XPath usage overview
You can use XPath in your BPEL processes as part of assign activities or in conditions and expressions.
Assign activity
You can use XPath to reference parts of a BPEL variable as from-statement or as to-statement in an assign activity. The referenced part of the from-statement is copied and set to the indicated to-statement part. If the to-statement part is not initialized yet, it is automatically created for you. This also implies that all intermediate business object parts are created if necessary. To assign a string to the XPath /deliveraddress/street as shown in the screen capture below, the property deliveraddress of type Address does not need to exist. Even the BPEL variable customer does not need to be initialized before; instead, it is created automatically by the assign activity.
An XPath expression can reference simple data types, such as strings and integers, and complex data types. When you use the BPEL process editor, there is no verification that an assignment is correct regarding the data type of from-statement and to-statement parts. If you assign a part of a BPEL variable that is a simple data type, the IBM® Process Server converts it to the appropriate target simple data type if applicable. For example, you can assign an integer value to a string part of a variable. Nevertheless, if you are working with business objects, the data is not converted. You must make sure to assign only parts which are either convertible (simple types) or identically typed (simple types and business objects).
While you can use arbitrary XPath functions (see BPEL processes: Predefined XPath extension functions) for the from part of an assign activity, support for using them on the to part is limited to the child:: and attribute:: axes. For more information, see technote http://www-1.ibm.com/support/docview.wss?&uid=swg21222985.
Be sure to address the to part by an XPath statement without functions, (for example, /customers/address[1]/name). If you fill an array property using assign activities, be sure to access them sequentially for the to part. For example, you must fill /customers/address[1]/name before you fill /customers/address[2]/name (array indexes in XPath start with index 1). Otherwise, you get an exception during execution in IBM Process Server, which is thrown as the standard fault bpws:mismatchedAssignmentFailure. Also note that sibling functions are not allowed in a to-statement, if the referenced node has not been initialized before.
Conditions and expressions
At several places in the BPEL process editor, you can also use XPath-based conditions and expressions. This includes conditions on links in parallel activities, the join behavior on arbitrary activities within parallel activities, conditions in choice activities and while loop activities, expressions in the wait activity and the timeout expression in the receive choice activity. In addition, the ForEach activity can use XPath for its start and end expressions, as well as an XPath condition for its exit criterion.
In assign activities, XPath statements are used to reference a from-part and a to-part to be used for an assignment. Nevertheless, conditions and expressions must have a specific return value. Therefore, you must make sure your XPath points to a part in a BPEL variable that has the appropriate type (for example, Boolean for conditions). Otherwise, you must use XPath to build such a type, (for example, bpws:getVariableData("customer", "deliveraddress/zip")="12345").