Re: [netmod] choice/case in tree diagrams

Mahesh Jethanandani <mjethanandani@gmail.com> Mon, 05 March 2018 18:23 UTC

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From: Mahesh Jethanandani <mjethanandani@gmail.com>
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Date: Mon, 5 Mar 2018 10:23:14 -0800
In-Reply-To: <20180305.152754.1045464928563003353.mbj@tail-f.com>
Cc: Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>, netmod@ietf.org
To: Martin Bjorklund <mbj@tail-f.com>
References: <20180305.145418.2010818875235650756.mbj@tail-f.com> <20180305141355.gi6kfej3eifdxtjq@elstar.local> <20180305.152602.113020152789243398.mbj@tail-f.com> <20180305.152754.1045464928563003353.mbj@tail-f.com>
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Subject: Re: [netmod] choice/case in tree diagrams
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> On Mar 5, 2018, at 6:27 AM, Martin Bjorklund <mbj@tail-f.com> wrote:
> 
> Martin Bjorklund <mbj@tail-f.com <mailto:mbj@tail-f.com>> 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
> 
> Whoops, it shouldn't be "--".  Somehow we should say that no flags are
> used for choice,case,input,output.

I would agree, as having choice/case statements represented as schema nodes is not only confusing in the tree diagram, but also confusing when constructing an example. The tree diagram represents it as a node, where one would put it in the example, but validation complained about it (not being a node).

> 
> 
> /martin
> 
> 
>> 
>> 
>> 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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> 
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Mahesh Jethanandani
mjethanandani@gmail.com