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RE: proposal for 7478

From: Martin Chapman <martin.chapman@oracle.com>
Date: Thu, 17 Sep 2009 19:12:24 +0100
To: "'Doug Davis'" <dug@us.ibm.com>, "'Li, Li \(Li\)'" <lli5@avaya.com>
Cc: <public-ws-resource-access@w3.org>, <public-ws-resource-access-request@w3.org>
Message-ID: <019101ca37c2$6aafa700$400ef500$@chapman@oracle.com>
I do find it a bit strange that expires is a minimum, as usually a "timeout" is a maximum.

The cleanest way to do this is to have a min and a max duration (both optional) and define the permutations.




From: public-ws-resource-access-request@w3.org [mailto:public-ws-resource-access-request@w3.org] On Behalf Of Doug Davis
Sent: 17 September 2009 15:15
To: Li, Li (Li)
Cc: public-ws-resource-access@w3.org; public-ws-resource-access-request@w3.org
Subject: RE: proposal for 7478


I think the current spec is pretty clear that there are two ways a subscription can end.  One is due to hitting the expires time and
the other is due to "some other reason".  No one, I think, will dispute that "some other reason" will always be possible. However,
the expires time is all about the normal termination of a subscription and that needs to be very well understood and agreed to.
Think of it this way, a normal expires will NOT generate a SubscriptionEnd message, while "some other reason" will (assuming an
EndTo is provided).  The expires time negotiation is all about the times when the SubscriptionEnd message is not involved.  These
two situations are not the same as you are implying - they have very different behavior - and (Gil should like this) the state
tables should show this difference.  :-) 

STSM |  Standards Architect  |  IBM Software Group
(919) 254-6905  |  IBM 444-6905  |  dug@us.ibm.com
The more I'm around some people, the more I like my dog. 

"Li, Li (Li)" <lli5@avaya.com> 

09/17/2009 10:06 AM 


Doug Davis/Raleigh/IBM@IBMUS 


<public-ws-resource-access@w3.org>, <public-ws-resource-access-request@w3.org> 


RE: proposal for 7478



I will focus on my response only to your part 2) as my previous email did. 
What concerns me is the semantics of "minimum" expiry time. If a subscriber asks for an expiry time 1 hour and tags it as minimum,
can the event source terminate the subscription before 1 hour? According to current spec, it can. And this is correct, because no
event source can predict the future and guarantee that the subscription will last for 1 hour. Therefore, a subscription with a
minimum 1 hour expiry is the same as a subscription with a "random" 1 hour expiry (one created without the minimum tag). Since there
is no difference in actual lifetime between two subscriptions, adding such a tag has no consequence but creates confusions for the


Li Li   



From: Doug Davis [mailto:dug@us.ibm.com] 
Sent: Wednesday, September 16, 2009 11:52 AM
To: Li, Li (Li)
Cc: public-ws-resource-access@w3.org; public-ws-resource-access-request@w3.org
Subject: Re: proposal for 7478 

Li wrote: 
> By change 1), it assumes all subscribers will never accept any
> subscriptions with a shorter expiration. Therefore, there is no need to
> create such subscription in the first place. While this may be the case
> in some situations, I'm not sure WS-E should enforce this assumption for
> all situations. In some situations, a subscriber may want to accept a
> subscription with a shorter expiration, with the hope that it can renew
> it later on when the event source is less loaded. 

this "hope" part is what worries me. W/o a clear guarantee that the subscription 
can be renewed then the subscriber is taking a large gamble.  It seems to me that 
in order to ensure we have a properly interoperable spec we need to be very 
clear about what both sides expect and want.  Gil's proposal does this but 
you are correct that it assumes the subscriber only cares about the minimum duration. 
You point out that a subscriber might really be ok with the uncertainty 
around being able to renew (the 'hope' part) - but if so then it needs to 
tell the source this bit of information. 

To me there are two parts of this: 
1 - we need to make sure that the source advertises what it supports by 
using policy.  This means that if we keep duration and dateTime then there is 
no interop problem as long as the source tells people which it supports. 

2 - we need to make sure that the subscriber tells the source what it 
expects w.r.t. the new subscription.  This means that when it asks for an 
expires time it needs to not only tell it the duration/dateTime, but it 
should also indicate whether this is an upper limit or a lower limit, or 
even just a suggestion.  Perhaps a new attribute on the Expires element to 
indicate this would do it.  W/o this flag I don't think we can get the 
level of interop we want by sticking with the current "random" expires time 

Received on Thursday, 17 September 2009 18:13:22 UTC

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