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

William Ivory <wivory@Brocade.com> Thu, 25 February 2016 15:25 UTC

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From: William Ivory <wivory@Brocade.com>
To: Martin Bjorklund <mbj@tail-f.com>
Thread-Topic: [netmod] Clarification needed for YANG 1.1 XPATH context
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Date: Thu, 25 Feb 2016 15:25:39 +0000
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Cc: "netmod@ietf.org" <netmod@ietf.org>
Subject: Re: [netmod] Clarification needed for YANG 1.1 XPATH context
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-----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?

Thanks,

William


/martin

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