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

[Ladislav Lhotka <[e-mail]>]

On Fri, 2018-11-23 at 10:38 +0100, Juergen Schoenwaelder wrote:
> On Fri, Nov 23, 2018 at 10:22:11AM +0100, Ladislav Lhotka wrote:
> > Juergen Schoenwaelder <[e-mail]> writes:
> > 
> > > On Thu, Nov 22, 2018 at 03:00:27PM +0100, Martin Bjorklund wrote:
> > > > Andy Bierman <[e-mail]> 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??

It is certainly more correct than "data tree". The assumption is that the "path"
statement (that by definition selects some instance nodes in the data tree) also
implicitly points to a leaf or leaf-list node iin the schema tree.

> 
> 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?

There are two problems with it:

1. There may be no such schema node, because it can be possibly invalidated by a
"when" expression.

2. The term "value space" is not defined.

Lada

> 
> /js
> 
-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67