Subtree Filtering

Overview

Subtree filtering allows an application to include particular XML subtrees in the <rpc-reply> elements for a <get> or <get-config> operation.

Subtree filtering provides a small set of filters for inclusion, simple content exact-match, and selection. The NETCONF agent does not need to use any data-model-specific semantics during processing, allowing for simple and centralized implementation policies.

Subtree Filter Components

Each node specified in subtree filtering represents a filter. The filter only selects nodes associated with the basic data model of a specified database on the NETCONF server. A node matching any filtering rule and element hierarchy is selected. Table 1 describes subtree filter components.

• Namespace selection

  If the XML namespace associated with a specific node in the <filter> element is the same as that in the underlying data model, the namespace is matched.

  <filter type="subtree">
   <top xmlns="http://example.com/schema/1.2/config"/>
  </filter>

  In this example, the <top> element is a selection node. If the node namespace complies with http://example.com/schema/1.2/config, the node and its child nodes will be included in the filter for output.

• Containment node

  The child element of a containment node can be a node of any type, including another containment node. For each containment node specified in the subtree filter, all data model instances that completely match the specified namespace and element hierarchy, and any attribute matching expression are included in the output result.

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

  In this example, the <top> element is a containment node.

• Content match node

  A leaf node that contains simple content is called a content match node. It is used to select some or all of its sibling nodes for filter output and represents exact match of the leaf node element content.

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

  In this example, both the <users> and <user> nodes are containment nodes, and the <name> node is a content match node. Because the sibling nodes of the <name> node are not specified, only <user> nodes that comply with namespace http://example.com/schema/1.2/config, with their element hierarchies matching the name element and their values being fred, can be included in the filter output. All sibling nodes of the <name> node are included in the filter output.

  

  The support-filter statement in the YANG model indicates whether to support content filtering for a node when the node is being operated:

  1. Content filtering is supported for key nodes by default.

  2. Content filtering is not supported for non-key nodes by default. If the value of the support-filter statement is set to true for a non-key node, content filtering is supported.

• Selection node

  Selection nodes represent a basic data model for an explicit selection of filters. If any selection node appears in a group of same-level sibling nodes, the filter selects a specified subtree and suppresses the automatic selection of the entire sibling node set in the basic data model. In a filtering expression, an empty tag (such as <foo/>) or an expression with explicit start and end tags (such as <foo> </ foo>) can be used to specify an empty leaf node. In this case, all blank characters will be ignored.

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

  In this example, the <top> node is a containment node, and the <users> node is a selection node. The <users> node can be included for filter output only when the <users> node complies with namespace http://example.com/schema/1.2/config and is contained in the <top> element in the root directory of the configuration database.

Subtree Filter Processing