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Re: WS-Eventing optionality analysis

From: David Snelling <David.Snelling@UK.Fujitsu.com>
Date: Tue, 5 Oct 2010 13:11:25 +0100
CC: "public-ws-resource-access@w3.org" <public-ws-resource-access@w3.org>
Message-ID: <95F567B7-CB88-42B7-8BE0-2FCA7E899A01@UK.Fujitsu.com>
To: Doug Davis <dug@us.ibm.com>
Folks,

I'm not sure where all this is going to end, but we at least need to remove the use of "indefinite":

From Wiki:
indefinite (comparative more indefinite, superlative most indefinite)
Without limit; forever, or until further notice; not definite.
Vague or unclear.
Undecided or uncertain.
(mathematics) An integral without specified limits.

From Oxford Concise:

indefinite - adj.
Not clearly expressed or defined; vague.
> lasting for an unknown or unstated length of time.

From Doug's Book of Spec Words:
indefinite - adj.
"dunno".



On 5 Oct 2010, at 02:03, Doug Davis wrote:

> 
> Gilbert Pilz <gilbert.pilz@oracle.com> wrote on 10/04/2010 07:06:25 PM:
> > I think that the problem with both the current spec and your 
> > comments below is that the way the terms "expire", "expiration" etc.
> > are used is conflating two separate concepts. One of them (which you
> > refer to as the "expiry feature") concerns the resource management 
> > strategy employed by the subscription manager to manage the 
> > resources associated with a subscription; the idea that every 
> > subscription will be automatically cleaned up a specific, known time
> > etc. The other concerns the existence (or lack thereof) of an agreement
> > between the subscriber and the subscription manager as to if/when 
> > the subscription will be automatically deleted. This conflation of 
> > these two ideas is causing problems.
> 
> Do you purposely say "automatically cleaned up" in one spot and 
> "automatically deleted" in another?  I'm just curious if they 
> mean the same thing or not.  To me they do so I'll assume they do 
> to you too. 
> 
> To me you can't separate these two as part of the protocol.  W/o the 
> "automatic cleanup" due to a timeout feature, you have no need for the 
> Expires element at all.  Said, another way, if Subscriptions were never 
> "automatically cleaned-up" due to time, and people had to call Unsubscribe, 
> there wouldn't be the need for this negotiation at all. 
> 
> > First, there is no reason for a subscriber to want or need to know 
> > anything about the resource management strategies used by the 
> > subscription manager. Any attempt to communicate this information 
> > represents a hole in our abstraction of a subscription manager - a 
> > hole that can only cause misunderstandings and interoperability 
> > problems. 
> 
> The only reason to not communicate this information is if it doesn't 
> matter.  But knowing when a Subscription will be "automatically 
> cleaned-up" could be vital to a subscriber otherwise they'll never 
> know when to call Renew.   
> 
> Your first sentence is very confusing to me.  If we accept the notion 
> that Expires in some form needs to remain (which I think everyone will 
> agree to), then how can a subscriber not want/need to know what the 
> resource management strategy is?  At least w.r.t. this notion of 
> "automatic cleanup" due to time.  That's really all Expires is about.   
> Remove the desire to explain _when_ this "automatic cleanup" will happen 
> and you remove the need for Expires.  Unless you don't consider 
> "automatic cleanup" due to tie to be part of the "resource management strategy". 
> (I discuss this "part of" notion a bit later on) 
> 
> > For an example, consider the disconnects around the use of
> > the phrase "indefinite" and the value "PT0S". Some people seem to 
> > think it means "never", others "a really, really long time" and 
> > others simply "you don't know". The idea of an "indefinite 
> > expiration" is both useless and dangerous.
> 
> Aside from some of our private IMs, I've never heard anyone refer to it 
> as "you don't know".  And "never" and "a really, really long time" are, for 
> our purposes, the same thing.  If there are words in the spec to imply 
> that PT0S/indefinite means "dunno" then we need to fix that because that 
> level of uncertainy is asking for an interop problem.  Can you show me 
> where in the spec "dunno" might be implied?  I find text like this: 
>   If this element does not appear, then the subscription will not 
>   expire. That is, the subscription has an indefinite lifetime. Likewise, 
>   a value of PT0S indicates that the subscription will not expire. 
> Which is pretty clear to me that its not "dunno". 
> 
