Re: NETCONF Instance Identifiers

[Martin Bjorklund <mbj@tail-f.com>]

Juergen Schoenwaelder <j.schoenwaelder@iu-bremen.de> wrote:
> On Mon, Oct 16, 2006 at 07:49:31PM +0200, Martin Bjorklund wrote:
>  
> > > Using xpath (or a subset of it) is fine with me. I note, however, that
> > > once we go down this path, we have a situation where we use instance
> > > identifiers where subtree filtering is unable to select such
> > > instances.
> > 
> > You mean b/c of the use of position()?  I assume that position() would
> > be used only when the data model indicates that there is a set of
> > instances, but they don't have a key.  So I guess the real issue is
> > that if the data model allows instances without keys, then subtree
> > filtering can't be used to select such instances.
> 
> This argument sounds backwards to me. We either allow things like
> position() or we don't.
> 
> If we allow such things (which I do like and support), then we simply
> have an instance identification mechanism which has more expressive
> power than subtree filtering has (and it is IMHO irrelevant whether
> you have other keys that can identify the same instance or not).

Ok.  So you mean that these two identifiers would be ok?

   /interface[name="eth0"]  and  /interface[2]

One problem with the second alternative is that it's difficult to know
whether the string will identify the same object over time, since
interfaces might come and go.

> I strongly dislike an approach where certain xpath features (like
> position()) may only be used under some conditions.

Are you suggesting that any XPath construct should be valid in an
Instance Identifier?  Or do you mean that if position() can be used in
some places in an Instance Identifier, then it should be possible to
use it anywhere in the Instance Identifier?


/martin

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