Details
-
New Feature
-
Status: Closed
-
Major
-
Resolution: Fixed
-
1.2
-
None
-
Platform-Independent
Description
This is a description of a facility to make changes to instances of the XPath 2.0 data model. This will come in handy in these types of scenarios: modifying XML messages, adding to existing XML documents, creating edited copies, etc. In particular, it will allow you to perform any or all of the following operations on an XDM instance:
- Insertion of a node
- Deletion of a node
- Renaming a node
The building blocks of our update facility are XPath functions, all of which take a context node, a copy of which is modified in some way and in turn returned. Below, we describe the update syntax in terms of XPath extension functions, and its semantics in terms of XQuery Update expressions. We wrote our (non-updating) functions along the lines of corresponding (updating) XQuery Update expressions, in such a way that the two are interchangeable (i.e., once we add support for the xquery expression language.) Note that, by default, XQuery Update modifies nodes in-place, whereas our XPath functions modify a copy.
Use Case: Insert Siblings Before Children Of Context Node
Description: A function to insert the node(s) specified by $siblings before the first node specified by $children, all of whose nodes must have $context as parent.
Signature:
ode:insert-before($context as node(), $children as node(), $siblings as node()) as node()
Example:
<assign>
<copy>
<from>ode:insert-before($parent, $parent/child::node[position()=last()], $siblings)</from>
<to variable="parent"/>
</copy>
</assign>
Semantic: The above snippet is equivalent to the XQuery expression:
insert nodes $siblings before $parent/child::node[position()=last()]
Use Case: Insert Siblings After Children Of Context Node
Description: A function to insert the node(s) specified by $siblings after the last node specified by $children, all of whose nodes must have $context as parent.
Signature:
ode:insert-after($context as node(), $children as node(), $siblings as node()) as node()
Example:
<assign>
<copy>
<from>ode:insert-after($parent, $parent/child::node(), $siblings)</from>
<to variable="parent"/>
</copy>
</assign>
Semantic: The above snippet is equivalent to the XQuery expression:
insert nodes $siblings after $parent/child::node()
Use Case: Insert As First Children Of Context Node
Description: A function to insert the node(s) specified by $children as the first child(ren) of $context.
Signature:
ode:insert-as-first-into($context as node(), $children as node()*) as node()
Example:
<assign>
<copy>
<from>ode:insert-as-first-into($parent, $children)</from>
<to variable="parent"/>
</copy>
</assign>
Semantic: The above snippet is equivalent to the XQuery expression:
insert nodes $children as first into $parent
Use Case: Insert As Last Children Of Context Node
Description: A function to insert the node(s) specified by $children as the last child(ren) of $context.
Signature:
ode:insert-as-last-into($context as node(), $children as node()*) as node()
Example:
<assign>
<copy>
<from>ode:insert-as-last-into($parent, $children)</from>
<to variable="parent"/>
</copy>
</assign>
Semantic: The above snippet is equivalent to the XQuery expression:
insert nodes $children as last into $parent
Use Case: Delete Children From Context Node
Description: A function to delete the node(s) specified by $children from its parent specified by $context.
Signature:
ode:delete($context as node(), $children as node()*) as node()
Example:
<assign>
<copy>
<from>ode:delete($parent, $children)</from>
<to variable="parent"/>
</copy>
</assign>
Semantic: The above snippet is equivalent to the XQuery expression:
delete nodes $children
Use Case: Rename Context Node:
Description: A function to rename the context node specified by $context as per the name specified by $item, which is either a QName, Element or String.
Signature:
ode:rename($context as node(), $name as item()) as node()
Example:
<assign>
<copy>
<from>ode:rename($person, fn:QName("http://www.example.com/example", "manager"))</from>
<to variable="person"/>
</copy>
</assign>
Semantic: The above snippet is equivalent to the XQuery expression:
rename $person as fn:QName("http://www.example.com/example", "manager")
Unlike XQuery Update, we designed our functions to be non-updating in that they preserve the identity and properties of its arguments (i.e., they don't try to change the XML in-place). Instead, a modified copy of the context node is created, essentially giving it a new identity. Further, all of our functions return a single R-value item, as opposed to a sequence. This allows us to not only honor WS-BPEL's static analysis requirements, but also be friendly to the copy operation of WS-BPEL's assign activity. In particular, it ensures that:
(a) Our functions are safe to use in the from-spec of the copy operation (no in-place updates must occur here.)
(b) The burden of modifying XML messages remains with the copy operation (all updates are reflected only here.)
(c) The node replacement semantics of the copy operation is not impacted (the entire target node is replaced.)
(d) The modified copy of the context node can be moved to a new location (target need not be the context node.)