> > Secondly, we have to keep in mind that there are many different ways
> > to manage the resources associated with a subscription. One strategy
> > could be to simply monitor the level of various critical resources 
> > and, when these reach a low water mark, start deleting subscriptions
> > on a least recently used basis. A subscription manager that 
> > implements this strategy can not tell you when, or even if, it is 
> > going to "expire" a subscription - whoever implemented it probably 
> > wasn't even thinking in those terms. It's simply not true to say 
> > that "all subscription managers implicitly support the notion of expiry".
> 
> This is mixing topics.  While a Subscription Manager may choose to 
> have this kind of resource management code, this is separate from the 
> "automatic cleanup" code that is tied to the Expires element.  And 
> it would be a mistake to call this kind of cleaning up "subscription 
> expiring" - at least per the current spec's use of the term.  Today, 
> the Expires element and the notion of "expiry" are all based on time. 
> Yes there may be other factors when determining when to "automatically 
> cleanup" a subscription, but those are out of scope of the spec and 
> the expiry feature (and therefore the Expires element). 
> 
> It seems to me that the real issue coming from this "low water mark" 
> type of example is whether or not it triggers the EndTo processing, 
> not how its related to Expires/expiry/timeout.  Think of it this way... 
> there are potentially many ways a Subscription could be deleted. 
> Unsubscribe and "expiry" are just two of them.  Each of these are 
> well defined in terms of what the protocol elements mean w.r.t. 
> this part of the resource mgmt code.  This doesn't mean there couldn't 
> be other aspects of the resource mgmt code - it just means we're not 
> touching on them in the spec.  Section 4 of the spec include this: 
>   In addition, the Event Source/Subscription Manager MAY cancel a 
>   subscription at any time, as necessary. 
> I think your "low water mark" example falls into that category. I 
> just don't know if it is considered "unexpectedly" and should 
> trigger the EndTo processing - or not.  Perhaps the spec needs to 
> clear that part up?  I'm leaning towards saying it should trigger 
> it since its deleting the Subscription for reasons that are not 
> covered by the spec, but if some extension defines it in such a way 
> as to make this trigger "expected" to a Subscriber then we're back 
> to not triggering EndTo. Sigh. 
> 
> > I think that, to be of any use at all, we need to narrow down the 
> > definition of "expiration" to refer to "the agreement between the 
> > subscriber and the subscription manager on when then subscription 
> > will be automatically terminated". 
> 
> To me it already means this and I'm still not clear on where in the 
> spec it implies anything else. 
> 
> > We might even want to change all 
> > occurrences of the English word "expiration" to "subscription 
> > expiration". This is analogous to the stock trading term "stock 
> > option". In English, the word "option" means very loosely "the 
> > right/ability to do something", but in context of equity trading a 
> > "stock option" refers to an explicit, legally binding agreement 
> > between two parties. We need the term "subscription expiration" to 
> > have the same flavor.
> > 
> > Finally, we need to reduce the number of ways that the WS-Eventing 
> > protocol signals the existence (or lack thereof) of subscription 
> > expiration agreement. 
> 
> I'm not following this.  The presence or absence of the Expires element 
> has no impact on whether there is an agreement around expiration. 
> Per the spec today, the absence of the Expires element implies PT0S. 
>   If this element is not present, the implied default expiration time 
>   is indefinite. A value of PT0S indicates a request for an indefinite 
>   expiration time. 
> This means that it has the same semantics as Expires+PT0S.  While this 
> does mean that there are two ways of saying the same thing, I don't 
> think this it introduces any confusion around the expiry feature. 
> We can remove the optionality of the Expires element if that helps, but 
> to me it was always just a handy short-hand notation. 
> 
> Likewise, we have similar text for GrantedExpires.  Its absence is 
> equivalent to its presence+PT0S. 
>   If this element does not appear, then the subscription will not 
>   expire. That is, the subscription has an indefinite lifetime. Likewise, 
>   a value of PT0S indicates that the subscription will not expire. 
> 
> It may be confusing to some people that the text we use in each of 
