Hello friends,
I have got some puzzles about YANG model design, to be more specific, it is
about the identifier design in YANG model.
As we know, YANG model is a tree-like structure, different objects are defined
in different branches according their different levels. E.G. there is such a
YANG tree:
module: ietf-example
+--rw root
+--rw list-a* [leaf-1]
+--rw leaf-1 yang:uuid
+--rw leaf-2? string
+--rw list-b* [leaf-3]
+--rw leaf-3 yang:uuid
+--rw leaf-4? string
+--rw list-c* [leaf-5]
+--rw leaf-5 yang:uuid
+--rw leaf-6? string
List-c is child object of list-b and list-b is child object of list-a.
If we want to retrieve a list-c instance, we need to know his parent list-b's
and his grandparent list-a's identifier to construct a RESTCONF GET request URL:
https://{{host:port}}/{{restconf}}/data/ietf-example:root/list-a={leaf-1}/list-b={leaf-3}/list-c={leaf-5}.
However, you can easily find that the identifier of list-a, list-b and list-c
are all UUID format. Usually, UUID is required to be unique globally. If the
RESTCONF server complies with UUID requirement strictly, the identifier of
list-b and list-a are redundant.
Similarly, if there is a YANG data model want to reference list-c in its model,
the reference identifier should include list-b and list-a's identifier at the
same time besides list-c's identifier. If this list-c instance repeat a lot of
time in this data model, there would be a lot of redundant list-b & list-a's
identifier.
Besides, this hierarchical identifier brings some problems when we are
designing generic model. For example, if we want to design an alarm model,
considering that the main information of alarm includes alarm ID, alarm level,
tips message, location etc. which are generic for all inventory objects, it is
easy for us to choose to design a generic model. For the inventory object alarm
happened on, we would like to use a generic inventory resource type and
resource UUID to specify. But if we use hierarchical identifier, considering
alarm could be happened on NE, board or port .etc. and NE contains boards and
board contains ports, we cannot use a generic identifier attribute to specify
NE, board and port at the same time. For NE, we need to use one attribute to
define its ne-id. And for board we need two attributes to define its id, ne-id
and board-id. And for port, we need three attributes to define its id, ne-id,
board-id and port-id.
So I am wondering if for those objects which are using UUID as identifier, the
server should implement this UUID globally unique. When retrieving these
objects, there is no necessary to specify their parent's and grandparent's
identifier. Just take the list-c retrieval above for example, the URL could be
changed to be:
https://{{host:port}}/{{restconf}}/data/ietf-example:root/list-a/list-b/list-c={leaf-5}<https://%7b%7bhost:port%7d%7d/%7b%7brestconf%7d%7d/data/ietf-example:root/list-a/list-b/list-c=%7bleaf-5%7d>.
And for model object reference scenario, we can also use list-c's identifier
only.
This is just my consideration, any comments are welcome! Thank you!
B.R.
Chaode
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