Subject: Re: [netmod] draft-rabil-dhc-dhcpv6-xmlconfig-00.txt

From: "A. Gregory Rabil" <[email-masked]>
Date: Tue, 26 May 2009 12:56:48 -0400

Hello NETCONF/NETMOD gurus,

I have made an individual submission of an Internet-Draft which describes an
XML schema for configuration of DHCPv6 servers.

http://www.ietf.org/internet-drafts/draft-rabil-dhc-dhcpv6-xmlconfig-00.txt

However, you will note that the definition is in XML Schema syntax.  I have
read the YANG draft, as well as a related draft which describes converting
from YANG *to* XML schema.  In general, I have to admit that I'm having
trouble understanding the need for *another* language for specifying the
contents of XML.  XML Schema was supposed to be the defacto standard, now
RelaxNG is competing for that, and further we have YANG.  I would like to
receive any comments or feedback from the folks in this working group as to
what mechanisms may exist for converting *from* XML Schema *to* YANG or
suggestions for defining the schema just once without the need to maintain
several "authoritative" sources of the schema definition.

BTW, an open-source implementation of a stateless DHCPv6 server which uses
the XML configuration schema defined in the above draft as its native
configuration format, is available at:

http://code.google.com/p/jagornet-dhcpv6

Best regards,
Greg Rabil

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From: Martin Bjorklund <[email-masked]>
Date: Tue, 26 May 2009 21:39:04 +0200 (CEST)

Hi Greg,

"A. Gregory Rabil" <[email-masked]> wrote:
> In general, I have to admit that I'm having
> contents of XML.

YANG is not a generic XML Schema language.  It is not used to specify
the syntax of generic XML instance documents.

YANG is used to describe configuration data models that can co-exist
with other data models, evolve over time, be extended by other data
models, and that can be manipulated with the NETCONF protocol.

YANG is also used to decribe state data, rpcs and notifications, all
handled by NETCONF.

Some info is available at
http://www.yang-central.org/twiki/bin/view/Main/WhyYang and from other
links at yang-central.

> XML Schema was supposed to be the defacto standard, now
> what mechanisms may exist for converting *from* XML Schema *to* YANG

This is not possible in the general case, since YANG cannot model
e.g. XML attributes.

> or

If you have a YANG model, you can generate XSD and RNG from that
model.  This is implemented in tools like pyang and yangdump.

/martin

---

From: "A. Gregory Rabil" <[email-masked]>
Date: Tue, 26 May 2009 16:58:57 -0400

Hi Martin,

Thank you for your response.  The "WhyYang" page really clears some things
up for me.  I would consider converting my draft to one that uses YANG, if
you believe that there would be interest from the NETCONF/NETMOD community
for me to do so.

Regards,
Greg

---

From: Martin Bjorklund <[email-masked]>
Date: Wed, 27 May 2009 21:14:39 +0200 (CEST)

Hi,

> you believe that there would be interest from the NETCONF/NETMOD community

Yes I believe this would be very interesting so I would encourage you
to try write your data model in YANG.  We would be very interested in
your feedback!

/martin

---

From: Simon Leinen <[email-masked]>
Date: Fri, 29 May 2009 17:34:18 +0200

> I would consider converting my draft to one that uses YANG, if you
> believe that there would be interest from the NETCONF/NETMOD community
> for me to do so.

I would also be interested in this, for two reasons: As an operator who
is likely to configure DHCPv6 servers in the future (we configure DHCPv4
servers, but currently use SAAC without DHCP for IPv6), and on the other
hand because I'd like to hear about your experiences as a "domain
expert" with YANG, e.g., learning curve & how happy you'll be with the
resulting YANG formulation of your configuration model.
-- 
Simon.