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RE: too many extension points (was Re: [Bug 6692] New: Remove Mode from the specification)

From: Chou, Wu (Wu) <wuchou@avaya.com>
Date: Fri, 10 Apr 2009 10:03:11 -0400
Message-ID: <F81BDFA28AE48D4793E253362D1F7A740112AB36@300813ANEX2.global.avaya.com>
To: "Gilbert Pilz" <gilbert.pilz@oracle.com>, "David Snelling" <David.Snelling@UK.Fujitsu.com>
Cc: <public-ws-resource-access@w3.org>, "Doug Davis" <dug@us.ibm.com>, "Bob Freund" <bob.freund@hitachisoftware.com>, "Li, Li (Li)" <lli5@avaya.com>
Sorry to be repetitive.
 
The current WS-E specs fully support using all the other options
described in Gil and Dave emails. To use SOAP header or the Mode
attribute of WS-E is an implementation choice, and an implementation can
choose one or even use both for the application needs.
 
However, removing Mode attribute/fault of WS-E (issue 6692) will force
implementation to only use SOAP header, and break the existing WS-E
applications and implementations that follow the current WS-E specs
(detailed comments are in
http://lists.w3.org/Archives/Public/public-ws-resource-access/2009Apr/00
33.html )
 
Thanks,
 
- Wu Chou.

________________________________

From: Gilbert Pilz [mailto:gilbert.pilz@oracle.com] 
Sent: Thursday, April 09, 2009 3:33 PM
To: David Snelling
Cc: Chou, Wu (Wu); public-ws-resource-access@w3.org; Doug Davis; Bob
Freund; Li, Li (Li)
Subject: Re: too many extension points (was Re: [Bug 6692] New: Remove
Mode from the specification)


Another place where @Mode is inferior is in the dynamic support of
extensions. For example, suppose I am an Event Sink that, for whatever
reasons, would prefer to acknowledge Notifications but would still be
willing to create a subscription even if the Event Source didn't support
acks (you can substitute any flavor of extension here). Using @Mode you
would have to:

1.) send a Subscribe request with the "PushWithAcks" mode
2.) handle the resulting "mode not understood" fault
3.) send a Subscribe request w/out the "PushWithAcks" mode

You have to do this because of @Mode's "fault on non-understood"
semantics. Using standard, XML extension mechanisms and our new, "ignore
extensions you don't understand" model, you could define an extension to
wse:Subscribe that meant "PushWithAcks" and a corresponding extension to
wse:SubscribeResponse that meant "AcceptPushWithAcks". Now all you have
to do to support the optional use of acks is to

1.) send a Subscribe request with the "PushWithAcks" extension
2.) look at the SubscribeResponse - if it doesn't contain a
"AcceptPushWithAcks" extension then the Event Source  didn't understand
the request to accept/process acks for Notifications

Same result as above with one less round trip. Of course, as has been
mentioned numerous times before, if the Event Sink wanted the "don't
create the subscription if you don't understand this extension"
behavior, it could include a "UsingPushWithAcks" SOAP Header with
@mustUnderstand="1".

- gp

David Snelling wrote: 

	Gil, 

	Thanks for this discussion. It also brought something back to my
mind that has worried me about Mode. If in the end we keep it, it will
need to be enhanced to provide even the minimal required support.
Reasoning follows, very incomplete at this stage, but would form the
basis of a new issue should we retain Mode.

	So assuming Mode stays, we should encourage (at least SHOLD) ALL
extensions to the semantics of Eventing to use the same mechanism. As
soon as this logical step takes place, meeting the simple queuing use
case becomes problematic not to mention more interesting cases. Where do
we put queuing limits etc? The Mode attribute is only a URI. As Gil
points out there are a number of places to stuff extension information,
but to support Mode properly, we would need a
<wse:PutModeExtensionDataHere/> element so people could use the
extension points consistently.

	I don't want this can of worms opened at all, as the
specification starts to become very complicated (folks from the
WS-Notification WG will remember painful discussions when this kind of
bloat was discussed there). Eventing is a really good simple
specification with clean semantics. Retaining Mode in (a clean and
functional manner) will probably change all that.

	Please let's get rid of Mode.


	On 03 Apr 2009, at 21:31, Gilbert Pilz wrote:


		Let's look at the schema for the wse:Subscribe message
and it's included DeliveryType element (I've taken the liberty of
highlighting the existing extension points - you need to view this as
HTML to see what I'm talking about):
		
		<xs:element name="Subscribe">
		  <xs:complexType>
		    <xs:sequence>
		      <xs:element name="EndTo"
type="wsa:EndpointReferenceType"
		
		                  minOccurs="0" />
		      <xs:element name="Delivery"
type="tns:DeliveryType" />
		      <xs:element name="Expires"
type="tns:ExpirationType"
		
		                  minOccurs="0" />
		      <xs:element name="Filter" type="tns:FilterType"
		
		                  minOccurs="0" />
		      <xs:any namespace="##other" processContents="lax"
		
		              minOccurs="0" maxOccurs="unbounded" />
		    </xs:sequence>
		    <xs:anyAttribute namespace="##other"
processContents="lax" />
		  </xs:complexType>
		</xs:element>
		
