You can execute the connection to the web service from another event instead of a button. For example, based on the value a user chooses from a list, you want to pass that value to the service.
In JavaScript: xfa.connectionSet.MyWSDLDataConnection.execute(0);
In FormCalc: $connectionSet.MyWSDLDataConnection.execute(0)
In both cases, the parameter being passed is a Boolean value. When the results are returned from the web service, this value indicates whether the entire data DOM should be merged with the form or whether the returned values will replace those in the current instance of the form. Zero (0) indicates that the data will not be remerged; that is, no new fields or subforms will be added or removed directly as a result of this execute operation. One (1) indicates that all data in the data DOM will be remerged.

To execute the connection to the web service