Re: [netmod] I-D Action: draft-ietf-netmod-yang-data-ext-01.txt
On Mon, Oct 15, 2018 at 1:28 PM, Robert Varga wrote:
> On 06/03/2018 00:56, internet-dra...@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
>
>
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>
>
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Re: [netmod] I-D Action: draft-ietf-netmod-yang-data-ext-01.txt
On 06/03/2018 00:56, internet-dra...@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.
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
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[netmod] I-D Action: draft-ietf-netmod-yang-data-ext-01.txt
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. The IETF datatracker status page for this draft is: https://datatracker.ietf.org/doc/draft-ietf-netmod-yang-data-ext/ There are also htmlized versions available at: https://tools.ietf.org/html/draft-ietf-netmod-yang-data-ext-01 https://datatracker.ietf.org/doc/html/draft-ietf-netmod-yang-data-ext-01 A diff from the previous version is available at: https://www.ietf.org/rfcdiff?url2=draft-ietf-netmod-yang-data-ext-01 Please note that it may take a couple of minutes from the time of submission until the htmlized version and diff are available at tools.ietf.org. Internet-Drafts are also available by anonymous FTP at: ftp://ftp.ietf.org/internet-drafts/ ___ netmod mailing list netmod@ietf.org https://www.ietf.org/mailman/listinfo/netmod
