Information processing system

An information processing system comprising:

• at least two information processing devices being connected through a communication network so as to be communicated with each other in order to enable data transfer so that both of said information processing devices hold information data containing the same content, and each having a memory used to store said information data;
• and
• wherein said data stored in said memory is made up of unit data being split into a predetermined unit and said data is of a hierarchical tree structure in which nodes are expressed by tags and wherein each of said nodes existing in a lowest layer in said hierarchical tree structure corresponds to each piece of said unit data and to each of said tags expressing each of said nodes in said lowest layer are added identifying information used to identify each piece of said unit data and time information indicating a time of storing each piece of said unit data into said memory, and wherein each of said information processing devices includes a replication control unit which, by using said identifying information and said time information, detects inconsistent portion of said data held by each of said information processing devices and performs replication of said inconsistent portion of said data only between said information processing devices.