Hi,
A draft I have been working on
(https://datatracker.ietf.org/doc/draft-ietf-dhc-dhcpv6-yang/) contains a
number of XML configuration examples. During the XML expert review, a question
has been raised about the use of XML namespaces in these examples. I’m raising
it here as I don’t have the XML knowledge to answer.
In my example:
<interfaces xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
<interface>
<name>eth0</name>
<type>ianaift:ethernetCsmacd</type>
<description>DHCPv6 Relay Interface</description>
<enabled>true</enabled>
</interface>
</interfaces>
The question is related to the use of the ‘ianaift:’ prefix. This is quite
commonly use in XML examples in YANG documents (e.g. RFC8344) so I think the
question is generally applicable.
The specific comments from the expert review are:
-
For the correct processing of these documents requires that whatever XML
software is being used makes available to application code the namespace
prefixes.
Whilst the recommended tools (e.g. yanglint) provides this function, it is not
an XML best practice. Quoting from the Namespaces in XML, section 4: "Note that
the prefix functions only as a placeholder for a namespace name. Applications
SHOULD use the namespace name, not the prefix, in constructing names whose
scope extends beyond the containing document.”
I think that violating a SHOULD assertion in a W3C standard is a problem.
There is no requirement for XML processors to provide this prefix information,
and software that (quite legally) doesn't, will not work correctly with YANG
documents constructed as specified in this I-D.
1, YANG specifications should note this fact and specify that software which is
used to process YANG documents MUST provide an interface such that applications
can retrieve the prefix-namespace mappings.
2, For constructs such as <type>ianaift:ethernetCsmacd</type> the
Internet-Draft should specify that the prefix ("ianaift" in this case) MUST be
identical to the xmlns namespace prefix representing the namespace name
urn:ietf:params:xml:ns:yang:iana-if-type
3, Alternately, the draft could specify that for the namespace
urn:ietf:params:xml:ns:yang:iana-if-type, the XML namespace prefix ianaift MUST
be used. Another XML bad practice because software that generates XML
programmatically should feel free to generate synthetic prefixes without
breaking the content, but at least this would solve the problem.
-
BCP216 (RFC8407 - Guidelines for Authors and Reviewers of Documents Containing
YANG modules) doesn’t make any mention of how XML namespaces should be used,
only that example XML/ JSON should be included and that these examples need to
be validated (pyang and yanglint are mentioned for this).
Does this guidance need to be updated to reflect expert review comments above?
Thanks,
Ian
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