Re: [mpls] [Teas] [netmod] Use of schema mounts for common model

We still hope that schema mount can handle cross-referencing across mounted
modules. It is also needed when ietf-interfaces model is mounted to
logical-network-element  and network-instance models.

More comments for this case below in-line.

Thanks,

- Xufeng

> -----Original Message-----
> From: Teas [mailto:teas-bounces@ietf.org] On Behalf Of Joel M. Halpern
> Sent: Friday, April 29, 2016 1:05 PM
> To: Tarek Saad (tsaad) <tsaad@cisco.com>; Martin Bjorklund
<mbj@tail-f.com>
> Cc: draft-ietf-teas-yang-te@ietf.org; mpls@ietf.org; teas@ietf.org;
> netmod@ietf.org; draft-ietf-netmod-schema-mount@ietf.org
> Subject: Re: [Teas] [netmod] Use of schema mounts for common model
> 
> With regard to leafrefs trying to point into groupings, would
instance-identifiers
> work for your use case?
> 

In this case, it would be hard to specify the must conditions for these
instance-identifiers to make them always applicable when the groupings are
used in various situations. If we are willing to re-structure everything,
the method used in draft-halpern-supa-generic-policy-data-model could be an
option to explore. 

> Yours,
> Joel
> 
> On 4/29/16 12:17 PM, Tarek Saad (tsaad) wrote:
> > Thanks Martin, please see inline..
> >
> >
> > On 2016-04-29, 6:29 AM, "Martin Bjorklund" <mbj@tail-f.com
> > <mailto:mbj@tail-f.com>> wrote:
> >
> >     "Tarek Saad (tsaad)" <tsaad@cisco.com <mailto:tsaad@cisco.com>>
wrote:
> >
> >         Hi authors/WG,
> >         In draft-ietf-teas-yang-te, we are driving the definition for a
> >         generic TE YANG model that can/may be used (and extended when
> >         necessary) for different data plane technologies (e.g. MPLS,
> >         OTN, WDM,
> >         etc.).
> >         Reviewing the schema mount idea presented in
> >         draft-ietf-netmod-schema-mount, we are thinking this proposal is
> >         useful and can facilitate the reuse of the our model in multiple
> >         places in the YANG tree (once per each technology), e.g.:
> >         ./mpls/mount-points/mount-point/module=ietf-te.yang
> >         ./otn/mount-points/mount-point/module=ietf-te.yang
> >
> >
> >     Schema mount is probably not the right solution to your problem.  I
> >     think a better solution in your case is to define groupings.
> >     Groupings are designed to be re-used at different places in the
> >     hierarchy.
> >
> >
> > We thought of this earlier, and found groupings pose their own set of
> > challenges too.. Specifically:
> > - a groupings with leafrefs could not reference data nodes that reside
> > in another grouping
> > - a grouping with leafrefs of relative path were challenge when the
> > relative path references data nodes outside the grouping
> > - the augmentation of the grouping by other modules is not as
> > straightforward
> >
> > That said, the grouping proposal seems to
> >
> > one could also think that with groupings one could address reuse of
> > the a model (e.g. Ietf-interfaces) for logical devices or VM (see
> > below). In fact, in your draft (section 2) you explicitly discourage
> > this approach as not scalable solution
> >
> >
> >    With the "uses" approach, ietf-interfaces would have to define a
> >    grouping with all its nodes, and the new model for logical devices
> >    would have to use this grouping.  This is a not a scalable solution,
> >    since every time there is a new model defined, we would have to
> >    update our model for logical devices to use a grouping from the new
> >    model.  Another problem is that this approach cannot handle vendor-
> >
> >
> >
> >         We have a comment/concern/suggestion and we value your feedback.
> >         The generic TE model currently references data nodes in the
global
> >         tree (e.g. from the ietf-interfaces model to define additional
TE
> >         properties associated with a specific device interface). Our
> >         understanding after reading section 3.1 of your draft is the
mounted
> >         model can *not* reference any data nodes outside the scope of
the
> >         mount-point (e.g. global data nodes in the yang tree). This
poses a
> >         limitation for us, do you have a suggestion for this problem?
> >         One possible solution we thought of was to replace the leaf-refs
> >         pointing to the global data nodes (e.g. Ietf-interfaces) with
> >         context
> >         names (e.g. the interface name).. This decouples the data-nodes
> >         defined in the TE generic model from those in the global tree
> >         (e.g. the actual interface ietf-interfaces model). Any feedback
on
> >         this or better suggestions?
> >
In this case, there are multiple augmentations to ietf-te.yang, such as
ietf-rsvp-te and ietf-sr-te. If ietf-te is a grouping, we cannot do the
augmentations before ietf-te is used. Using the grouping would be very
awkward when ietf-te is used. We would have to make the same many
augmentations at that time. Even worse, there could be future augmentations,
we cannot specify these augmentations now because they are not defined yet.

> >
> >     If you use groupings instead, you can still use proper leafrefs.
> >
> >
> > Not in all cases - as described above.
> >
> > Regards,
> > Tarek
> >
> >
> >
> >     /martin
> >
> >
> >
> >         Regards,
> >         Tarek
> >         Excerpt from draft-ietf-netmod-schema-mount
> >         3.1<https://tools.ietf.org/html/draft-ietf-netmod-schema-mount-
> 01#section-3.1>.
> >         Augment and Validation in Mounted Data
> >             All paths (in leafrefs, instance-identifiers, XPath
> >         expressions, and
> >             target nodes of augments) in the data models mounted at a
> >         mount point
> >             are interpreted with the mount point as the root node, and
the
> >             mounted data nodes as its children.  This means that data
> >         within a
> >             mounted subtree can never refer to data outside of this
subtree.
> >
> >
> >
> >
> > _______________________________________________
> > netmod mailing list
> > netmod@ietf.org
> > https://www.ietf.org/mailman/listinfo/netmod
> >
> 
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