Re: merge/replace selection criteria

[Paul Sangree <psangree@cisco.com>]

> Another valid-but-wrong interpretation would be replacing all
> users.
Actually since the operator="replace" is on the <user> element, I think at 
most one <user> would be replaced.

> The interpretation depends on the understanding of
> identifiers (identifying elements), but how should this be
> expressed inside the protocol? Or does it need to be, given
> that code handling users will either know what the identifiers
> are or learn them from the schema file?
IMHO, the selection keys (i.e. identifiers) should be explicit rather than 
making any assumptions that the target system knows which elements are 
keys.  There are several advantages to going this route:
(1) The code that processes an edit-config operation can be generic for a 
given configuration document format.  For example, the same code could edit 
any XML document.
(2) The management tool that generates the edit-config request does not 
have to know which fields are valid keys, since any element or attribute 
can be used as a key,
(3) Depending on the desired result, different fields can be used as 
keys.  Referring to the user list example, either <address> or <name> could 
be used as the key depending on the requestor's intent.

One partial solution that comes to mind is to put a key="key" attribute on 
each element to be used as a selection key.  In the example below, the 
<name> element is marked as a key to indicate that only the <user> whose 
<name> is "Bill Baker" is to be replaced.

<rpc message-id="12345" xmlns="http://ietf.org/xmlconf/1.0/base";>
<edit-config>
   <target>
      <running/>
   </target>
   <config xmlns="http://example.com/schema/userconf"; 
xmlns:xc="http://ietf.org/xmlconf/1.0/base";>
      <users>
         <user xc:operation="replace">
            <name key="key">Bill Baker</name>
            <address>123 A Street</address>
         </user>
      </users>
   </config>
</edit-config>

I say this is only a partial solution because it has some problems:
(1) Only elements (not attributes) can be marked as keys,
(2) It does not provide semantics to express "replace the <user> whose 
<name> is 'Bill Baker' with a <user> whose name is 'William Baker'".


Paul Sangree


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