establishing, on a message receiving device, a plurality of receiver message models, each receiver message model specifying a message format for interpreting application messages, each receiver message model comprising one or more receiver field specifications, each receiver field specification specifying a message field for storing data in an application message, each receiver field specification comprising receiver field characteristics;

calculating, by the message receiving device, a receiver version number for each receiver message model in dependence upon the receiver field characteristics of one or more of the receiver field specifications of the receiver message model;

receiving, by the message receiving device from the message sending device, the application message and the sender version number for the sender message model; and

selecting, by the message receiving device, one of the plurality of receiving message models for interpreting the application message in dependence upon the sender version number for the sender message model and the receiver version numbers for the receiver message models.