok, check. :-)

But now there is a little inconsistency regarding to the example
messages of the WS-Eventing spec. Please have a look at example 4-1
(http://www.w3.org/TR/2010/WD-ws-eventing-20100805/#Table4) and notice
the wsa:Address within wsa:ReplyTo and the wsa:Address within wse:NotifyTo.

ReplyTo: http://www.example.com/MyEvEntsink
NotifyTo: http://www.other.example.com/OnStormWarning

As you mentioned above, NotifyTo is a unique EPR to distinguish
notifications and subscription end messages. Now consider example 4-9
(subscription end,
http://www.w3.org/TR/2010/WD-ws-eventing-20100805/#Table12) and example
5-1 (notification,
http://www.w3.org/TR/2010/WD-ws-eventing-20100805/#Table13).

Example 4-9 is addressed to http://www.example.com/MyEventSink
Example 5-1 is addressed to http://www.other.example.com/OnStormWarning.

Shouldn't example 4-9 also addressed to
http://www.other.example.com/OnStormWarning to identify the correct
subscription?

I hope my posts are not redundant or too basic :-)

Best, David

> -Doug
> 
> 
>> Thanks in advance for your hints und helps,
>>

Received on Wednesday, 5 January 2011 12:12:59 UTC