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

Martin Bjorklund <mbj@tail-f.com> writes:

> Ladislav Lhotka <lhotka@nic.cz> wrote:
>> On Mon, 2017-12-04 at 18:22 +0100, Juergen Schoenwaelder wrote:
>> > On Mon, Dec 04, 2017 at 06:05:58PM +0100, Ladislav Lhotka wrote:
>> > > On Mon, 2017-12-04 at 17:34 +0100, Martin Bjorklund wrote:
>> > > > Ladislav Lhotka <lhotka@nic.cz> wrote:
>> > > > > Hi,
>> > > > > 
>> > > > > if we have
>> > > > > 
>> > > > > augment "/target/node" {
>> > > > >   when "...";
>> > > > >   ...
>> > > > > }
>> > > > > 
>> > > > > is the "when" expression supposed to be evaluated separately in each
>> > > > 
>> > > > datastore,
>> > > > > and the augment applied only in those datastores where the result is
>> > > > > true?
>> > > > 
>> > > > Yes.
>> > > 
>> > > But then it cannot be guaranteed that the schema for <operational> is a
>> > > superset
>> > > of the schema of configuration datastores - the when expression can evaluate
>> > > to
>> > > false in <operational> but true in <intended>.
>> > > 
>> > 
>> > For me, its still the same schema - a when expression does not change
>> > my notion of 'schema'.
>
> Agreed.
>
>> 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.
>
> This text does not write that nodes with false when expressions are
> not considered part of the schema.
>
>> 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>
>
> They are still part of the schema.
>
> Again, it is a matter of terminology - when we say that the "schema"
> of <operational> is a superset of the "schema" of the conventional
> datastores, we do not exclude false when expressions from the
> "schema".  As per the defintion above we include the modules, their
> features and deviations in the term "schema".

My understanding was that superset means that the schema tree of
<intended> has to be a subtree of <operational> schema tree. The
paragraph in revised-datastores-07 seems to support this interpretation
as it talks about "YANG nodes omitted from <operational>", not about
modules, features and deviations:

   The datastore schema for <operational> MUST be a superset of the
   combined datastore schema used in all configuration datastores except
   that YANG nodes supported in a configuration datastore MAY be omitted
   from <operational> if a server is not able to accurately report them.

Lada

>
>
> /martin
>
>
>
>>, then the former can hardly be a superset of the latter.
>> 
>> Lada
>> 
>> > 
>> > /js
>> > 
>> -- 
>> Ladislav Lhotka
>> Head, CZ.NIC Labs
>> PGP Key ID: 0xB8F92B08A9F76C67
>> 
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>> 

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