Re: [netmod] evaluation of "when" under NMDA

Ladislav Lhotka <> Tue, 05 December 2017 09:03 UTC

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From: Ladislav Lhotka <>
To: Juergen Schoenwaelder <>
Date: Tue, 05 Dec 2017 10:03:07 +0100
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Subject: Re: [netmod] evaluation of "when" under NMDA
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On Mon, 2017-12-04 at 21:00 +0100, Juergen Schoenwaelder wrote:
> On Mon, Dec 04, 2017 at 07:09:51PM +0100, Ladislav Lhotka wrote:
> > 
> > Well, according to draft-ietf-netmod-revised-datastores-07:
> > 
> >    o  datastore schema: The combined set of schema nodes for all modules
> >       supported by a particular datastore, taking into consideration any
> >       deviations and enabled features for that datastore.
> > 
> > And "when" determines whether a given schema node is valid or
> > not. So if a schema node is invalid in the schema of <operational>
> > but valid in the schema of <intended>, then the former can hardly be
> > a superset of the latter.
> I do not follow your notion of 'schema node is valid or not'. Where is
> this concept defined? I think RFC 7950 talks about validation of data

Guess what, this notion is used in the definition of "when" statement (sec.

   The "when" statement makes its parent data definition statement
   conditional.  The node defined by the parent data definition
   statement is only valid when the condition specified by the "when"
   statement is satisfied. ...

This text clearly talks about a schema node, because it is what data definition
statements define.

> trees against a "schema". Perhaps there are places where the wording
> is not clear enough? I know that there are places where the RFC 7950
> text says just "node" without being explicit about the distinction
> between schema node and corresponding data nodes. If this is an issue

Note that data node is just a special type of schema node (sec. 3).

> here, we may consider posting erratas to clear things up.

Right, the text above could say "The schema node defined ..." but it can never
say "an instance of a data node" because "when" can also be used for "choice",
"case" and "augment", and then there is no conditional (parent) instance.


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