Hi,

http://trac.tools.ietf.org/wg/netconf/trac/wiki/Issues_4741bis#issue-007

This issue was discussed at the NETCONF session today.

The question is what the resulting XML from an XPath filter looks
like.  For example, with this data model:

   list interface {
     key name;
     ...
     leaf mtu { ... }
   }

What should the expression: select="/interface/mtu" return?

1.  (no keys)

    <nc:data>
      <if:interface>
        <if:mtu>1500</if:mtu>
      </if:interface>
      <if:interface>
        <if:mtu>1500</if:mtu>
      </if:interface>
    </nc:data>


2.  (keys)

    <nc:data>
      <if:interface>
        <if:name>eth0<if:name>
        <if:mtu>1500</if:mtu>
      </if:interface>
      <if:interface>
        <if:name>eth2</if:name>
        <if:mtu>1500</if:mtu>
      </if:interface>
    </nc:data>


At least two implementations (mine and Andy's) return the keys, as in
alternative 2.


I suggest we add this to 8.9.1:

    The response message contains the subtrees selected by the filter
    expression.  For each such subtree, the path from the data model
    root node down to the subtree, including any elements or
    attributes necessary to uniquely identify the subtree, are
    included in the response message.


This is slightly different from how subtree filtering works.  Compare
these filters, with a data model where 'user' is a list with key
'name':

    <filter xmlns:t="http://example.com/schema/1.2/config"
            type="xpath"
            select="/t:top/t:users/t:user/t:company-info"/>

and

    <filter type="subtree">
      <top xmlns="http://example.com/schema/1.2/config">
        <users>
          <user>
            <company-info/>
          </user>
        </users>
      </top>
    </filter>

which look very similar.   The first one returns:

    <top xmlns="http://example.com/schema/1.2/config">
      <users>
        <user>
          <name>fred</name>
          <company-info>
            <id>2</id>
          </company-info>
        </user>
      </users>
    </top>

but the second one doesn't return any keys (which is not very
useful...)

    <top xmlns="http://example.com/schema/1.2/config">
      <users>
        <user>
          <company-info>
            <id>2</id>
          </company-info>
        </user>
      </users>
    </top>


Andy commented that his code returns the keys also in the subtree
filter case.  I'm not convinced the current text on subtree filtering
allows this, but maybe we should clarify that key nodes MAY be added
to the response message in subtree filtering.

Since the text on subtree filtering says: 

   The server does not need to utilize any data-model-specific
   semantics during processing,

we cannot say that the keys MUST be added, so a client that needs the
keys will still have to ask for them.


/martin