Re: [netmod] choice/case in tree diagrams

On Mon, 2018-03-05 at 15:49 +0100, Per Hedeland wrote:
> 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.

It is not a default - if a choice has "config false", then no descendant can be
"config true". One of the benefits of having rw/ro in the ascii tree is to see
where a state data subtree actually starts.

Lada

> 
> --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'.)
> > > 
> > > _______________________________________________
> > > netmod mailing list
> > > netmod@ietf.org
> > > https://www.ietf.org/mailman/listinfo/netmod
> 
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-- 
Ladislav Lhotka
Head, CZ.NIC Labs
PGP Key ID: 0xB8F92B08A9F76C67