Path Descriptors

Microsoft XML Diff

Microsoft XML Diff 1.0 and XML Patch 1.0

Path Descriptors

The XML Diff Language (XDL) uses path descriptors to identify the nodes in the source XML document. Path descriptors work on DOM data model, and use the node position as the core identifier for the nodes. XDL does not use XPath because the XPath data model differs from DOM.

All path descriptors refer to the original source XML tree before any changes are applied. So when the path descriptor applies to the first node of the source tree, which has been changed to be the third node in the changed tree, the path descriptor for this node is "1" as the node is first in the source document (the source document is a base).

The XDL Diffgram shows what nodes have been modified, added, or removed. It uses the words change, add, or remove inside the XDL to describe the change. Next, it describes what node the changes took place on, by giving a path descriptor, and then indicates what the changes were.

Here is the formal grammar used by the path descriptors.

Attribute         :==   '@'Name

NodePosition   ::=      Digit+

AttributeList      :==   Attribute ( '|' Attribute )*

PathDescriptor   ::= NodeList | AttributeList

   NodeList          ::= RelativeNodeList | AbsoluteNodeList

        RelativeNodeList ::= NodeInterval ( '|' NodeInterval )*

        AbsoluteNodeList ::= '/' (NodePosition'/')* RelativeNodeList

        NodeInterval      ::=  NodePosition  |  NodePosition '-' NodePosition

The following table shows some examples of path descriptors, and provides an explanation of the path descriptors.

Example path descriptor Explanation
3 Means the third child node of the current node.
1-2 Means the first and second child of the current node.
1-2|5 Means the first, second, and fifth child of the current node.
/1/2 Means the second child of the first node at the root level.
1/2/3-6 Means the third, fourth, fifth, and sixth child of the second child of the first node at root level.
@value Means the attribute named value.
@value | @type Means the attribute named value and the attribute named type.

The path descriptors are used in the XDL Diffgram to identify nodes in the original document. The XDL Diffgram contains elements qualified with the xd: prefix associated with the namespace The XDL Diffgram element names indicate what action has occurred (for example add, remove, change). The attributes of the XDL Diffgram element and the element content then specifies the details of the operation, for example which nodes are affected, new values of the nodes, and so on.

See Also

XML Diff Functionality | XML Diff Language (Diffgram) | XmlDiff Operation xd:node | XmlDiff Operation xd:add | XmlDiff Operation xd:remove | XmlDiffOperation xd:change | Extended Operations | Example of a Diffgram |XmlDiff Class

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