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

[Ladislav Lhotka <[e-mail]>]

On Fri, 2018-11-23 at 13:39 +0100, Juergen Schoenwaelder wrote:
> On Fri, Nov 23, 2018 at 01:02:03PM +0100, Ladislav Lhotka wrote:
> > > Here is an attempt to rewrite things in a way according to how I
> > > understand things works. It should be possible to describe what we
> > > mean. If we can't do that, we have a bigger problem. (I have changed
> > > only the last two sentences.)
> > > 
> > > OLD
> > > 
> > >    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) 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.
> > > 
> > > NEW
> > > 
> > >    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) is used to identify a leaf or
> > >    leaf-list node in the data tree. The value space of the leafref
> > >    node is determined by the value space of the schema tree node
> > 
> > The term "value space of a schema tree node" is not defined.
> 
> OK. So we say 'the value space of the type of the schema tree node'.

Yes, this is better. But what if the schema tree node is made invalid due to a
failed "when" expression? Does it still apply?

>  
> > >    definining the referenced data tree node.
> > 
> > With require-instance=false there needn't be any referenced data tree node.
> 
> So we add "(irrespective whether the node exists or not).

If the data tree node doesn't exist, we cannot refer to the schema tree node
that defines it.

> 
> > > This likely is not perfect yet but perhaps we manage to make it
> > > perfect. ;-) What is not yet clearly described I think is what
> > > 'further restricted by corresponding instance nodes in the data tree'
> > > means (and that I think depends on require-instance). Perhaps add
> > 
> > Right. In this case it is not "further restricted" but rather there is a
> > discrete set of possible values.
> 
> A discrete set of possible values is a restriction so I do not
> understand your comment. So here is the next iteration:

If required-instance is true, there is no need to care about all this tricky
stuff with schema tree nodes and their types. In other words:

1. if required-instance = true, the permitted values are obtained from the data
tree.

2. if required-instance = false, the corresponding schema node has to be
determined, and its type defines the permitted values of the leafref node.

It is an exclusive-or, #1 is not an "optional further restriction".

Lada

> 
> NEW:
> 
>     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 (see
>     Section 9.9.3).  The "path" substatement (Section 9.9.2) is used
>     to identify a leaf or leaf-list node in the data tree. The value
>     space of the leafref node is determined by the value space of the
>     type of the schema tree node definining the referenced data tree
>     node (irrespective whether the referenced data tree node exists or
>     not).
> 
> /js
> 
-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67