Re: [netmod] yang-data-ext issues

[Robert Varga <[e-mail]>]

On 22/04/18 14:56, Ladislav Lhotka wrote:
>> One example: YANG 1.1 was supposed to be a backwards-compatible, yet it
>> introduced multiple-inheritence to a language which was previously
>> strictly single-inheritence. That sort of change is a major revision of
>> the metamodel and certainly does not qualify as backwards-compatible at
>> that level of abstraction.
> I'd defend YANG 1.1 here, I think it was a well managed and conservative update.
> The meaning of backward compatibility was defined in the charter: YANG 1.0
> modules should continue to work in 1.1. Apart from fixing evident bugs, I
> believe this goal was achieved.

I agree and the upgrade process was very smooth, all things considered.

> I am much more concerned with some of the post-1.1 features, also because YANG
> is now being updated in several directions without a clear vision. And another
> big problem is that YANG extensions are used for these changes, so we will
> probably end up with several different versions of YANG, although formally
> everything will be 1.1.  

Agree, and it's especially the interactions between extensions which are
critical to manage the outcome.

> Regarding your example: from my own experience, implementing validation of
> identityref values with multiple inheritance is not terribly complicated in
> comparison to single inheritance. I have other favorites for the most peculiar
> feature in YANG.

It's not, but it forced us to incompatibly change our Java binding
specifications -- where we used to use abstract classes we have to use
interfaces. Luckily there is no state involved :)

Regards,
Robert