1. A machine implemented method for processing data, the method comprising: initiating, by a first data processing system, a negotiation of synchronization mode between the first data processing system and a second data processing system, for a first data class and a second data class; transmitting, by the first data processing system, first data representing changes to the first data class, from the first data processing system to the second data processing system, wherein the transmitting of the first data begins before completing the negotiation of the synchronization mode for the first data class; transmitting, by the first data processing system, second data representing changes to a second data class from the first data processing system to the second data processing system, wherein transmitting the second data begins before receiving the response to the transmitting of the first data; and receiving, at the first data processing system, a response to the transmitting of the first data, the response to the transmitting of the first data comprising completing the negotiation of the synchronization mode for the first data class; and receiving, at the first data processing system, a response to the transmitting of the second data, the response to the transmitting of the second data comprising completing the negotiation of the synchronization mode for the second data class, wherein the synchronization mode for the first data class is independent of the synchronization mode for the second data class.