Subject: [netmod] DSDL questions

From: Andy Bierman <[email-masked]>
Date: Fri, 23 May 2008 09:10:27 -0700

Hi,

I looked over the specs at the DSDL WEB site:
http://dsdl.org/

Q1) Of the 10 documents listed there, which subset is
     the NETMOD WG selecting?

Q2) Where can I find free tools which do useful things with
     the DSDL framework?

Q3) Where can I find data models which have already been written
     in DSDL+Schematron, so I can understand it better?  (I mean
     other than the examples generated for the benefit of the CANMOD BoF)

Andy

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From: Ladislav Lhotka <[email-masked]>
Date: Sat, 24 May 2008 00:17:47 +0200

> Q1) Of the 10 documents listed there, which subset is

In the first phase mainly parts 2 (RELAX NG) and 3 (Schematron).
> Q2) Where can I find free tools which do useful things with

The reference implementation for ISO Schematron (XSLT stylesheet) is
here: http://www.schematron.com/implementation.html
Other implementations are listed in the "Resources" and "Links" sections
at the same site.

>      other than the examples generated for the benefit of the CANMOD BoF)

AFAIK, the most comprehensive example so far is Rohan's DHCP schema in
Appendix D of draft-mahy-canmod-dsdl-01.txt. Some generic examples can
be found in this tutorial:
http://www.zvon.org/xxl/SchematronTutorial/General/toc.html

Lada

-- 
Ladislav Lhotka, CESNET
PGP Key ID: E74E8C0C

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From: Andy Bierman <[email-masked]>
Date: Fri, 23 May 2008 18:14:05 -0700

>> Q1) Of the 10 documents listed there, which subset is

The dsdl.org WEB site has not been updated since November 2006.
2 of the 10 documents were never written.  Most of them do not
look like they have much deployment.

> Other implementations are listed in the "Resources" and "Links" sections

The premise for this DSDL+Schematron charter requirement is
clearly stated in the first sentence:

    In order to leverage existing XML tools for validating NETCONF
    data in various contexts and also facilitate exchange of data
    models and schemas with other IETF working groups, the WG will
    define standard mapping rules from YANG to the DSDL data modeling
    framework (ISO/IEC 19757) with additional annotations to preserve
    semantics.

It is reasonable to expect more deployment of this RNG+Schematron
technology than a beta-level reference implementation for Schematron.

> http://www.zvon.org/xxl/SchematronTutorial/General/toc.html

These are 'Hello world' kind of models.
We need to model huge, complex stuff like DIFFSERV-MIB.

<charter-rant>
I assumed that the closed design team worked out details
such as the skilled people needed to complete each document
deliverable.  It doesn't look that way for the ISO 19757 mapping.
Never mind the obvious question of why the NETCONF WG should
be forced to used this standard when the applications world
does not even use it -- how about the practical question of
how will the WG adequately specify and review this mapping document?

It is one thing if the IESG wants to mandate that all WGs switch
from XSD to RelaxNG (or is it just the NETCONF WG again?).
I can deal with that.  There are lots of tools for RelaxNG.
(I am working on a NETCONF client lib for libxml2, even,
which has great RelaxNG support. ;-)

I think a YANG to RelaxNG mapping makes practical sense,
standards sense, and we have the resources to do a competent
job on the mapping document.  IMO, any more than that is really doubtful.
</charter-rant>

Andy

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From: Ladislav Lhotka <[email-masked]>
Date: Sat, 24 May 2008 13:51:24 +0200

> job on the mapping document.  IMO, any more than that is really

RELAX NG will certainly be the most fundamental part in any case. It
will make no harm though to express some constraints, e.g., those
specified in "must" or "unique" statements, with Schematron rules
embedded in the RELAX NG schema, and metainformation in Dublin Core.
This will be already quite useful.

You are right that the other parts of DSDL are still
researchy/vaporware. However, some of these concepts are IMO of interest
even for YANG itself. This is especially the case of the Datatyping
Library Language. This paper by Jeni Tennison gives a nice overview of
the problems of the existing libraries for XSD, RNG, and YANG as well:

http://www.idealliance.org/papers/extreme/proceedings/html/2006/Tennison01/EML2006Tennison01.html

Lada

-- 
Ladislav Lhotka, CESNET
PGP Key ID: E74E8C0C

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From: Andy Bierman <[email-masked]>
Date: Sat, 24 May 2008 09:12:26 -0700

> http://www.idealliance.org/papers/extreme/proceedings/html/2006/Tennison01/EML2006Tennison01.html

The charter says:

     In order to leverage existing XML tools

It does not say:

     In order to leverage existing XML research

I view the XSD or RNG type of mapping as the human-to-machine
translation, needed to support existing XML tools.  IMO,
XSD is good enough, but RNG is better than XSD, so it's hard
to argue against a YANG to RNG mapping.

Without tools, and some real examples from XML application
experts, I don't see how the WG (and IETF) can make practical
use of the DSDL framework.  I have concerns about a requirement
to include cryptic syntax in every NETCONF data model RFC,
which relies on one alpha-level translator implementation
and one beta-level validator implementation.  That might
be fine for research, but not for the IETF standards track.

Andy

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From: Ladislav Lhotka <[email-masked]>
Date: Mon, 26 May 2008 13:27:18 +0200

>      In order to leverage existing XML research

Right, but the charter also says: "..., the WG will
define standard mapping rules from YANG to the DSDL data modeling
framework (ISO/IEC 19757) with additional annotations to preserve
semantics."

So the first goal is to create 1:1 mapping from YANG to RELAX NG with
annotations. These annotations may be Schematron, compatibility
annotations defined as part of RELAX NG, other parts of DSDL or others
that we will have to invent. However, faced with the dilemma of choosing
either the DSDL formalism (even if no tools for it exist yet) or
inventing new annotations, I would mostly prefer the former.

This full schema will then serve as a source for various transformations
proving related schemata for concrete tasks like validation of data
stores or NETCONF PDUs (via XSLT and other existing methods). It is this
"application part" where the existing XML tools will be leveraged.

Lada

-- 
Ladislav Lhotka, CESNET
PGP Key ID: E74E8C0C