Re: [netmod] YANG versioning requirements

[Vladimir Vassilev <[e-mail]>]

Hi Robert,

On 10/3/18 11:44 AM, Robert Wilton wrote:
>
> Hi Vladimir,
>
> At IETF 102, when I was presenting on the YANG versioning requirements 
> (draft-verdt-netmod-yang-versioning-reqs-00), I think you raised a 
> concern about requirement 2.2:
>
> 2.2 A mechanism SHOULD be defined to determine whether data nodes 
> between two arbitrary YANG module revisions have (i) not changed, (ii) 
> changed in a backward compatible way, (iii) changed in a non-backward 
> compatible way.
>
> IIRC, I think that your specific concern is that this leads to a 
> complex solution, which I understand, but I still think that this 
> requirement should remain for several reasons:
>
> (1) It is only marked as a SHOULD rather than a MUST. I.e. it is 
> desirable that a solution is able to achieve this but is not strictly 
> required.

I agree with your point in (1). As long as 2.2 is optional there is no 
problem.

>
>
> (2) Some tooling for this already exists.  RFC 7950 section 11 already 
> defines what constitutes a backwards compatible change, and pyang is 
> already capable of comparing two module revisions to partially 
> determine what non backwards compatible changes exist between two 
> module revisions
>
>
> (3) Having considered all the various potential solutions to the 
> versioning problem, my opinion is that there is only one solution that 
> is generically capable of accurately telling a client of what the 
> impact is when updating between two releases.  That solution is to 
> compare the complete schema for both releases (considering module 
> versions, deviations, and features), potentially filtering the 
> comparison output by the subset of the schema actually used by the client.
>
> So, whilst I still think a simpler solution may be helpful to 
> communicate what sort of changes are contained in a module, I still 
> think that the full complex solution will eventually be required to 
> truly solve this problem in a robust way.

My point was that the need of complete schema comparison as described in 
(3) is needed for 2.2 but not for 2.1 and thus it will probably make 
sense to decouple the solutions. I am looking forward to see what your 
solution ideas are.

>
>  Hence, are you OK with this requirement text remaining as is, or do 
> you still want to see it changed?
Yes I am OK with the text.


Regards,

Vladimir

>
>
> Thanks,
> Rob
>
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