The present invention relates to logic systems which use a message-based API, and in particular to telecommunication systems. The present invention aims to overcome drawbacks in the way in which data is sent between, for example, a gatekeeper unit and a service application running on a service platform. By providing a formatter or formatter units on the gatekeeper units, incoming messages may be pre-processed thereby reducing the bandwidth requirements for data transfer. Each formatter unit may be specific to a service application, and ensures that data arrives at the service platform in the appropriate format.