The starting point for data manipulation in BPEL is the assign activity, which builds on the XPath standard. XPath queries, expressions, and functions play a large part in this type of manipulation.

In addition, more advanced methods are available that involve using XQuery, XSLT, or Java, usually to do more complex data transformation or manipulation.

This section provides a general overview of how to manipulate XML data in BPEL. It summarizes the key building blocks used in various combinations and provides examples. The remaining sections in this chapter discuss and illustrate how to apply these building blocks to perform specific tasks.

You use the assign activity to copy data from one XML variable to another, or to calculate the value of an expression and store it in a variable. A copy element within the activity specifies the source and target of the assignment (what to copy from and to), which must be of compatible types.

The following example shows the formal syntax for BPEL version 1.1, as described in the Business Process Execution Language for Web Services Specification:

<assign standard-attributes>
   standard-elements
   <copy>
      from-spec
      to-spec
   </copy>
</assign>

The next example shows the formal syntax for BPEL version 2.0, as described in the Web Services Business Process Execution Language Specification Version 2.0. The keepSrcElementName attribute specifies whether the element name of the destination (as selected by the to-spec) is replaced by the element name of the source (as selected by the from-spec) during the copy operation. When keepSrcElementName is set to no (the default value), the name (that is, the namespace name and local name properties) of the original destination element is used as the name of the resulting element. When keepSrcElementName is set to yes, the source element name is used as the name of the resulting destination element.

<assign validate="yes|no"? standard-attributes>
   standard-elements
   (
   <copy keepSrcElementName="yes|no"? ignoreMissingFromData="yes|no"?>
      from-spec 
      to-spec
   </copy>
   . . .
   . . .
</assign>

This syntax is described in detail in both specifications. The from-spec and to-spec typically specify a variable or variable part, as shown in the following example:

<assign>
   <copy>
      <from variable="c1" part="address"/>
      <to variable="c3"/>
   </copy>
</assign>

When you use Oracle JDeveloper, you supply assign activity details in a Copy Rules dialog that includes a From section and a To section. This reflects the preceding BPEL source code syntax.

XPath standards play a key role in the assign activity. Brief examples are shown here as an introduction. Examples with more context and explanation are provided in the sections that follow.

• XPath queries

  An XPath query selects a field within a source or target variable part. The from or to clause can include a query attribute whose value is an XPath query string. The following code provides an example:

  <from variable="input" part="payload"
        query="/p:CreditFlowRequest/p:ssn"/>
  

  The value of the query attribute must be a location path that selects exactly one node. You can find further details about the query attribute and XPath standards syntax in the Business Process Execution Language for Web Services Specification (section 14.3) or Web Services Business Process Execution Language Specification Version 2.0 (section 8.4), and the XML Path Language (XPath) Specification, respectively.

• XPath expressions

  You use an XPath expression (specified in an expression attribute in the from clause) to indicate a value to be stored in a variable. For example:

  <from expression="100"/>
  

  The expression can be any general expression (that is, an XPath expression that evaluates to any XPath value type). Similarly, the value of an expression attribute must return exactly one node or one object only when it is used in the from clause within a copy operation. For more information about XPath expressions, see section 9.1.4 of the XML Path Language (XPath) Specification.

Within XPath expressions, you can call the following types of functions:

• Core XPath functions

  XPath supports a large number of built-in functions, including functions for string manipulation (such as concat), numeric functions (such as sum), and others.

  <from expression="concat('string one', 'string two')"/>
  

  For a complete list of the functions built into XPath standards, see section 4 of the XML Path Language (XPath) Specification.

• BPEL XPath extension functions

  BPEL adds several extension functions to the core XPath core functions, enabling XPath expressions to access information from a process.

  • For BPEL 1.1, the extensions are defined in the standard BPEL namespace http://schemas.xmlsoap.org/ws/2003/03/business-process/ and indicated by the prefix bpws:

    <from expression= "bpws:getVariableData('input', 'payload', '/p:value') + 1"/>
    

    For more information, see sections 9.1 and 14.1 of the Business Process Execution Language for Web Services Specification. For more information about getVariableData, see getVariableData.

  • For BPEL 2.0, the extensions are also defined in the standard BPEL namespace http://schemas.xmlsoap.org/ws/2003/03/business-process/. However, the prefix is bpel:

    <from>bpel:getVariableProperty('input', 'propertyName')</from>
    

    For more information, see section 8.3 of the Web Services Business Process Execution Language Specification Version 2.0. For more information about getVariableProperty, see getVariableProperty (For BPEL 2.0).

• Oracle BPEL XPath extension functions

  Oracle provides some additional XPath functions that use the capabilities built into BPEL and XPath standards for adding new functions.

  These functions are defined in the namespace http://schemas.oracle.com/xpath/extension and indicated by the prefix ora:.

• Custom functions

  Oracle BPEL Process Manager functions are defined in the bpel-xpath-functions-config.xml file and placed inside the orabpel.jar file. For more information, see Creating User-Defined XPath Extension Functions.

Sophisticated data manipulation can be difficult to perform with the BPEL assign activity and the core XPath functions. However, you can perform complex data manipulation and transformation by using XSLT, Java, or a bpelx operation under an assign activity (See Manipulating XML Data with bpelx Extensions) or as a web service. For XSLT, Oracle BPEL Process Manager and Oracle Mediator includes XPath functions that execute these transformations.

For more information about XPath and XQuery transformation code examples, see Creating Transformations with the XSLT Map Editor and Creating Transformations with the XQuery Mapper.

For more information about the assign activity, see Assign Activity.