Re: [Netconf] Representing URLs

[Andy Bierman <[e-mail]>]

On Tue, Dec 3, 2013 at 7:39 AM, Wojciech Dec <[e-mail]> wrote:

> Following up some of my earlier questions... Inline...
> ...
> >> 3. Use of current() function as predicate in URIs/URLs
> >>
> >> It would be useful to be able to use the "current()" function to
> construct
> >> URIs/URLs returned in Restconf. The spec does not make it clear on
> whether
> >> this would actually work in A or B above. Would it, or is there some
> other
> >> way?
> >>
> >
> >
> > The URI is not an XPath expression. There are no predicates allowed,
> > I don't think current() is allowed outside a predicate.
>
> Ok, so what is the way in Yang to have a predicate (e.g. current())
> based expression that ends up being represented as a URI in Restconf?
> Use of the current() predicate in the instance-identifier appears not
> to be supported (at least by pyang).
>
>
There is none. An instance identifier is the absolution path from root
to the specific node being identified.  It cannot be used for another
purpose.  The ietf-yang-types module has an xpath1.0 typedef
that allows current() in a predicate.

Here is the ABNF from RFC 6020:

 node-identifier     = [prefix ":"] identifier

 ;; Instance Identifiers

   instance-identifier = 1*("/" (node-identifier *predicate))

   predicate           = "[" *WSP (predicate-expr / pos) *WSP "]"

   predicate-expr      = (node-identifier / ".") *WSP "=" *WSP
                         ((DQUOTE string DQUOTE) /
                          (SQUOTE string SQUOTE))

   pos                 = non-negative-integer-value





> Thanks,
> Wojciech.
>
>
Andy