Subject: RE: [Simple] XCAP - node selector issue

From: "Bulent Gecer (KI/EAB)" <[email-masked]>
Date: Wed, 20 Oct 2004 10:28:26 +0200

Hi Jonathan,

Thanks for your quick reply, we are satisfied with the information you gave us.  

Now, we have another question that we already sent to the SIMPLE-list concerning namespace handling in XCAP.  We don't feel this is properly addressed in the XCAP-specification.  Are there any ongoing discussions on how to handle this?  The mail we are referring to has the subject "[Simple] XCAP - namespace handling".  Would you please have a look at it and give us your comments?

Thanks,

/Max Blommé & Bulent Gecer

-----Original Message-----
From: Jonathan Rosenberg [mailto:[email-masked]]
Sent: den 20 oktober 2004 02:34
To: Bulent Gecer (KI/EAB)
Cc: [email-masked]'; Anders Lindgren C (HF/EAB)
Subject: Re: [Simple] XCAP - node selector issue

Bulent,

Thanks for the comments. I am in the midst of revising xcap, with the 
hope that this revised version can go to IESG; WGLC ended some time 
back. If we can resolve these isssues ASAP, any fixes can be 
incorporated into the document before I revise it.

On this particular point, this was a previous open issue, XCAP issue 7, 
"Uniqueness at each hop". This specific point you raised, that an xpath 
implementation won't normally do this check, was discussed in the 
threads on the topic. There was rough consensus to introduce this 
constraint anyway, primarily because many folks were doing non-xpath 
based implementations, and the cost of not having this constraint is 
very high in this case. There were also performance concerns raised, as 
the expression evaluation can grow esponentially in the worst case if 
you do not introduce the constraint.

If you still wish to use an xpath implementation, there are ways to do 
so and still meet this constraint. You'd have to evaluate the expression 
step-wise, and verify that each step produces a single node.

As such, I am somewhat reluctant to reopen this issue unless you can 
provide some new data that was not presented in the previous thread.

Thanks,
Jonathan R.

Bulent Gecer (KI/EAB) wrote:

> Hi,
> 
> We have discovered an issue regarding node selectors in draft-ietf-simple-xcap-03.txt which we think needs to be addressed:
> 
> 
> Problem:	In the XCAP-specification page 20 paragraph 3, it says that "The node selector is only valid if a single element was selected.  This element 			becomes the context for the evaluation of the next step in the node selector expression.".  This means that for the following document,
> 
> 			<lists>
> 				<list name="friends">
> 			      	<entry uri="sip:[email-masked]"/>
> 					<entry uri="sip:[email-masked]"/>
> 				</list>      
> 			      <list name="enemies">
> 			      	<entry uri="sip:[email-masked]"/>
> 					<entry uri="sip:[email-masked]"/>
> 			      </list>
> 			 </lists>
> 
> 		the node selector 
> 				
> 			/lists/list/entry[@uri="sip:[email-masked]"] 
> 				
> 		would be invalid in XCAP since the second part of the node selector selects several elements.  This means that an existing XPATH-library cannot 		be used to implement XCAP since the node selector above is valid in XPATH.  This seems to be an unnecessary restriction.
> 
> Solution:	We suggest that for retrieve and delete operations, only the last part of the node selector needs to identify a single element.  On the other 			hand, for creating new elements, the part of the node selector selecting the parent of the new element needs to identify a single element.
> 
> 
> Comments please?
> 
> Regards,
> 
> /Max Blommé & Bulent Gecer
> 
> _______________________________________________
> Simple mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/simple
> 

-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Director, Service Provider VoIP Architecture   Parsippany, NJ 07054-2711
Cisco Systems
[email-masked]                        FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
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