Abstract: In a cooperative computer based system for editing a web document including a plurality of clients a server, the cooperative computer based system includes means for generating editing instructions, converting editing instructions to a message related to editing and transmitting the message related to editing to the server; means for determining if the web document can be modified, based on the message related to editing; modifying contents of a copied web document stored in the server in conform to the message related to editing; and transmitting the message related to editing to the plurality of the clients; and means for modifying contents of the copied web document stored in each of the plurality of the clients in conform to the message related to editing transmitted from the server.