Re: [netmod] Order of evaluation for when?

[Andy Bierman]

On Sat, Oct 24, 2015 at 6:07 AM, Martin Bjorklund  wrote:

> Juergen Schoenwaelder  wrote:
> > On Fri, Oct 23, 2015 at 10:35:48AM +0200, Ladislav Lhotka wrote:
> > > Martin Bjorklund  writes:
> > >
> > > > auto-deletion in choice/when should be described as a property of the
> > > > data model for the datastore.  Parts of the text from Section 8.2.2
> > > > should be made more generic and moved, probably to a new section
> > > > 8.1.1.   I will have a look at this.
> >
> > [...]
> >
> > > IMO YANG spec should tell what's valid and what isn't, and stop there.
> >
> > As technical contributor, I tend to agree. The purpose of validation
> > should be to return a boolean - datastore is valid or invalid.
>
> Right.  This is what "must" does.  "when" is different.  If a node's
> "when" expression becomes false, that node is deleted, and its other
> constraints are no longer used (e.g. must, mandatory etc).  These are
> two different use cases, two different tools available to the data
> model designer.
>
> If we put "when" to the side for a moment, do you also think that
> there should be no auto-deletion of cases in a choice?
>
> If this discussion had started from implementation/deployment
> experience that said that "when" could not be implemented or that it
> made it difficult to write NMS system or something else, things would
> be different.  But now we have a feature that has been in use for 5+
> years, and there are several implementations of it out there, and now
> we say that it should be removed?  Or worse, keep the syntax but
> radically change the semantics.
>
>

The one special case that has been identified is data provided
as part of an edit that is silently deleted and  returned.
This could be considered different than providing an edit that
deletes existing data nodes.



> This said, I am all for guidelines and that we check for bad uses of
> "when" when we do reviews of data models.
>
>
We will do that, but it does not address the runtime error (or not)
of auto-deletion of data provided in the edit. Should this be
an error, a warning, or return OK?

Auto-deletion of existing data nodes is fine.
The client needs to be aware of the YANG module
or watch netconf-config-change notifications.  Setting /X=3 or /X=5
requires understanding of the semantics for object X.  The when-stmt is just
part of that requirement.




>
> /martin
>
>

Andy


>
>
> > I find
> > the idea scary that validation causes changes of a datastore in an
> > attempt to make an invalid the datastore valid. And it is even more
> > scary if the attempt to make the datastore valid requires to remember
> > what the last edit was that triggered the validation procedure in
> > order to decide how to try to make the datastore valid (if we consider
> > different protocols with different primitives to trigger edits on a
> > datastore).
> >
> > /js
> >
> > --
> > Juergen Schoenwaelder   Jacobs University Bremen gGmbH
> > Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
> > Fax:   +49 421 200 3103 
> >
>
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Re: [netmod] Order of evaluation for when?

[Martin Bjorklund]

Juergen Schoenwaelder  wrote:
> On Fri, Oct 23, 2015 at 10:35:48AM +0200, Ladislav Lhotka wrote:
> > Martin Bjorklund  writes:
> > 
> > > auto-deletion in choice/when should be described as a property of the
> > > data model for the datastore.  Parts of the text from Section 8.2.2
> > > should be made more generic and moved, probably to a new section
> > > 8.1.1.   I will have a look at this.
> 
> [...]
> 
> > IMO YANG spec should tell what's valid and what isn't, and stop there.
> 
> As technical contributor, I tend to agree. The purpose of validation
> should be to return a boolean - datastore is valid or invalid.

Right.  This is what "must" does.  "when" is different.  If a node's
"when" expression becomes false, that node is deleted, and its other
constraints are no longer used (e.g. must, mandatory etc).  These are
two different use cases, two different tools available to the data
model designer.

If we put "when" to the side for a moment, do you also think that
there should be no auto-deletion of cases in a choice?

If this discussion had started from implementation/deployment
experience that said that "when" could not be implemented or that it
made it difficult to write NMS system or something else, things would
be different.  But now we have a feature that has been in use for 5+
years, and there are several implementations of it out there, and now
we say that it should be removed?  Or worse, keep the syntax but
radically change the semantics.

This said, I am all for guidelines and that we check for bad uses of
"when" when we do reviews of data models.


/martin



> I find
> the idea scary that validation causes changes of a datastore in an
> attempt to make an invalid the datastore valid. And it is even more
> scary if the attempt to make the datastore valid requires to remember
> what the last edit was that triggered the validation procedure in
> order to decide how to try to make the datastore valid (if we consider
> different protocols with different primitives to trigger edits on a
> datastore).
> 
> /js
> 
> -- 
> Juergen Schoenwaelder   Jacobs University Bremen gGmbH
> Phone: +49 421 200 3587 Campus Ring 1 | 28759 Bremen | Germany
> Fax:   +49 421 200 3103 
> 

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Re: [netmod] preliminary agenda for yokohama posted

[Kent Watsen]

Here’s an update to the agenda for the two sessions at 94:

Updates:
  - syslog removed (because it’s ready for Last Call)
  - diffserv removed (nothing to report)
  - models moved to morning slot
  - times and presenters locked in (almost)

https://www.ietf.org/proceedings/94/agenda/agenda-94-netmod
- don’t forget to refresh your cache ;)

Thanks,
Kent and Tom


From: netmod > on 
behalf of Kent Watsen >
Date: Monday, October 19, 2015 at 8:39 PM
To: "netmod@ietf.org" 
>
Subject: [netmod] preliminary agenda for yokohama posted


The preliminary agenda for the two sessions at Yokohama has been posted here:

https://www.ietf.org/proceedings/94/agenda/agenda-94-netmod

Obviously a lot of unknowns, but that's what "preliminary" means right?  ;)

Kent   // chair hat on

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