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

[Robert Wilton <[e-mail]>]

On 04/12/2017 17:47, Andy Bierman wrote:
>
>
> On Mon, Dec 4, 2017 at 9:05 AM, Ladislav Lhotka <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     On Mon, 2017-12-04 at 17:34 +0100, Martin Bjorklund wrote:
>     > Ladislav Lhotka <[e-mail] <mailto:[e-mail]>> 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>.
>
>
>
> I see your point now.
> The server has to evaluate the when-stmts in operational.

I think that this is probably down to implementation, but I don't think 
that this is necessarily required.  A server is meant to conform to 
'when' statements in <operational> (e.g. if the system is in a normal 
steady state), but they are allowed to be violated, and I'm not 
expecting that a server would evaluate them (except perhaps to discover 
implementation bugs).  Further, if violations of when statements in 
<operational> are detected then I don't think that there is anything 
that the server can reasonable do.


> Even though the schema trees are the same, the client has a complex 
> task comparing
> <intended> to <operational>.

I don't get why this isn't just a simple diff between the <intended> and 
<operational> data trees.  What is causing the complexity?

Thanks,
Rob


> However it is no different than the existing
> complexity comparing <candidate> to <running>.
>
>     Lada
>
>
> Andy
>
>     >
>     > > RFC 7950 says in sec. 7.21.5 that the context node for XPath
>     evaluation is
>     >
>     > "the
>     > > augment's target node in the data tree", but with NMDA we have
>     multiple data
>     > > trees, hence multiple target nodes.
>     >
>     > We had multiple datastores even before NMDA.  The when expression
>     > could be true in candidate but false in running.
>     >
>     > /martin
>     --
>     Ladislav Lhotka
>     Head, CZ.NIC Labs
>     PGP Key ID: 0xB8F92B08A9F76C67
>
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