1. A development environment for developing a data transfer interface, for converting message traffic between a sending data system having a first data structure and a receiving data system having a second data structure, the environment comprising: a first structure modeler for providing, from at least one sample message of each of a predetermined group of message types, a first data structure model for each of said message types; a second structure modeler for developing, from second system responses to test data, a second data structure model for each of said message types; and a matcher associated with said first structure modeler and said second structure modeler, for supporting matching of elements of said first structure model to corresponding elements of said second structure model thereby to form a message type mapping.