		<xs:complexType name="DeliveryType" mixed="true">
		  <xs:sequence>
		    <xs:element ref="wse:NotifyTo" minOccurs="0"
maxOccurs="1" />
		    <xs:any namespace="##any" processContents="lax"
		            minOccurs="0" maxOccurs="unbounded" />
		  </xs:sequence>
		  <xs:attribute name="Mode" type="xs:anyURI"
use="optional"
	
default="http://schemas.xmlsoap.org/ws/2004/08/eventing/DeliveryModes/Pu
sh" />
		  <xs:anyAttribute namespace="##other"
processContents="lax" />
		</xs:complexType>
		    
		If I was a developer interested in extending
WS-Eventing, I would find this situation confusing. Ignoring the fact
that the wse:NotifyTo element is an EPR and can itself be extended,
there are five (5) different ways I can extend the wse:Subscribe message
(or, if you count element/attribute extension of the same element as a
"single way", there are three (3)). What makes this even more confusing
is that not all of these extension points have the same processing
rules. The XML extension points (in black-bold) are subject to the
following, recently accepted, language:
		

			The elements defined in this specification MAY
be extended at the points
			indicated by their outlines and schema.
Implementations MAY add child elements
			and/or attributes at the indicated extension
points but MUST NOT contradict the
			semantics of the parent and/or owner,
respectively. If a receiver does not
			recognize an extension, the receiver SHOULD
ignore that extension. Senders MAY
			indicate the presence of an extension that has
to be understood through the use
			of a corresponding SOAP Header with a
soap:mustUnderstand attribute with the
			value "1".
			  

		Whereas the WS-Eventing specific extension point (in
blue-bold) is subject to the following:
		

			If the event source does not support the
requested delivery mode, the request MUST fail, and the event source MAY
generate a wse:DeliveryModeRequestedUnavailable fault indicating that
the requested delivery mode is not supported.
			

		I think the common reaction to this situation would be
"WTF <http://thedailywtf.com/Default.aspx> ?" This needs to be
simplified so that, if you want to extend WS-Eventing, you aren't
required to navigate through a maze of different extension points that
may or may not result in different processing behavior (i.e. "What is
the difference between extending /wse:Subscibe/wse:Delivery or just
/wse:Subscribe?").
		
		Clearly the "Mode" attribute, with its conflicting
semantics, should be removed. In addition to this, we need to remove the
"Delivery" element and it's extension points (obviously we would move
the wse:NotifyTo element up into the wse:Subscribe element). What we
would be left with would look like this:
		
		<xs:element name="Subscribe">
		  <xs:complexType>
		    <xs:sequence>
		      <xs:element ref="wse:NotifyTo" minOccurs="0"
maxOccurs="1" />
		      <xs:element name="EndTo"
type="wsa:EndpointReferenceType"
		
		                  minOccurs="0" />
		      <xs:element name="Expires"
type="tns:ExpirationType"
		
		                  minOccurs="0" />
		      <xs:element name="Filter" type="tns:FilterType"
		
		                  minOccurs="0" />
		      <xs:any namespace="##other" processContents="lax"
		
		              minOccurs="0" maxOccurs="unbounded" />
		    </xs:sequence>
		    <xs:anyAttribute namespace="##other"
processContents="lax" />
		  </xs:complexType>
		</xs:element>
		What you have now is really two ways to extend the
wse:Subscribe request. You can extend the wse:Subscribe message (through
either an attribute or an element) if you want an extension that is
specific to WS-Eventing, or you can extend the NotifyTo EPR if you want
an extension that operates at the WS-Addressing level (i.e. across any
technology that uses WS-Addressing).
		
		- gp
		
		Chou, Wu (Wu) wrote: 

			Doug,
			 
			Mode attribute in WS-E is to specify the
additional required event delivery behavior or required
application/business logic extensions that the event source must
understand/support before being allowed to accept the event
subscription.
			 
			My understanding is: "push_event_thru_proxy" is
for all events delivery from the Subscribe. As such, it covers
SubscriptionEnd event. The Mode attribute also allows to specify fine
grained application logic to control the event delivery.  If you want,
more fine grained event delivery logic/procedure can be easily added to
Mode attribute to control the event delivery, e.g.
"push_thru_proxy_for_subscriptionend_event_only",
"push_thru_proxy_for_non_subscriptionend_event", etc. 
			 
			Mode attribute in WS-E provides a standard
extension point to add application specific logic and behavior to event
delivery, so that it can enforce the required procedure/logic for
business applications when using WS-Eventing for event delivery.
			 
			Thanks,
			 
			- Wu Chou.
			 
			>Wu,
			 > since its too easy for things to get lost in
these long messages, let me 
			focus on one particular aspect of this.  
			 
			>Surely the idea of using a proxy 
			for sending messages is not WS-Eventing
specific.  How do you support 
			sending any other asynchronous message
(non-NotifyTo messages) thru a 
			proxy?  
			>Need a clarification on th, e.g. a general
question, a question for WS-E or a question for WS-E plus Mode.
			 
			>For example, the SubscriptionEnd message.
			
			thanks
			-Doug
			
			 
			 
			Wu Chou, IEEE Fellow, Ph.D. | Director |Dialogue
System Research | AVAYA | 233 Mt. Airy Road| Rm. 2D48 | Basking Ridge,
NJ 07920 | Voice/Fax: 908-696-5198 / 908-696-5401 | wuchou@avaya.com
<blocked::mailto:wuchou@avaya.com>  
			 


	
	
	
	
	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 Friday, 10 April 2009 14:03:59 UTC

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