Re: [NGO] Re: Why NETCONF needs a data modeling language

Juergen Schoenwaelder píše v Čt 29. 11. 2007 v 12:34 +0100:

> Statements like 'config true;' are essential for the processing of
> NETCONF messages and also for validating content exchanged in NETCONF
> messages (and this is why for example generic XML validation tools are
> only of limited value for NETCONF implementors).

Yes, I think pure RNG is not an option. But again, RNG is considerably
more open to extensions than XSD (no appinfo wrappers needed). However,
to be fair, using foreign elements/namespaces (and annotations)
seriously damages the readability of the compact syntax (not so much the
XML syntax). 

> a) that doing so will lead to a large reuse of available RNG tools for
>    processing NETCONF data models (since they don't know the RNG
>    subset nor the semantic additions)

For example, NETCONF data could be validated (as an XML document) using
the existing tools, RNG specification requires that foreign elements be
ignored. As for the subset of RNG - could it perhaps be just a
convention, like "avoid mixed content"?

> 
> b) that the effort to specify such an extended subset will be less
>    than the effort for defining a domain specific language like YANG

I'd say the former effort will be *significantly* smaller than the
latter since the main issue - defining document structure - comes for
free and has already been thoroughly tested. A problem may be though
that the hybrid language could turn out to be less readable for humans.

> 
> c) that the effort to implement tools understanding the adapted subset
>    of RNG will be less than writing proper tools for a domain specific
>    language from scratch

It would make sense if one could use both the traditional XML tools and
new NETCONF-specific tools. The big advantage would be that both
categories would use exactly the same data model specification. Even if
someone writes conversion tools like YANG->RNG, it would be more
difficult to guarantee consistency.

> 
> d) that there will be long term (say 20 year) reliable change control
>    exercised by the organization that has change control over NETCONF

For the extension within an IETF-controlled namespace this could be
guaranteed, but of course if the XML world turns entirely to Yet Another
Schema Language, the extension would have to be ported to it. Given the
momentum behind RNG these days, I don't think it is very likely.

Lada

-- 
Ladislav Lhotka, CESNET
PGP Key ID: E74E8C0C

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