> these cases is slightly different: 
>   will not expire 
>   indefinite lifetime 
>   indefinite expiration time 
>   expiration time is indefinite 
> and we can be more consistent if that helps. 
> 
> > I think the following should apply:
> > 
> > 1. If the subscriber has no interest in whether/if the subscription 
> > will be automatically deleted, it does not include the Expires 
> > element in the Subscribe request. In such cases the subscription 
> > manager MUST NOT include the GrantedExpires element in the 
> > SubscribeResponse. The end result will always be that there is no 
> > subscription expiration. If EndTo was specified, the subscription 
> > manager MUST send a SubscriptionEnd message if/when it automatically
> > deletes the message since there was no way for the subscriber to 
> > know if/when this was going to happen.
> 
> I'm not in favor of introducing the notion of a subscriber having 
> "no interest in whether/if the subscription will be automatically 
> deleted".  Back in our MEX discussions we argued to remove the "whateva" 
> dialect - I'm not in favor of adding a "whateva" Expires time in 
> WS-Eventing. :-)   In this case, as silly as it may sound, someone 
> can choose to make all "whateva" subscriptions exactly 1 second long 
> and be spec compliant.  I have no idea what Subscriber would ever 
> actually ask for this kind of randomness.  As you say later on, 
> if they really don't have a preferred timeout then they can use
> @BestEffort with some Expires time. 
> 
> > 2. If the subscriber needs to know whether/if the subscription will 
> > be automatically deleted, but doesn't wish to "bid" a particular 
> > time, it includes the Expires element with a value of "PT0S". If the
> > subscription manager knows or can figure out if/when the 
> > subscription will be automatically deleted, and it wishes to share 
> > this information with the subscriber (i.e. it supports the 
> > negotiation of a subscription expiration), it accepts the request 
> > and indicates that time via the GrantedExpires element in the 
> > SubscribeResponse. 
> 
> Now you're introducing quite a bit of ambiguity.  You've made PT0S mean 
> "don't care" and "live forever".  You've also introduced this notion 
> of "wishing to share" - this should never be an option.  Short hand 
> notations is one thing - but saying "dunno" is something very different and 
> not something we have in the spec today and I'm not infavor of adding it. 
> 
> > GrantedExpires MUST NOT use the value PT0S, as 
> > that doesn't tell the subscriber anything useful. 
> 
> I disagree that GrantedExpires/PT0S isn't useful.  Its very clear that 
> the Suscription will not expire.  This says nothing about other 
> subscription mgmt logic - it just touches on the timeout part of it. 
> 
> > If the 
> > subscription manager either can not or will not tell the subscriber 
> > when the subscription will be automatically deleted (i.e. it does 
> > not support the negotiation of a subscription expiration) it 
> > generates the wse:ExpiresNotSupported fault.
> 
> Disagree with this too.  We're asking for an interop problem if 
> the two sides are not clear on when a subscription will be deleted 
> due to this timeout/expiry logic.  Even if its to say "it won't be". 
> 
> Overall I disagree that anything in the spec today introduces the 
> concept of not caring about this timeout stuff, or not negotiating it. 
> And I think it would be a mistake to introduce it now. Even missing 
> elements that imply "never expire" are still negotiating are 
> communicating the agreed to values of the timeout. 
> 
> It would really help me if we could back this discussion up and 
> you could point out the parts of the spec that are unclear or 
> introduce the ambiguity you're concerned about.  I don't see 
> where it says "no Expires", or PT0S, means "dunno".   
> 
> As I said above, if the terms we use in some spots need to be 
> tweaked then we should do so - but regardless of the wording 
> we're using I think the intent was that the absence of the 
> Expires/GrantedExpires elements (and PT0S) means "will not be 
> deleted due to time". 
> 
> -Doug 
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Take care:

    Dr. David Snelling < David . Snelling . UK . Fujitsu . com >
    Fujitsu Laboratories of Europe Limited
    Hayes Park Central
    Hayes End Road
    Hayes, Middlesex  UB4 8FE
    Reg. No. 4153469

    +44-7590-293439 (Mobile)



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Received on Tuesday, 5 October 2010 12:11:59 GMT

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