Re: [netmod] choice/case in tree diagrams

Per Hedeland <per@tail-f.com> Mon, 05 March 2018 14:49 UTC

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From: Per Hedeland <per@tail-f.com>
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Subject: Re: [netmod] choice/case in tree diagrams
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On 2018-03-05 15:41, Ladislav Lhotka wrote:
> On Mon, 2018-03-05 at 15:26 +0100, Martin Bjorklund wrote:
>> Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
>>> On Mon, Mar 05, 2018 at 02:54:18PM +0100, Martin Bjorklund wrote:
>>>>>
>>>>> So it seems the running code got it right. ;-)
>>>>
>>>> As the author of that code, I think that was purely by accident...
>>>>
>>>> But I'm not convinced it is the correct solution.  We have one example
>>>> in the other thread where someone was confused by the "rw" flag and
>>>> thought that it implied that the node would be present in the data
>>>> tree.
>>>>
>>>
>>> So what does rw mean?
>>>
>>> (i)  The schema node has a rw property.
>>> (ii) The schema node can be instantiated and the instantiated data node
>>>      has a rw property.
>>>
>>> I think it is difficult to have both at the same time. If the tree is
>>> a representation of schema nodes, then (i) seems to make more
>>> sense. That said, the explanation in 2.6 is somewhat vague since it
>>> says 'data' and not 'nodes' (like everywhere else):
>>>
>>> OLD:
>>>
>>>        <flags> is one of:
>>>          rw  for configuration data
>>>          ro  for non-configuration data, output parameters to rpcs
>>>              and actions, and notification parameters
>>>
>>> NEW:
>>>
>>>        <flags> is one of:
>>>          rw  for configuration data nodes
>>>          ro  for non-configuration data nodes, output parameters to rpcs
>>>              and actions, and notification parameters
>>
>> I think this is ok.  But that means that we also have to add:
>>
>>            --  for a choice or case node
>>
>> But in order to be consistent, we should probably have:
>>
>>            --  for a choice, case, input or output node
> 
> But unlike the three other statements, "choice" can have the config
> substatement, so "rw/ro" makes sense there.

I don't think so - that config statement does not a define a property of
the choice node (it can obviously neither be read nor written), only a
default for descendant data nodes, as described in section 7.21.1 of RFC
7950.

--Per

> Lada
> 
>>
>>
>> This means that the correct tree syntax for choice and case will be:
>>
>>      +-- (subnet)?
>>         +-- :(prefix-length)
>>         |  +--rw prefix-length?   uint8
>>         +-- :(netmask)
>>            +--rw netmask?         yang:dotted-quad
>>
>>
>> /martin
>>
>>
>>> The document (as far as I searched for it) does not clearly say that
>>> 'node' means 'schema node'. In hindsight, it might have been useful to
>>> explicitely import terminology from RFC 7950 and to use it carefully
>>> (RFC 7950 has 'schema node' and 'data node' but here we largely talk
>>> about 'nodes' - and my assumption is that this means 'schema nodes'.)
>>
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