XQuery Update Facility: Insert Delete Replace Rename

The XQuery Update Facility extends XQuery to enable persistent modifications to XML documents without requiring full-document rewrites. Instead of altering nodes instantly, update expressions generate updating primitives that are collected into a Pending Update List (PUL) and applied together in a specific, safe execution order at the end of the query snapshot. The core of this mechanism relies on four primary expressions: insert, delete, replace, and rename.

The insert Expression

The insert expression adds new nodes into an existing XML tree. It supports directional and positional modifiers to define exactly where the source nodes should be placed relative to the target node.

• Syntax forms:
  • insert node $source into $target: Inserts the node as a child of the target element or document node, without a guaranteed position relative to existing children unless specified.
  • insert node $source as first into $target: Inserts the node as the first child of the target element.
  • insert node $source as last into $target: Inserts the node as the final child of the target element.
  • insert node $source before $target: Inserts the node as a sibling immediately preceding the target node.
  • insert node $source after $target: Inserts the node as a sibling immediately following the target node.

If attributes are inserted into an element, the positional keywords (before, after, first, last) are ignored because attributes are unordered.

The delete Expression

The delete expression removes one or more nodes from an XML document.

• Syntax:
  • delete node $target
  • delete nodes $targets

The target expression evaluates to a sequence of zero or more nodes. When executed, the targeted nodes (which can be elements, attributes, text nodes, comments, or processing instructions) are detached from their respective parent nodes. If a deleted element contains child nodes, the entire subtree is removed automatically.

The replace Expression

The replace expression updates XML content through two distinct operational modes: replacing an entire node or replacing only a node’s value.

• Replacing a Node (replace node):
  • replace node $target with $replacement
  • This form removes the target node and inserts one or more replacement nodes in its exact position. If the target is an attribute, the replacement must also be an attribute; if the target is an element, comment, text node, or processing instruction, the replacement must not be an attribute.
• Replacing Node Value (replace value of node):
  • replace value of node $target with $new-value
  • This form preserves the identity and attributes of the target node while altering its internal content. For element nodes, all existing children are removed and replaced with a single text node containing the string value of $new-value. For attribute, text, comment, or processing instruction nodes, the string value of the node is updated directly.

The rename Expression

The rename expression modifies the QName (qualified name) of an element, attribute, or processing instruction without altering its node identity, attributes, or child content.

• Syntax:
  • rename node $target as $new-name

The target expression must resolve to a single element, attribute, or processing instruction node. The $new-name expression evaluates to an xs:QName (or an xs:string representing the name). The operation preserves the node’s position, descendants, and attributes while updating only its name and associated namespace bindings.