Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC change?

Martin Bjorklund <mbj@tail-f.com> Fri, 23 November 2018 10:05 UTC

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From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] Adding a pre-existing leaf into a new 'choice' - NBC change?
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Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> On Fri, Nov 23, 2018 at 10:22:11AM +0100, Ladislav Lhotka wrote:
> > Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> writes:
> > 
> > > On Thu, Nov 22, 2018 at 03:00:27PM +0100, Martin Bjorklund wrote:
> > >> Andy Bierman <andy@yumaworks.com> wrote:
> > >> > 
> > >> > 9.9 <https://tools.ietf.org/html/rfc7950#section-9.9>.  The leafref
> > >> > Built-In Type
> > >> > 
> > >> >    The leafref built-in type is restricted to the value space of some
> > >> >    leaf or leaf-list node in the schema tree and optionally further
> > >> >    restricted by corresponding instance nodes in the data tree.  The
> > >> >    "path" substatement (Section 9.9.2
> > >> > <https://tools.ietf.org/html/rfc7950#section-9.9.2>) is used to
> > >> > identify the referred
> > >> >    leaf or leaf-list node in the schema tree.  The value space of the
> > >> >    referring node is the value space of the referred node.
> > >> 
> > >> Yes, it should be "data tree" in both occurrences.
> > >
> > > Time for an errata?
> > 
> > Here is the old discussion thread:
> > 
> > https://www.ietf.org/mail-archive/web/netmod/current/msg15979.html
> > 
> > Everything relevant had been extensively discussed in it, and I am
> > sceptical that we can come up with anything significantly better - it
> > will only be more (or different) hand-waving. The problem is inherent in
> > the leafref design introduced in YANG 1.1. It won't go away no matter
> > how much we paper over it.
> >
> 
> So you think the use of 'schema tree' in the text quoted above (is
> used to identify the referred leaf or leaf-list node in the schema
> tree) is correct??
> 
> I do not want to discuss whether you like the design of leafrefs or
> not here - at this time we should focus on whether the text is correct
> or not given the design we have. So again, you think that 'schema
> tree' is correct in the statement?

After reading the quoted thread and thinking some more, I think the
text in 9.9 is in fact correct.  As Lada wrote in that thread:
 
   2. It [path] also implicitly refers to a leaf node in the schema
      [...]

The problem is that this "implicit reference" isn't defined.  9.9
talks about reference to a schema node, and 9.9.2 talks about the data
tree, but there is no text that ties these together.


/martin