Modern information systems may exploit numerous web services for communication. Each web service may exploit its own XML format for data representation which causes problems with their integration and evolution. Manual integration and management of evolution of the XML formats may be very hard. In this paper, we present a novel method which exploits a conceptual diagram. We introduce an algorithm which helps a domain expert to map the XML formats to the conceptual diagram. It measures similarities between the XML formats and the diagram and adjusts them on the base of the input from the expert. The result is a precise mapping. The diagram then integrates the XML formats and facilitates their evolution -a change can be made only once in the diagram and propagated to the XML formats.