Re: [netmod] I-D Action: draft-ietf-netmod-yang-data-ext-01.txt
Andy Bierman <andy@yumaworks.com> Sat, 20 October 2018 15:16 UTC
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From: Andy Bierman <andy@yumaworks.com>
Date: Sat, 20 Oct 2018 08:15:58 -0700
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To: Robert Varga <nite@hq.sk>
Cc: NetMod WG <netmod@ietf.org>
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Subject: Re: [netmod] I-D Action: draft-ietf-netmod-yang-data-ext-01.txt
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On Mon, Oct 15, 2018 at 1:28 PM, Robert Varga <nite@hq.sk> wrote: > On 06/03/2018 00:56, internet-drafts@ietf.org wrote: > > A New Internet-Draft is available from the on-line Internet-Drafts > directories. > > This draft is a work item of the Network Modeling WG of the IETF. > > > > Title : YANG Data Extensions > > Authors : Andy Bierman > > Martin Bjorklund > > Kent Watsen > > Filename : draft-ietf-netmod-yang-data-ext-01.txt > > Pages : 11 > > Date : 2018-03-05 > > > > Abstract: > > This document describes YANG mechanisms for defining abstract data > > structures with YANG. It is intended to replace and extend the > > "yang-data" extension statement defined in RFC 8040. > > Sorry to be a late reviewer on this. > > To me "augment-yang-data" feels really like "augment a particular > instance of a schema tree", i.e. increasing specificity of augment > target node with knowledge on which tree instantiation it operates. > > RFC7950 already does this (implicitly) for notification, rpc and action > statements by making them members of the schema tree and the same > "augment" and "deviation" mechanics for them being defined shared with > the data tree. > > I would argue this problem from a different point of view. > > I think the purpose of "augment-yang-data" would be much better > addressed with an extension usable within augment (and deviate) to > reference a particular schema tree instantiation. > > I do not agree that the scope of this work should be expanded. If there are specific language features that need to be standardized, then a new version of YANG should be standardized instead. Andy What that means in terms of YANG metamodel is two-fold: > > 1) an extension statement can define a conceptual schema tree > instantiation -- very much like NMDA does, but applied not to datastore, > but to schema tree. > > 2) an augment (or deviation) statement can be restricted to operate on a > schema tree instantiation defined by an extension statement > > Rough example: > > extension augmentable-statement; > extension schematree-instance; > > extension yang-data { > as:augmentable-statement; > } > > yd:yang-data foo; > > augment /foo { > // i.e. interpret argument as a target valid in the schema tree > // as defined by yang-data, with the semantics specified therein > si:schematree-instance "yd:yang-data"; > } > > Note how as:schematree-instance is completely unnecessary here: > yang-data's use of as:augmentable-statement is already indicating that > the statement is augmentable, thus bridging it to RFC7950 section 7.19: > > An extension can allow refinement (see Section 7.13.2) and deviations > (Section 7.20.3.2), but the mechanism for how this is defined is > outside the scope of this specification. > > hence the only extension that is needed for yang-data and future similar > extensions is augmentable-statement, simply because as soon as "augment" > argument touches an extension statement, you have to know something > about it. If an augment argument crosses an extension statement, it must > share fate with the parser's handling of the extension: if the parser > chooses to ignore the extension, it should reasonably also ignore the > augment statement. > > Unless "augment" is not allowed to touch extension statements (i.e. > extensions must never define a schema tree member) -- if that is the > case, that should be normatively defined somewhere, too. > > Regards, > Robert > > > _______________________________________________ > netmod mailing list > netmod@ietf.org > https://www.ietf.org/mailman/listinfo/netmod > >
- [netmod] I-D Action: draft-ietf-netmod-yang-data-… internet-drafts
- Re: [netmod] I-D Action: draft-ietf-netmod-yang-d… Robert Varga
- Re: [netmod] I-D Action: draft-ietf-netmod-yang-d… Andy Bierman