Re: [netmod] Use XML namespaces in YANG document examples

Hi,

I think the text from sec 4 refers to the usage within an application.
The XML instance document is the on-the-wire representation and
the I-D example looks correct.

https://www.w3.org/TR/xml-names/#ns-qualnames

Andy

On Thu, Feb 3, 2022 at 3:53 AM tom petch <ietfc@btconnect.com> wrote:

> From: netmod <netmod-bounces@ietf.org> on behalf of ianfarrer@gmx.com <
> ianfarrer@gmx.com>
> Sent: 03 February 2022 09:37
>
> 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.
>
> <tp>
>
> Ian
>
> This looks like the issue I raised on this list 14jan2022 with a subject
> line of
> XML and prefix
> although I have not checked that the usage is exactly the same; the 'XML
> Expert' comment would appear to be.
>
> Tom Petch
>
> 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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