Re: [netmod] yang-data-ext issues

Andy Bierman <andy@yumaworks.com> Fri, 27 April 2018 00:52 UTC

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From: Andy Bierman <andy@yumaworks.com>
Date: Thu, 26 Apr 2018 17:52:00 -0700
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To: Andy Bierman <andy@yumaworks.com>, NetMod WG <netmod@ietf.org>
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Subject: Re: [netmod] yang-data-ext issues
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On Wed, Apr 25, 2018 at 10:53 PM, Ladislav Lhotka <lhotka@nic.cz>; wrote:

> Ladislav Lhotka <lhotka@nic.cz>; writes:
>
> > On Wed, 2018-04-25 at 08:04 -0700, Andy Bierman wrote:
> >>
> >>
> >> On Wed, Apr 25, 2018 at 7:05 AM, Ladislav Lhotka <lhotka@nic.cz>; wrote:
> >> > On Wed, 2018-04-25 at 15:55 +0200, Juergen Schoenwaelder wrote:
> >> > > On Tue, Apr 24, 2018 at 04:36:01PM +0200, Martin Bjorklund wrote:
> >> > > > Ladislav Lhotka <lhotka@nic.cz>; wrote:
> >> > > > > Martin Bjorklund <mbj@tail-f.com>; writes:
> >> > > > >
> >> > > > > > Hi,
> >> > > > > >
> >> > > > > > I am not sure what this statement tells us re. the issue in
> this
> >> > email
> >> > > > > > thread.
> >> > > > >
> >> > > > > It tells us that, in my view, the approach taken in this
> document is a
> >> > > > > bad idea.
> >> > > >
> >> > > > Do you mean that the WG shoud drop this document?  And people that
> >> > > > need yang-data should continue to use the version in 8040?  Or
> that
> >> > > > people that need yang-data do not have a valid use case and they
> >> > > > should do something else?
> >> > >
> >> > > One option is that people use yang-data as defined in RFC 8040 until
> >> >
> >> > IMO, people should use plain YANG. With the new YANG library it will
> be
> >> > possible
> >> > to confine such non-NM schemas in a special datastore so that the
> intention
> >> > should be clear and multi-module schemas with all the additional data
> >> > (versions,
> >> >  features, deviations) can be used.
> >> >
> >>
> >> I don't see how yang-data interferes with "plain YANG" at all.
> >> It is for data that is not in scope for plain YANG.
> >
> > My question is why this extension is needed in the first place.
>
> For example, RFC 8040 could have used two modules instead of
> "ietf-restconf", one with the contents of grouping "errors" and the
> other with the contents of grouping "restconf". No extension.
>
>
This is true. We used to do this before yang-data was available.



> What would be wrong with this solution? Instead, the reader is
> overwhelmed with the complexity of the "yang-data" definition, and most
> tools cannot process the module.
>

There are tools that can use yang-data.
Not all use-cases involve a server to query for a yang-library.
Offline tools need to know about the special data somehow.
The yang-data extension prevents data-def-stmts from being treated
as if they were configuration or operational data.

I agree with you that unconstrained use of yang-data is questionable
for a standard extension. The bar should be that all tools which choose
to implement the extension should provide the user with the same behavior.
Declaring that behavior out-of-scope does not help interoperability at all.



> Lada
>
>
Andy


> >
> >> A plain client can ignore yang-data and not affect and RPC,
> notification, or
> >> data
> >> definitions in plain YANG.
> >
> > A plain (NC/RC) client should never see such data even if it is not
> protected by
> > yang-data in YANG. On the other hand, tools will be able to process such
> schemas
> > (generate the ascii tree, convert it to something else, generate sample
> > instances etc.) without explicitly supporting yang-data.
> >
> > Lada
> >
> >>
> >>
> >> > Lada
> >> >
> >>
> >> Andy
> >>
> >> > > there is a version of YANG that has a proper and complete integrated
> >> > > solution. (If for example yang-data is used to declare error content
> >> > > for RPCs, then more extensions are needed or a proper integration
> into
> >> > > YANG. Is it really good to introduce augment-yang-data (instead of
> >> > > making augment work with say 'data' in YANG 1.2)? And then we do
> >> > > uses-yang-data etc.
> >> > >
> >> > > /js
> >> > >
> >> > --
> >> > Ladislav Lhotka
> >> > Head, CZ.NIC Labs
> >> > PGP Key ID: 0xB8F92B08A9F76C67
> >> >
> >> > _______________________________________________
> >> > netmod mailing list
> >> > netmod@ietf.org
> >> > https://www.ietf.org/mailman/listinfo/netmod
> >>
> >>
> > --
> > Ladislav Lhotka
> > Head, CZ.NIC Labs
> > PGP Key ID: 0xB8F92B08A9F76C67
> >
> > _______________________________________________
> > netmod mailing list
> > netmod@ietf.org
> > https://www.ietf.org/mailman/listinfo/netmod
>
> --
> Ladislav Lhotka
> Head, CZ.NIC Labs
> PGP Key ID: 0xB8F92B08A9F76C67
>