Hi Balazs,
I think that every instance data document logically has a YANG schema
associated with it (i.e. a set of YANG modules, deviations, and enabled
features).
YANG library defines this schema on a per datastore basis, along with
other information.
My YANG packages is another attempt to construct these schema in a
hierarchical way.
Directly embedding the necessary information to facilitate a client
reading the YANG instance data also makes sense.
Please see inline ...
On 14/02/2019 10:23, Balázs Lengyel wrote:
On 2019. 02. 07. 13:10, Robert Wilton wrote:
Hi Balazs,
Regarding identifying the instance data using a YANG package.
If the YANG packages work is liked by the WG and progresses, then it
seems plausible that a YANG package could become a better way of
identifying the set of modules rather than using YANG library for a
couple of reasons:
1) It will allow modules to be identified via semantic version
rather than just revision date. This will likely be more meaningful
to readers.
BALAZS: The nice thing about using yang-library is that when the
semver work augment the library with the module-version it will be
available for instance-data for free.
RW:
This only works if the reference to the schema includes the semver
augmentation. Your current approach of
"ietf-yang-library@\d{4}-\d{2}-\d{2}\.yang';" doesn't allow this, unless
the semver work produces a new version of YANG library rather than an
augmentation.
I have no opposition to YANG library being one of the mechanisms to
construct the schema, but I think that it should also be possible to
define the schema inline, or use YANG packages (in future).
2) It allows for a much more concise definition. Rather than having
to try and infer what schema a particular set of YANG modules related
to from the list of modules, it can instead refer to a single package
definition and version number.
BALAZS: Using packages would be more, concise however in some cases
you might not want to declare a package. E.g. we use a modular
architecture where one design group might be responsible for only one
YANG module (YAM). They need to deliver some instance-data related to
that YAM, but they don't want to declare a package that contains just
one YAM. Also some modules are packaged in so many ways that it is
easier to define their instance data just for that module. So while
packages are an interesting idea they will never completely replace
the module level, hence we need a module level solution too. One
packages are agreed, I will be happy to expand this specification.
RW:
But if I understand your approach correctly then to handle this case the
instance data would need to reference a separate instance data file that
uses YANG library to define the one YANG module that is uses.
If the schema is just a single YANG module then I think that it would be
better to define that schema inline in the instance data document, and
avoid the redirection. Perhaps to keep it simple we restrict the list
of YANG modules that can be used to define to define the schema inline
to state that sub-modules cannot be used, and all features are assumed
to be enabled. If either of these conditions are not met then an
external schema definition must be used.
3) YANG library (certainly RFC7895bis) defines the schema in terms
of the datastore, so if this version of YANG library is being used
then it is a bit more confusing as to which datastore is being
referred to. I appreciate that there is a datastore leaf in the
instance data that can help mitigate this.
I also note that the draft currently binds that the only allowed
inline schema is YANG library, but that seems somewhat overly
restrictive, and perhaps this could be loosened to a leaf-list of
inline module@revision definitions?
BALAZS: IMHO ietf-yang-library contains ll the data we need in a well
defined format (and some we don't always need). So why define a new
format when we already have one. Also by using YANG library we get for
free any new data in it e.g.module-version. We also need the info
about leafs and deviations.
RW:
Because YANG library isn't really the right format, and the goal of YANG
library isn't to define this instance data file, but actually to define
the capabilities of a server.
E.g. RFC 7895bis contains the information on how to build multiple
datastore schema rather than just one. So, if 7895bis is being used to
construct a schema, then you also need to identify which datastore in
YANG library represents the schema associated with the instance data.
I also don't think that you get augmentations from free. How would a
client know which augmentations to YANG library are being used unless
that is defined somewhere?
I also appreciate that you don't want to delay the instance data
draft for YANG packages, bit I wonder whether the draft can easily
facilitate using a YANG package definition in future if required.
BALAZS: As I agree with your comment about choice (see below) that a
package reference can be easily included in that.
Hence, rather than using a union for the "target pointer", I wonder
whether it wouldn't be better to use a choice statement instead.
