Re: [mpls] [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?

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?
>
>
>     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.
>
>
>
>
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