[Netconf] Existence of Non-Presence Containers

["Gary Wu (garywu)" <[e-mail]>]

Hi NETCONF WG,

I have a question about the definition of existence as it applies to
non-presence containers and the expected behavior when one performs a "create"
or "delete" operation on them in an <edit-config>.

RFC 6020 states:

7.5.8.  NETCONF <edit-config> Operations
   ...

   If a container does not have a "presence" statement and the last
   child node is deleted, the NETCONF server MAY delete the container.
   ...

The way I read this is that the existence of non-presence containers that have
no child data, as it relates to <edit-config>, is implementation-defined.

Another place where the existence of non-presence containers is mentioned is
for the XPath context.

RFC 7950 states:

6.4.1.  XPath Context
   ...

   If a node that exists in the accessible tree has a non-presence
   container as a child, then the non-presence container also exists in
   the accessible tree.
   ...

This seems to clearly define existence for non-presence containers, which has
implications on whether the container's child "must" statements are evaluated.
However, it does not say whether existence in the XPath context is equivalent
to existence in <edit-config> operations.  As well, this passage seems to have
been introduced for YANG 1.1 and is not present in RFC 6020.

Thanks,
Gary Wu