Re: [netmod] leafref and identityref

Martin Bjorklund <mbj@tail-f.com> Mon, 21 October 2019 12:02 UTC

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Date: Mon, 21 Oct 2019 14:01:50 +0200 (CEST)
Message-Id: <20191021.140150.1807416568931644257.mbj@tail-f.com>
To: lhotka@nic.cz
Cc: netmod@ietf.org
From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] leafref and identityref
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Ladislav Lhotka <lhotka@nic.cz>; wrote:
> On Mon, 2019-10-21 at 13:40 +0200, Martin Bjorklund wrote:
> > Hi,
> > 
> > Ladislav Lhotka <lhotka@nic.cz>; wrote:
> > > Hi,
> > > 
> > > consider the following situation:
> > > 
> > > module A {
> > >   ...
> > >   prefix a
> > >   identity X;
> > >   leaf foo {
> > >     type identityref {
> > >       base X;
> > >     }
> > >   }
> > > }
> > > 
> > > module B {
> > >   ...
> > >   import A {
> > >     prefix a;
> > >   }
> > >   leaf fooref {
> > >     type leafref {
> > >       path "/a:foo";
> > >     }
> > >   }
> > > }
> > > 
> > > What is now a correct lexical form of fooref's value? Could it be just
> > > 'X', or is the prefix required, i.e. 'a:X'?
> > > 
> > > This is not very clear from RFC 7950 (sections 9.9.4 and 9.10.3). I am
> > > inclined to require the prefix.
> > 
> > 9.10.3 says:
> > 
> >    If the prefix is not
> >    present, the namespace of the identityref is the default namespace
> >    in effect on the element that contains the identityref value.
> > 
> > 
> > so the interpretation of a missing prefix in "fooref" is that the
> > identity is defined in module B.
> > 
> > (a missing prefix in "foo" means that the identity is defined in
> > module A)
> 
> To be more specific, here is an example instance:
> 
> <foo xmlns="...namespace of A...">X</foo>
> <fooref xmlns="...namespace of B...">X</fooref>
> 
> It can be argued that this is correct because (sec. 9.9.4):
> 
>    A leafref value is lexically represented the same way as the leaf it
>    references represents its value.
> 
> That is, the same lexical representation is assumed, which is exactly what we
> have in the example.

It doesn't say that the lexical value is exactly the same, but
"represented the same way" - so when the lexical representation is
context dependent we have this situation.

> It seems that we agree that it is incorrect, but then sec. 9.9.4 should be
> clarified.




/martin