The most common method is through the use of the GenerateExtractWebService business rule, which may be attached to a transaction. Here is the format:
Math variables may be used in the message XML similar to how they are substituted in math variables of TYPE="SQL".
In some later versions there is also a math variable of TYPE="WebService" which is available, though it is more complex.
Note that in Version 9 this very inflexible method has been replaced with the pre-built web service connector extension, or the option to write custom extensions if desired, which provides support for standards like WS-Security and so forth as well as much more dynamic message formatting.
Edited by: user9954795 on Jul 28, 2010 2:07 PM