Re: [core] Comments on draft-ietf-core-yang-cbor-06

Hi Carsten

CoMI for example, uses delta for the first root data node based on the requested SID.
In the following example, the +2 is relative to SID 1721 which is part of the requested URI (i.e. a5).
This requested SID need to be maintained in the client state in order to process the response.

https://tools.ietf.org/html/draft-ietf-core-comi-03#section-5.2.3.1

   REQ: GET example.com/c/a5

   RES: 2.05 Content (Content-Format: application/yang-value+cbor)
   {
     +2 : "2014-10-26T12:16:51Z",   / current-datetime SID 1723 /
     +1 : "2014-10-21T03:00:00Z"    / boot-datetime SID 1722 /
   }

Regards,
Michel

-----Original Message-----
From: Carsten Bormann [mailto:cabo@tzi.org] 
Sent: Monday, July 9, 2018 11:23 AM
To: Michel Veillette <Michel.Veillette@trilliant.com>
Cc: Robert Wilton <rwilton@cisco.com>; draft-ietf-core-yang-cbor@ietf.org; core@ietf.org
Subject: Re: [core] Comments on draft-ietf-core-yang-cbor-06

It is much less confusing to always talk of deltas in the structure.

Just say that the context SID value (the one that the delta is computed from) is 0 at the root of a tree.

Grüße, Carsten

> On Jul 9, 2018, at 17:18, Michel Veillette <Michel.Veillette@trilliant.com> wrote:
> 
> Hi Robert
>  
> Andy also asked for a clarification about the encoding of the root data node identifier (absolute vs. delta).
> Section 4.4.1. have a sentence addressing this topic.
>    It is important to note that the protocol or method
>    using this mapping may carry a parent SID or may have the knowledge
>    of this parent SID based on its context.  In these cases, delta
>    encoding can be performed based on this parent SID which minimizes
>    the size of the encoded data.
>  
> A similar sentence need to be added to section 4.2.1.
> We also need to clarify that the protocol or method using this encoding must mandate which approach is implemented, the data serialized don’t carry this information.
>  
> Regards,
> Michel
>  
> From: Robert Wilton [mailto:rwilton@cisco.com] 
> Sent: Monday, July 9, 2018 11:00 AM
> To: draft-ietf-core-yang-cbor@ietf.org; core@ietf.org
> Subject: Comments on draft-ietf-core-yang-cbor-06
>  
> Hi,
> 
> I've read this draft, and think that it is well written.
> 
> There is one area of the draft that is somewhat unclear to me when using SID encodings:  Is the root node(s) of a request or a response always an absolute SID value, or could it still be a delta?
> 
> In particular:
> 
> Sec 2.1 indicates that the translation to/from SID deltas is stateless, which implies to me that the root node(s) of a request/response would always be an absolute SID value.
> 
> Sec 4.2.1 gives an example using a absolute SID for the top node.  It then has this text: "
> 
>    On the other hand, if the serializer is aware of the parent SID, 1716
>    in the case 'system-state' container, root data nodes are encoded
>    using deltas.
> "
> I think that it is quite plausible that the serializer may know the SIDs for all nodes in the data tree, which the text implies it could then use a relative SID for the top node.  Particularly, if the top level node was explicit from the request.
> 
> Hence, I think that this draft could probably benefit in being more explicit on exactly when a top level node uses an absolute SID, and in what scenarios it may end up using a a relative SID.  If this distinction is down to the protocol being used, then perhaps that could be stated?
> 
> One other nit:
> 
> Section 4.4.1 says "delta encoding can be performed", but I think that this should probably be "delta encoding MUST be performed".
> 
> Thanks,
> Rob
>  
> 
>  
> 
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