Patent ID: 6990561

Claim:
A data sharing method in which data is shared within a group composed of a plurality of terminals interconnected via a network, comprising: in the case an update is generated for shared data which is shared by the group; each of the plurality of terminals uniquely determining in a simultaneous multicast transmission terminal determination step which of any one of the plurality of terminals is to be a simultaneous multicast transmission terminal that simultaneously transmits update information relating to updating to each terminal within the group according to a predetermined determination method by each of the terminals, transmitting from each terminal in a transmission step update information to the simultaneous multicast transmission terminal determined in the simultaneous multicast transmission terminal determination step, said simultaneous multicast terminal simultaneously transmitting in a simultaneous multicast transmission step update information to the plurality of terminals corresponding to member data which is memorized in advance by the simultaneous multicast transmission terminal, and updating in an updating step shared data according to the received update information in each terminal that has received the simultaneously transmitted update information, wherein said simultaneous multicast transmission terminal is uniquely determined in accordance with the update information which is received by each of the terminals in said simultaneous multicast transmission step.