Re: [netmod] yang-data-ext issues

Martin Bjorklund <mbj@tail-f.com> Mon, 23 April 2018 20:08 UTC

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Subject: Re: [netmod] yang-data-ext issues
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Andy Bierman <andy@yumaworks.com>; wrote:
> > ....
> > >
> > > I do not understand the need for a yang-data structure that represents
> > data
> > > that can be instantiated anywhere and everywhere.
> >
> > AFAIK noone is proposing that.
> >
> > > I do not want to break
> > > existing tools that expect sibling data nodes in the same module
> > namespace
> > > to
> > > be unique local-names.
> > >
> > > I would rather stick with the yang-data in RFC 8040 than introduce a new
> > > extension
> > > with no restrictions.  Standard YANG extensions should be interoperable
> > and
> > > have
> > > a clear purpose.
> >
> > Of course.
> >
> > > If we do not need to define what a YANG extension does in
> > > a way that can be observed somehow, then it does not need to be a
> > standard.
> >
> > Agreed.
> >
> > Not sure how any of this helps with the original issue though.
> >
> >
> 
> You proposed that duplicate nodes were OK:
> 
> module X {
> prefix x;
> 
> x:yang-data A {
>    list foo { ... }
> }
> 
> x:yang-data B {
>   container foo { ... }
> }
> 
> }
> 
> 
> I do not want to allow any duplicates.

Yes, I got that.

> There are no encoding and parsing rules for instance data
> that support this sort of duplicate.

This is not correct, as I have demonstrated earlier, and I think you
also accepted; if different structures are defined for different rpcs'
error-infos, then these structures can have the same child node names.

I think that we have to agree on the basics before disussing
solutions:

  1)  Should we do anything at all?

      (i.e., keep using yang-data in RFC 8040)

  2)  Should we define structures that only can be used in
      standalone instance documents?

      (i.e., *more* restrictive than yang-data in RFC 8040)

  3)  Should we define structures that can be used in standalone
      instance documents, error-info contents, and other places that
      we might not know right now?

      (i.e., *less* restrictive than yang-data in RFC 8040)


Since the current draft says:

   The "yang-data" extension statement from RFC
   8040 [RFC8040] is defined for this purpose, however it is limited in
   its functionality.

   The intended use of the "yang-data" extension is to model all or part
   of a protocol message, such as the "errors" definition in ietf-
   restconf.yang [RFC8040], or the contents of a file.  However,
   protocols are often layered such that the header or payload portions
   of the message can be extended by external documents.  The YANG
   statements that model a protocol need to support this extensibility
   that is already found in that protocol.


I thought we are doing (3).



/martin



> yang-data definitions define conceptual data nodes (e.g, /x:foo)
> Only one data-def-stmt (in yang-data or otherwise) can define a data node
> /x:foo.
> The descriptive names for the yang-data (A or B) do not define namespaces.
> 
> 
> 
> > /martin
> >
> >
> Andy