Re: [netmod] compact versus iterative representation of the overall schema

[Ladislav Lhotka <[e-mail]>]

> On 24 May 2016, at 14:52, Martin Bjorklund <[e-mail]> wrote:
> 
> Ladislav Lhotka <[e-mail]> wrote:
>> Martin Bjorklund <[e-mail]> writes:
>> 
>>> Ladislav Lhotka <[e-mail]> wrote:
>>>> 
>>>>> On 23 May 2016, at 14:30, Lou Berger <[e-mail]> wrote:
>>>>> 
>>>>> Hi Lada,
>>>>>   I looks like no one really jumped on this one -- so better late than
>>>>> never ...
>>>>> 
>>>>> When looking at the question below, we should consider the uses cases.
>>>>> I'm particularity interested (as a contributor) in the use case of
>>>>> nested mounts (NIs mounted within LNEs), as well as the case if models
>>>>> that will only permit mounting of specific other models vs generically
>>>>> mounting any model.
>>>>> 
>>>>> On 4/6/2016 10:07 AM, Ladislav Lhotka wrote:
>>>>>> Hi,
>>>>>> 
>>>>>> with a schema mount mechanism in place, there are two different
>>>>>> options
>>>>>> for constructing the overall schema (their combinations are possible,
>>>>>> too):
>>>>>> 
>>>>>> 1. Define schema mount as an extension of YANG library so that it
>>>>>> defines YANG modules, revisions, features and deviations as before but
>>>>>> also the way how they are combined into a hierarchical structure of
>>>>>> schemas.
>>>>> 
>>>>> I think this only makes sense if this is scoped in some way.  For
>>>>> example, with LNEs, the parent/host server may not have visibility
>>>>> into
>>>>> the mounted models, (see draft-rtgyangdt-rtgwg-lne-model).  And even
>>>>> if
>>>> 
>>>> As I understand it, schema-mount is about accessing the LNE models
>>>> from the parent/host management interface. I believe the real question
>>>> is whether we want to allow the schema to dynamically change at run
>>>> time and possibly throw in new modules that the client never heard
>>>> of. #2 can do it while #1 can't. I am not sure though whether the LNE
>>>> model really requires something like this.
>>>> 
>>>>> does, you have to consider the cases of mounted models contained
>>>>> within
>>>>> mounted models.
>>>> 
>>>> This is possible either way, provided that the complete schema is
>>>> known upfront.
>>> 
>>> I don't think I have seen a concrete proposal for such a compact
>> 
>> YSDL was such a proposal.
>> 
>>> format that can handle the case where different instances of a list
>>> with a mount point have different modules mounted, and some of them
>>> have mounted models within the mounted models.
>>> 
>>> As a concrete example, suppose we have the model
>>> example-network-manager from Appendix B in
>>> draft-ietf-netmod-schema-mount-01:
>>> 
>>>   +--rw managed-devices
>>>      +--rw device* [name]
>>>         +--rw name         string
>>>         +--rw transport
>>>         +--rw root      yangmnt:mount-point managed-device
>>> 
>>> Now, let's assume that two devices exist, A and B:
>>> 
>>>  A  implements:  ietf-interfaces, example-netowrk-manager
>>>  B  implements:  ietf-system
>>> 
>>> In A, there is a managed-device C which implements ietf-interfaces and
>>> ietf-ip.
>>> 
>>> What would this look like in the compact form?
>> 
>> The module "example-network-manager" would be modified as follows:
>> 
>>   +--rw managed-devices
>>      +--rw device* [name]
>>         +--rw name         string
>>         +--rw transport
>>         +--rw (root)
>>            +--:(A)
>>            +--:(B)
>>            +--:(C)
> 
> But A, B and C are device names (instances).

So what? A, B and C can be the values of the "name" key, too.

> 
> Also, C would be:
> 
>  /managed-devices/device[name="A"]/root/managed-devices/device[name="C"]

Yes.

> 
> 
>> And then:
>> 
>>   {
>>     "ietf-ysdl:schemas": {
>>       "top-schema": "host",
>>       "schema": [
>>         {
>>           "name": "host",
>>           "yang-modules": [ "example-logical-devices" ],
>>           "subschema": [
>>             {
>>               "root":
>>                 "/example-network-manager:managed-devices/device/root/A",
> 
> Can the root contain instance information?

No, it is a schema-node-path, that's why it can contain "choice" and "case" nodes. It should be possible to construct the complete schema without looking into any instances.

Lada

> 
> 
> /martin
> 
> 
>>               "schemas": [ "schema-A" ]
>>             }
>>             {
>>               "root":
>>                 "/example-network-manager:managed-devices/device/root/B",
>>               "schemas": [ "schema-B" ]
>>             }
>>           ]
>>         },
>>         {
>>           "name": "schema-A",
>>           "yang-modules": [
>>             "ietf-interfaces",
>>             "example-network-manager"
>>           ],
>>           "subschema": [
>>             {
>>               "root":
>>                 "/example-network-manager:managed-devices/device/root/C",
>>               "schemas": [ "schema-C" ]
>>             }
>>           ]
>>         },
>>         {
>>           "name": "schema-B",
>>           "yang-modules": [ "ietf-system" ]
>>         },
>>         {
>>           "name": "schema-C",
>>           "yang-modules": [
>>             "ietf-interfaces",
>>             "ietf-ip"
>>           ]
>>         }
>>       ]
>>     }
>>   }
>> 
>> As long as all modules comprising the schema and their possible
>> arrangement is known in advance, it should flexible enough. And as I
>> said, I'd prefer to address this case in schema-mount because the model
>> of trust between the server and client isn't changed in any way.
>> 
>>> 
>>> BTW, in this case, it is not obvious that the top-level server knows
>>> anything about the data models mounted by C...
>> 
>> But then the top-level server cannot possibly serve data for C.
>> 
>> Lada
>> 
>>> 
>>> 
>>> /martin
>>> 
>>> 
>>> 
>>> 
>>>> 
>>>>> 
>>>>>> 
>>>>>> 2. Apart from YANG Library data, the server just specifies the mount
>>>>>> points. A client of an NM protocol is expected to fetch a new instance
>>>>>> of YANG library and/or subordinate mount points as state data from a
>>>>>> well-known location under each mount point.
>>>>> 
>>>>> I think this depends on the use case.  For LNEs, I think this is
>>>>> right.
>>>>> For some of the other possible use cases being discussed only a
>>>>> specific
>>>>> model can be mounted.
>>>> 
>>>> I guess I need some example scenarios demonstrating that #1 cannot be
>>>> used for LNE.
>>> 
>> 
>> -- 
>> Ladislav Lhotka, CZ.NIC Labs
>> PGP Key ID: E74E8C0C
>> 

--
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C