[NGO] Re: [YANG] YANG augment-stmt

Andy Bierman <ietf@andybierman.com> wrote:
> Hi,
> 
> Looking at the ABNF for the all-powerful augment statement,
> I notice it can appear inside a list or inside an another augment,
> anywhere a data-def-stmt can go in fact.
> 
> Since this clause does not instantiate any data where it
> located, but rather at the target specified by the augment-arg-str,
> the containment for the augment seems pretty much irrelevant,
> except that the augment could be nested within N different 'when'
> statements, nested inside obsolete nodes, etc.
> 
> The key in a list with an augment-stmt has no affect on the target data,
> does it?

I'm not sure I understand this question.

> What does it mean to have an augment inside a grouping, so that
> it is copied everywhere a 'uses' for that grouping is specified?
> 
> What is the use-case for augment inside augment?

The use case for augment inside anything but on the top-level is to be
used in combination with 'uses'.  The idea is that you can do 'uses
foo', and then in a following augment add new nodes to the foo
grouping:

  grouping server {
    leaf name { type string; }
    container address {
      leaf ip { type inet:ip-address; }
    }
  }

  container foo {
    uses server;
    augment address {
      leaf port { type inet:port-number; } 
    }
  }      

Or the same thing as a reusable grouping:

  grouping server-with-port {
    uses server;
    augment address {
      leaf port { type inet:port-number; } 
    }
  }      

This way extensions to groupings ("complex types":) can be defined.

> That means while you are defining extra data to attach to /acme:foo
> you also define some extra data for /a:bar/b:baz?

Yes.

> I have only seen augment examples that appear at the top-level.
> Are there real examples of data models that actually need to
> nest the augment-stmt anywhere and everywhere in the data model,
> even inside the 'input' clause for an RPC method definition?
> 
> What are the requirements for WG or vendor data model augmentation exactly?

I'm not sure I understand this question either.

/martin

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