Re: [netmod] Clarification needed for YANG 1.1 XPATH context

Martin Bjorklund <mbj@tail-f.com> Thu, 25 February 2016 15:31 UTC

Date: Thu, 25 Feb 2016 16:31:05 +0100
Message-Id: <20160225.163105.511576225570588684.mbj@tail-f.com>
To: wivory@Brocade.com
From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] Clarification needed for YANG 1.1 XPATH context
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William Ivory <wivory@Brocade.com> wrote:
> 
> 
> -----Original Message-----
> From: Martin Bjorklund [mailto:mbj@tail-f.com] 
> Sent: 25 February 2016 15:17
> To: William Ivory <wivory@Brocade.com>
> Cc: netmod@ietf.org
> Subject: Re: [netmod] Clarification needed for YANG 1.1 XPATH context
> 
> William Ivory <wivory@Brocade.com> wrote:
> > Hi,
> > 
> > I'm looking for clarification on the meaning of the following 
> > paragraph in section 6.4.1 (XPATH context) in RFC6020bis:
> > 
> >    'If a node that exists in the accessible tree has a non-presence
> >    container as a child, then the non-presence container also exists in
> >    the tree.'
> > 
> > It's unclear to me what this is trying to say, and why - for example, 
> > does this mean that I need to validate any 'must' and 'when'
> > statements on the child container even when nothing within that child 
> > container is configured?
> 
> must expressions are always evaluated if the node where the must
> expression is defined exists, regardless of the number of children
> this node has.
> 
> [wivory] So in my example where the child container (non-presence) has
> NO children, then it doesn't exist, and any must statement on it
> should not be run.  Only when a non-presence container has a non-zero
> number of children should any 'must' statements on that container be
> run.
> 
> [wivory] If that's the case, then would it be correct to say that the
> intention of this paragraph is as a reminder that one must evaluate
> 'must' statements on nodes that have no inherent meaning and exist
> only because they contain child nodes?

No; section 7.5.3 says:

   When a datastore is validated, all "must" constraints are
   conceptually evaluated once for each node in the accessible tree (see
   Section 6.4.1).

And the quoted paragraph of 6.4.1 says that the NP-container
(conceptually) exists if its parent exists - regardless of number of
children.

So if the parent exists, any must expressions in the NP-container are
evaluated.


/martin

[netmod] Clarification needed for YANG 1.1 XPATH … William Ivory
Re: [netmod] Clarification needed for YANG 1.1 XP… Martin Bjorklund
Re: [netmod] Clarification needed for YANG 1.1 XP… William Ivory
Re: [netmod] Clarification needed for YANG 1.1 XP… Martin Bjorklund
Re: [netmod] Clarification needed for YANG 1.1 XP… William Ivory
Re: [netmod] Clarification needed for YANG 1.1 XP… Radek Krejčí
Re: [netmod] [yang-doctors] Clarification needed … Ladislav Lhotka