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. The system includes a graphical XML Programming system where XML processing programs are built and represented in a graphical fashion, a real-time metadata computation and visualization method for each selected execution point in the visual program that provides guided programming, error prevention and detection, and change impact analysis and change management, and, an automated execution path exploration method that enables overall program validation and error identification. The system and methods allow a user to reduce by at least a factor of 2 the costs of development and maintenance of reliable XML processing programs such as Web Services.