Re: [netmod] Fwd: New Version Notification for draft-lengyel-netmod-yang-instance-data-01.txt

Robert Wilton <> Tue, 26 June 2018 14:07 UTC

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To: Balazs Lengyel <>, "" <>
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From: Robert Wilton <>
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Date: Tue, 26 Jun 2018 15:07:16 +0100
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Subject: Re: [netmod] Fwd: New Version Notification for draft-lengyel-netmod-yang-instance-data-01.txt
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On 26/06/2018 14:52, Juergen Schoenwaelder wrote:
> On Tue, Jun 26, 2018 at 02:37:21PM +0100, Robert Wilton wrote:
>> On 26/06/2018 13:11, Juergen Schoenwaelder wrote:
>>> On Tue, Jun 26, 2018 at 01:58:44PM +0200, Balazs Lengyel wrote:
>>>>      Thanks for the comments and support. See answers below.
>>>>      Balazs
>>>>      On 6/13/2018 4:40 PM, Robert Wilton wrote:
>>>>        Hi,
>>>>        I would support this draft (if/when a call for adoption is made).
>>>>        A few comments from a quick review :
>>>>        1) I think that it would be useful to allow a file to contain multiple
>>>>        "instance data sets".  I could easily imagine that multiple different
>>>>        blocks of instance data may need to be provided and allowing these to be
>>>>        carried within a single file seems helpful.
>>>>      BALAZS: We allow multiple YANG modules in a file, but I have never seen it
>>>>      used. Actually my model/tool designers asked me to prohibit multiple YANG
>>>>      modules (YAMs) in one file at least within Ericsson. So if the group
>>>>      decides so it can be allowed, however I think it is not a good idea.
>>> What exactly is "multiple YANG modules in a file"? I am confused and
>>> you may be talking past each other.
>> An example could be wanting to provide a single file that holds the
>> capabilities for all different linecard types for a particular type of
>> device, rather than providing them as a set of files.
>> Of course, this could also be achieved using a meta YANG module (e.g. the
>> top level module could have a list of linecard types, which each linecard
>> type contains the capabilities for that linecard).  Whether this make sense
>> probably depends on the underlying YANG modules and how they are
>> constructed.
>> Of just using separate files, in which case the meta information can just be
>> managed into the file name, and the file can be provided as a zip.
> I am left puzzled. There is instance data (in a datastore) and you
> serialize (perhaps filtered) the instance data into a file. Instance
> data in general has data that conforms to multiple YANG modules, in
> particular also due to augments. I think we need to solve the general
> problem, not an isolated linecard problem.
OK, so I wasn't assuming that instance data necessarily corresponds to 
instance data coming from a datastore (or an entire datastore). I was 
thinking that it can be any data that has a well defined YANG schema 
associated with it.  E.g. perhaps it could use to represent the YANG 
data sent or received in a YANG encoded RPC.

>>     Instance data MUST follow the XML and JSON encoding rules defined in
>>     RFC7950 and 7951.  Data MUST be present in canonical form or where that is
>>     not defined in lexical representation.  Whitespace must also be handled as
>>     defined by the encoding rules.
> I thought the 2nd and 3rd sentence would be not needed but checking
> RFC 7951 I see no mentioning that values must be in canonical format.
> I guess this is an omission of RFC 7951 - perhaps I should open an
> errata. RFC 7950 says this clearly in section 9.1:
>     When a server sends XML-encoded data, it MUST use the canonical form
>     defined in this section.
> Looks like an omission in RFC 7951.
>>>>        7) It might want to include a semantic version number for an
>>>>        instance-data-set, depending on whether the YANG versioning discussions
>>>>        ends up.
>>>>      BALAZS: Yes I would like to. However I am not exactly clear on what does
>>>>      backwards compatibility mean for instance data.
>>>>      Data MAY NOT be removed or changed only added.  ???
>>>>      Who would use the semver numbers ???
>>> What does the version number mean? Every change of instance data in an
>>> instacne-data-set leads to a new version number? What is a bug fix in
>>> this sense? What is a non-backwards compatible change of instance data?
>>> I am left a bit puzzled.
>> Probably I don't mean semantic version.  But often files have versioning, or
>> revision, information associated with them.  This can be muxed into the file
>> name/path, but it also seems like potentially useful metadata, and being
>> able to handle this generically in a consistent way might be beneficial.
>> As an example, perhaps the capability information related to S/W release
>> 1.2.4, etc.
> We need to separate a version number of the instance data from the a
> version number (or version context) that may be needed in order to
> understand what a YANG (module, path) tuple means if we move to a
> different YANG versioning scheme. The later I agree would be needed,
> the former I am less sure of - at least if we talk semantic version
> numbers.
Yes, I agree with the need for the latter, that may entail listing the 
versions of the modules in the meta-data.

But what I was actually referring to was the former, and thinking more 
of it is just being a string field in the meta-data with a well defined 
name, that is optional to populate.  Actually, I see the current 
definition already has a revision with a date and description string.  
This is roughly along the lines of what I was thinking of for versioning 
(although I'm not sure why this should be a list rather than just a pair 
of leaves).


> /js