[yang-tooling] Re: SID file issues / .sid file differences in pyang and core-wg/pyang

[Esko Dijk <[e-mail]>]

Hi Carsten,

I thought "YANG item" is defined in RFC 9254 Section 2:

item:
     A schema node, an identity, a module, or a feature defined using 
the YANG modeling language.

So this would include the choice/case schema nodes.

Or is there a difference between "YANG item" and "item" ? -- in which 
case I'm officially lost. Interestingly RFC 7950 doesn't define "YANG 
item" but still uses the term.


If it was not intended to assign a SID to each "item", but rather only 
to a subset of items i.e. the ones listed in Section 3.2 of RFC 9254, I 
can understand that.
If we assign to all "items" then we get quite some SID values that 
aren't used in practice, in an actual data tree serialization in CBOR. 
This sounds less useful for a majority of use cases.

If we assume that SIDs only assigned to a subset of items is the 
intention of RFC 9595, this this text and maybe 9254 would need fixing I 
believe.

Can you confirm that YANG item is the same as "item" in RFC 9254, or 
otherwise give some hints about their (intended) difference?

Esko


On 2/4/26 13:33, Carsten Bormann wrote:
> On Feb 4, 2026, at 13:07, Esko Dijk <esko.dijk=[e-mail]> wrote:
>> assign a SID value to each "YANG item”
> Now what *is* a YANG item?
>
> The observation that the YANG terminology is less usable than we thought came relatively late in the processing of YANG-CBOR (RFC 9254), so you’ll have to excuse us not properly defining that term.
>
> Section 3.2/3.3 of RFC 9254 seem to provide the best definition.
>
> 3.2 lists the items we want SIDs to be useful for.
> Note the absence of choice/case.
>
> 3.3 describes the naming of YANG items as text strings, which are the same ones that would occur in “.sid” files.
> This section closely relates these text strings to the ones used in YANG-JSON (RFC 7951).
> (The terms “choice” and “case” do not occur in the YANG schema node sense in RFC 7951, which is probably why they don’t occur much in RFC 9254 either.)
>
> RFC 9254 is pretty much silent about “choice” and “case”.
> The one occurrence of “choice” in the RFC, Section 4.4, comes with a YANG-CBOR instance which appears to ignore the presence of choice and case schema nodes.
>
> RFC 7950 (YANG/YANG-XML):
> 7.9: A choice node does not exist in the data tree.
> 9.13: It [instance identifier] is used to uniquely identify a node in the data tree.
>
> The main purpose of SIDs/YANG item names is to build instance identifiers; this may have shaped my interpretation of how the strings that serve as YANG item names should be constructed.
>
> Grüße, Carsten
>