Re: [netmod] choice/case in tree diagrams

Martin Bjorklund <mbj@tail-f.com> Mon, 05 March 2018 14:26 UTC

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Date: Mon, 05 Mar 2018 15:26:02 +0100 (CET)
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From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] choice/case in tree diagrams
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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


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'.)