Re: [YANG] relation to XML PDUs

Martin Bjorklund wrote:
> Ladislav Lhotka <lhotka@cesnet.cz> wrote:
>> Hi,
>>
>> I understand that YANG data models describe entire configuration
>> datasets, but do they also pose any restrictions to the NETCONF XML
>> PDUs? For example: the order of children in a YANG model is fixed - does
>> it mean that the corresponding XML elements in PDUs must appear in the
>> same order?
> 
> Currently we do this, mainly b/c of the requirement to be XSD
> compatible, i.e. we want to be able to generate an XSD which can be
> used to validate the PDUs.
> 

Really?  Where is that documented?

Let's review the NETCONF PDUs so we can stop talking about
schema validation in high altitude abstractions.  I don't care about
abstract requirements, I care about running code.

There are 3 types of parameters for RPC operations:

  1) XML represents RPC parameter abstractions (e.g., error-option)
     XSD can validate these RPCs fine.

  2) XML represents subtree filter parameters
     XSD cannot do anything with this.  There are no requirements
     except well formed XML.  Unknown namespaces and elements
     are just 'no-match' conditions, not errors.

  3) XML represents config database fragment
     XSD cannot do much with this unless minOccurs=0 is set for
     every element and the NETCONF operation attribute is added
     everywhere it is allowed.  I have never seen an XSD that
     actually does this.  Instead they all model the config-database
     representation, not any particular PDU.

The <edit-config> and <copy-config> operations allow arbitrary subsets of
config data to be sent in a given PDU, with an almost infinite
number of permutations. A subset of those permutations will
actually be valid for a given data model.   Since YANG models
the data, not the XML, the number of 'extra' permutations in
a YANG schema can be reduced to almost zero.

Andy

> 
> /martin
> 
> 
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