[netmod] Y34: use cases for anydata

[Andy Bierman <[e-mail]>]

Hi,

Sometimes it helps to agree on the actual problems that
need to be solved, before we endlessly debate solutions.
I can only think of 4 use case classes for anydata.


Use case 1: root
-----------------------
Description: The anydata node MUST be a container (JSON object)
and the child nodes MUST be top-level YANG data nodes
supported by the server (i.e., TL-nodes defined in the YANG modules
advertised by the server)

Context: rpc/input and rpc/output

Examples: edit-config <config> node, get-config <data> node


Use case 2: fixed unknown schema node
-------------------------------------------------------
Description: The anydata node MUST be a container (JSON object)
and the child nodes MUST be instances of a specific YANG.
data-def-stmt, which does not have to be a TL-node.
The specific YANG object is not known to the server.

Context: data-model dependent; could be abstract data structure,
notification, operational data

Examples: A pass-through application such as a logger


Use case 3: fixed known schema node
-----------------------------------------------------
Description: The anydata node MUST be a container (JSON object)
and the child nodes MUST be instances of a specific YANG.
data-def-stmt, which does not have to be a TL-node.
The specific YANG object is known to the server
in some ad-hoc out-of-band manner.  No machine-readable
base YANG statements indicate the actual schema node.

Context: data-model dependent; could be abstract data structure,
notification, operational data

Examples: YANG Mount


Use case 4: dynamic schema node
-------------------------------------------------
Description: The anydata node MUST be a container (JSON object)
and the child nodes MUST be instances of any YANG.
data-def-stmt, which does not have to be a TL-node.
The specific YANG object may be known to the server
in some ad-hoc out-of-band manner.  No machine-readable
base YANG statements indicate the actual schema node.

Context: rpc/input, rpc/output, ???

Examples: YANG Patch


Summary
--------------
In each case, it should be OK to encode simple nodes as strings
and complex nodes as containers. The end consumer that is
expected to know the correct schema can convert from the
string to the correct YANG type.  There are corner cases
such as instance-identifier and QNames (e.g., identityref),
but I think these can also be handled correctly if specified
in the netmod-yang-json (and metadata) drafts in enough detail.



Andy