A distributed computer system has computers storing data items each data item being assigned to one of a plurality of virtual directories. Each computer has at least one node of a virtual network(10) for directory look-up, with linking data comprising addresses of other nodes associated with the same virtual directory and software that, in response to an enquiry message either replies, identifying itself or forwards the message to another node of the network(10), according to whether the node is or is not associated with the directory specified in the enqiry message. Similarly, each computer has, for each item that it stores, a node of a virtual network for item look-up, with linking data comprising addresses of other such nodes associated with items assigned to the same virtual directory, so that these linking data together define a plurality of virtual networks for item look-up, each of which networks corresponds to a respective different virtual directory. The node also has software that, in response to an enquiry message either replies with the item sought(or identifying itself for later item retrieval) or forwards the message to another node of the network , according to whether the node is or is not associated with the item specified in the enqiry message. For use in this system, or separately, a retrieval mechanism for thereby the addresses (25) of multiuple nodes matching the same directory name(or other label) is described. Each node matching a given label(21a) has associated with it a data storage area for containing the label and is responsive to enquiry messages to return a list of addresses of other nodes matching the same label. First retrieval means responds to input of a label to identify the address of a node matching that label, and second retrieval means then sends an enquiry message to the address identified by the first retrieval means. |