E.g. the choice statement could be something like this:
choice "schema"
leaf-list inline {
type string {
pattern '\w+@\d{4}-\d{2}-\d{2}\.yang';
}
}
leaf yang-library-ref { type uri } // Points to a instance data
document YANG library content.
}
In future, the package draft could then augment (or update the
revision) with something like this :
container package-ref {
leaf "name" { type string; }
leaf "version" { type yang-semver; }
leaf-list "url" { type uri; }// Points to a instance data
document containing YANG package content.
}
BALAZS: OK, choice maybe a better choice because it is easier to
extend and because it explicitly states the method used. So how about:
choice "target-specification"
leaf inline {
type string { pattern 'ietf-yang-library@\d{4}-\d{2}-\d{2}\.yang'; } //
I still want to use the library
}
leaf yang-library-ref { type uri }
}
RW:
I still think that binding "inline" to YANG library is too restrictive.
This effectively means that there is a version of instance data
documents that the only thing that they can contain is YANG library
information (without augmentation).
Thanks,
Rob
Later we can augment this choice with container package-ref.
Thanks,
Rob
On 06/12/2018 10:15, Balázs Lengyel wrote:
Hello,
We uploaded a new version of the instance data draft. We tried to
address all comments and also to rework the format chapter to make
it easier to read. We omitted 2 comments:
Rob commented that YANG packages could be used for defining the
target modules for instance data: I would like to avoid that because:
* Packages are not defined for YANG. Currently they are not part
of the versioning solution even though they were discussed and
are generally a good idea.
* IMHO as deviations/features are set on module level, just
specifying packages would not be enough. If we start using
package+module level deviations/features we may end up with a
more complicated hybrid solution.
* Module level YANG target definitions as described in the draft
are simple and need no new design
Jürgen stated that it would be better to use the YANG XML/JSON
encoding as a format instead of referencing the get
operation/request. I might even agree with him, but for 2 reasons I
did not follow his idea:
* Currently there is no RFC I could reference either for XML or
JSON. AFAIK even RFC7951 does not define how multiple modules
should be encoded side by side.
* It is not the job of the instance data draft to dictate how to
encode YANG data generally e.g. on the wire.
* The contents of the get operation/request are well defined
regards Balazs
-------- Forwarded Message --------
Subject: New Version Notification for
draft-ietf-netmod-yang-instance-file-format-01.txt
Date: Thu, 6 Dec 2018 02:12:12 -0800
From: internet-dra...@ietf.org
To: Benoit Claise <bcla...@cisco.com>, Balazs Lengyel
<balazs.leng...@ericsson.com>
A new version of I-D, draft-ietf-netmod-yang-instance-file-format-01.txt
has been successfully submitted by Balazs Lengyel and posted to the
IETF repository.
Name: draft-ietf-netmod-yang-instance-file-format
Revision: 01
Title: YANG Instance Data File Format
Document date: 2018-12-06
Group: netmod
Pages: 21
URL:
https://www.ietf.org/internet-drafts/draft-ietf-netmod-yang-instance-file-format-01.txt
Status:
https://datatracker.ietf.org/doc/draft-ietf-netmod-yang-instance-file-format/
Htmlized:
https://tools.ietf.org/html/draft-ietf-netmod-yang-instance-file-format-01
Htmlized:
https://datatracker.ietf.org/doc/html/draft-ietf-netmod-yang-instance-file-format
Diff:
https://www.ietf.org/rfcdiff?url2=draft-ietf-netmod-yang-instance-file-format-01
Abstract:
There is a need to document data defined in YANG models when a live
YANG server is not available. Data is often needed already in design
time or needed by groups that do not have a live running YANG server
available. This document specifies a standard file format for YANG
instance data, which follows the syntax and semantic from existing
YANG models, re-using existing formats from <get> operation/request
and decorates them with metadata.
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.
The IETF Secretariat
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Balazs Lengyel Ericsson Hungary Ltd.
Senior Specialist
Mobile: +36-70-330-7909 email:balazs.leng...@ericsson.com
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Balazs Lengyel Ericsson Hungary Ltd.
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Mobile: +36-70-330-7909 email:balazs.leng...@ericsson.com
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