Re: [netmod] Y34 - root node

[Andy Bierman <[e-mail]>]

On Mon, Aug 3, 2015 at 7:48 AM, t.petch <[e-mail]> wrote:

> ----- Original Message -----
> From: "Andy Bierman" <[e-mail]>
> To: "Acee Lindem (acee)" <[e-mail]>
> Cc: "NETMOD Working Group" <[e-mail]>
> Sent: Saturday, August 01, 2015 7:05 PM
> Subject: Re: [netmod] Y34
> On Sat, Aug 1, 2015 at 9:51 AM, Acee Lindem (acee) <[e-mail]>
> wrote:
>
> > Hi Juergen,
> >
> > On 8/1/15, 2:51 AM,  [e-mail]> wrote:
> >
> > >On Fri, Jul 31, 2015 at 12:46:49PM -0400, Lou Berger wrote:
> > >> Andy,
> > >>
> > >> On 07/27/2015 12:58 PM, Andy Bierman wrote:
> > >> > Hi,
> > >> >
> > >> > I don't think a standard for relocating subtrees would be worth
> it.
> > >> > I am not in favor of moving /interfaces or /system to a new
> location.
> > >> > That's not how YANG works. It only allows "obsolete and start
> over".
> > >> >
> > >> > I would suggest pursuing solutions that don't cause
> > >> > as much disruption and expense as possible.
> > >> >
> > >> I think it would be really good to explore other, less "disruptive"
> > >> options.
> > >
> > >I think the first step is to find out whether there is a problem
> worth
> > >to be fixed. Why are the RFCs in question broken? (Yes, I have read
> > >the openconfig IDs,
> >
> > Section 1.1 in
> > https://www.ietf.org/id/draft-openconfig-netmod-model-structure-00.txt
> > lists the goals of a generic model structure that will accommodate
> most
> > modern network devices. I guess you don’t agree that these are
> desirable?
>
> The only objection I have to this draft is the insertion of a top-level
> root
> called "device".  (Might as well be called "self").
> There are no sibling nodes planned or intended for
> this node, so it serves as an extra document root.
>
> <tp>
> One aspect of YANG I have never grasped is what a root means, if
> anything.
>
> I understand that it is needed for NETCONF (filters) and for YANG
> (augments, constraints) and so must be somewhere and must be relatively
> stable, but has it any other significance in the data model?
>
> As you may recall, I was involved with SMI first, where the root is
> somewhere up in the sky and life only becomes interesting some six
> levels down the hierarchy and that may colour my thinking.
>
>

YANG does a poor job of defining the root for YANG data nodes.
It is sometimes called a datastore (in the abstract).
Technically, YANG borrows the definition from XPath.
YANG just defines top-level data nodes and the parent of
these nodes is the document root.

There is no protocol or encoding neutral definition,
only an XML-specific definition.



> Tom Petch
>

Andy


>
>
> The well-specified XPath and YANG root (/) can be
> accessed by all protocol operations, exactly the same
> as a node called 'device'.  The actual node name will
> depend on the RPC function (e.g. 'data' or 'config').
>
> This is more than redundant however.  It introduces a "super-module"
> into YANG that every other module is expected to augment.
> YANG is intended to be more loosely coupled than that.
> This introduces an extra node and namespace declaration
> in all protocol messages, increasing message sizes.
>
> It also assumes all existing YANG models will get rewritten to
> account for "/device" in all path and XPath expressions.
> This is highly disruptive to existing deployments.
> Also, multiple data models to edit the same thing causes lots
> of extra complexity in the server (supporting both old
> location and new location).
>
> IMO a resource directory approach is much more realistic.
> The /device tree can contain all the organized NP containers.
> Instead of all the actual data nodes, this tree just has pointers
> to the real location of the resource. (like 301 Moved Permanently)
>
> Thanks,
> > Acee
> >
> >
> >
> Andy
>
>
>