Subject: [netmod] Fwd: Multiple deviations with same target

From: Balazs Lengyel <[email-masked]>
Date: Mon, 8 Feb 2016 12:28:20 +0100

Hello,

IMHO the case, when 2 deviation statements point at the same target
should be clarified and declared as an error or implementation
dependent feature. I see no good way of deciding which deviation
statement has precedence.

Balazs

-------- Forwarded Message --------

Subject:

[netmod] Multiple deviations with same target

Date:

Thu, 10 Dec 2015 11:12:02 +0100

From:

Balazs Lengyel <[email-masked]>

To:

[email-masked] <[email-masked]>

Hello,
What happens if I have multiple deviation statements with the same
target node, possibly in separate deviation files.
E.g it is possible to have two deviation statements setting the range
for an integer type leaf to 1..5 in one statement while setting it to
2..6 in another.
What is the end result? Error?
regards Balazs

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Mobile: +36-70-330-7909 email: [email-masked]

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---

From: Ladislav Lhotka <[email-masked]>
Date: Mon, 8 Feb 2016 13:22:18 +0100

> On 08 Feb 2016, at 12:28, Balazs Lengyel <[email-masked]> wrote:
> 
> Hello,
> IMHO the case, when 2 deviation statements point at the same target should be clarified and declared as an error or implementation dependent feature. I see no good way of deciding which deviation statement has precedence.

I think it should be an error.

Lada

> Subject:	[netmod] Multiple deviations with same target
> Date:	Thu, 10 Dec 2015 11:12:02 +0100
> From:	Balazs Lengyel <[email-masked]>
> To:	[email-masked] <[email-masked]>
> 
> Hello,

--
Ladislav Lhotka, CZ.NIC Labs
PGP Key ID: E74E8C0C

---

From: Martin Bjorklund <[email-masked]>
Date: Tue, 16 Feb 2016 09:00:33 +0100 (CET)

Hi,

Balazs Lengyel <[email-masked]> wrote:
> Hello,
> IMHO the case, when 2 deviation statements point at the same target should be
> clarified and declared as an error or implementation dependent feature. I see no
> good way of deciding which deviation statement has precedence.

This was discussed back in 2009: 
https://mailarchive.ietf.org/arch/msg/netmod/IYW1t0PX34cf2GEGAlM98XFOfKw

This thread ends w/o clear resolution, but I think that the proposal
in the last email in this thread (please read the thread) would be a
useful addition:

  After applying all deviations, in any order, the resulting data
  model MUST still be valid.  For example, it is an error to add a
  default value that doesn't match the type in a deviation.

/martin

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Tue, 16 Feb 2016 12:42:27 +0100

>   default value that doesn't match the type in a deviation.

Speaking as technical contributor:

  The second sentence is not really adding value. In the first
  sentence, it may be not entirely clear what _all_ deviations
  means. I assume this is 'all deviations announced by a server.
  So perhaps the proposal is to add

    After applying all deviations announced by a server, in any order,
    the resulting data model MUST still be valid.

  just before the beginning of section 7.20.3.1?

Speaking as co-chair and document shepherd:

  Procedurally, this comes _very_ late and I do not want to go into a
  loop where there is always one more thing to fix but then each fix
  requires several days of additional delay to determine consensus.
  So I rather have the next I-D without this change posted so that we
  can get YANG 1.1 into the hands of Benoit. If we in parallel do find
  consensus on this particular clarification, someone can submit e.g.
  an IETF last call comment to fold this in. I am sure we will get
  more comments and change requests from Benoit, the IESG, the various
  directorates etc. and I rather have this process started ASAP.

/js

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Juergen Schoenwaelder           Jacobs University Bremen gGmbH
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Fax:   +49 421 200 3103         <http://www.jacobs-university.de/>

---

From: Martin Bjorklund <[email-masked]>
Date: Tue, 16 Feb 2016 14:43:46 +0100 (CET)

>   just before the beginning of section 7.20.3.1?

Ok.

>   directorates etc. and I rather have this process started ASAP.

Ok.  I have posted -11 w/ the agreed upon changes (not the deviation
thing above).

/martin