Disclosed are methods and apparatus for effectively mediating communications between entities in a computer network. In general, a format preference for a first service is received into a message interchange network. The format preference specifies an expected format for messages received by such first service without specifying a format for any other services. The format preference for the first service is then stored in a repository associated with the message interchange network. Messages sent to the first service are then mediated using the format preference stored for the first service so that the first service receives messages in the expected format specified by the format preference stored for the first service.