Re: Poll for consensus on edit operations

[Juergen Schoenwaelder <j.schoenwaelder@iu-bremen.de>]

On Wed, Mar 31, 2004 at 09:05:03AM -0800, Andy Bierman wrote:

> I'll work on that, but I probably won't get to it for a few days.
> 
> The decision tree isn't that complex:
> 
> 1) Should netconf protocol details (currently only applies to
>    the 'operation' attribute used for <edit-config>) be encoded
>    as attributes within user data models?
>    (I think WG consensus is leaning to no, but still undecided.)
> 
>    If yes) we're done
>    If no) continue
> 
> 2) Now a new mechanism to identify the start node of an edit-config
>    action is needed.  Here there are some issues which might impact
>    each other:
> 
>    - Should implementation of Xpath be mandatory for this purpose?
>      (I think the WG consensus is no.  We already decided not
>       to add the #xpath capability in v1.0)

I think not using xpath will be a pain in the longer term since we
will have to stick with a rather restricted model to select and
identify instances for ever.
 
>      - If so, it it okay to constrain the Xpath feature set to
>        simple expressions? (E.g., absolute path from the start of 
>        the <config> contents /foo/bars/bar)

I rather prefer to use xpath and to constrain xpath if people are
really worried about the xpath complexity. This at least allows a
clean forward migration path (and also implementations can distinguish
themself by supporting more or less xpath functionality).

>        - Do instance identifiers need to be part of the Xpath expression
>          for this purpose?  The agent instrumentation will know
>          if it's okay to create "bar.7", so isn't the path /foo/bars/bar
>          good enough?

I think requiring instances identification in the path is problematic;
I would prefer a URI based naming system and URIs in the middle of the
path look kind of strange. In other words, I prefer a scheme where an
object is named by a specific URI attribute. Of course, this implies
that you can not restrict xpath expression to just simple paths.
 
>    - Should edit-config be limited to one edit action per RPC?
>      (I think the WG consensus is no)
>      - If no, and no Xpath, then decide to find another way to 
>        specify the start-point.
> 
>   - Does the start-point even need to be specified by the application?
>     - The start point is always the data model root for merge and replace.
>     - Modify is not really a problem because the agent can tell 
>       that if elements like <foo> and <bars> are being used just
>       to specify the path to <bar>, or if actual parameters are
>       being modified.  The "must exist" test still applies to
>       the whole path.
>     - The start point is only important for create and delete actions
>       because a data model can have nested dynamic objects, which
>       creates ambiguity as to the intended node(s) for the edit action.

There are cases where you have to identify the object you want to
delete and it depends on the naming system how this is done. With
xpath, you can probably do this for whatever naming system we will
end up with. If netconf only supports simple path, then the choices
for the naming system are rather fixed.

Note, for create it might be important to specify that something is
created "before" or "behind" an existing object and so either the
manager is able to generate URIs or the manager has a way to express
such a constraint and the agents generates a suitable object and URI
^W name (what I would prefer).

/js

-- 
Juergen Schoenwaelder		    International University Bremen
<http://www.eecs.iu-bremen.de/>	    P.O. Box 750 561, 28725 Bremen, Germany

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