Abstract: A system and methods are provided for operating and building graphically XML processing programs, guiding the user in development of the program, preventing and detecting development errors as the program is being designed, ensuring that the program is valid, i.e. satisfies required input and output constraints at all times, i.e. from the time it is developed to when it is deployed in a production environment, ensuring the automated change management if the internal logic of the Web service, or data sources called by the service or the schema that underlies the Web service are modified.