[mpls] Use of schema mounts for common model

["Tarek Saad (tsaad)" <[e-mail]>]

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

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?

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.