Re: [yang-doctors] Yangdoctors last call review of draft-ietf-ospf-yang-09

[Juergen Schoenwaelder <[e-mail]>]

On Mon, Jan 15, 2018 at 11:10:13AM +0100, Ladislav Lhotka wrote:
> On Mon, 2018-01-15 at 10:53 +0100, Juergen Schoenwaelder wrote:
> > On Mon, Jan 15, 2018 at 10:38:19AM +0100, Ladislav Lhotka wrote:
> > > > 
> > > > The intention (for better or worse) was that the value would use the
> > > > prefix used in imports.  This means that if you want to do any kind of
> > > > comparision of the string value to some known identities, then you
> > > > must import that module so that there is a prefix defined.  This was
> > > 
> > > This is IMO not true. As I already wrote, for using a when expression like
> > > 
> > >    when "../type = 'ospf:ospfv3'"
> > > 
> > > it is not necessary to import the "ietf-ospf" module and thus have the
> > > "ospf"
> > > prefix defined. If you think it is necessary, then point me to the relevant
> > > text.
> > 
> > Prefixes assigned to modules using the prefix statement are not
> > guaranteed to be globally unique. It is possible to have multiple
> > modules defining the prefix 'ospf', e.g.:
> > 
> >  module ietf-ospf {
> >    prefix ospf;
> >  }
> > 
> >  module acme-ospf {
> >    prefix ospf;
> >  }
> > 
> > Note that this is not a problem since YANG allows to redefine the
> > prefix in an import statement in case a prefix clash occurs. Hence,
> > the 'ospf' prefix in the when statement has to refer to the prefix
> > that is used in the module where the when statement is defined. And
> 
> In my example, the prefix is used inside an XPath string, and XPath 1.0 doesn't
> allow for adding any structure or semantics to the string type. So even if RFC
> 7950 stated that such an import was necessary (which it doesn't), it would be an
> improper use of XPath.
> 
> YANG can define the string value of a node instance in the conceptual data tree
> but a literal XPath string is just that.
> 
> Lada
> 
> 
> > because of that it is necessary to import a module that defines the
> > prefix 'ospf'. Any other interpretation would be ambiguous I think.

Fine, so this construction should be avoided since it is ambiguous.

/js

-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
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