In the following example, the BPEL XPath function getVariableData retrieves the value being incremented. The arguments to getVariableData are equivalent to the variable, part, and query attributes of the from clause (including the last two arguments, which are optional).

<assign>
   <copy>
      <from expression="bpws:getVariableData('input', 'payload',
          '/p:value') + 1"/>
      <to variable="output" part="payload" query="/p:result"/>
   </copy>
</assign>

You can also use $variable syntax in BPEL 1.1, as shown in the following example:

<assign>
  <copy>
    <from expression="$input.payload + 1"/>
    <to variable="output" part="payload" query="/p:result"/>
  </copy>
</assign>

The following example shows how to use $variable syntax in BPEL 2.0.

<assign>
   <copy>
      <from>$input.payload + 1</from>
      <to>$output.payload</to>
   </copy>
</assign>