Online data retrieval system

Claim 1

A data retrieval system comprising a host computer in the memory of which data to be retrieved is stored, and a plurality of user terminals from which requests (for data are transmitted to the host and to which data retrieved in response to such requests is transmitted from the host, wherein data is stored in the host computer in the form of a series of search terms arranged in a predetermined logical order, each stored search term being stored with respective associated data to which users require access, and data retrieval requests are entered by users in the form of search terms corresponding in logical structure to the search terms stored in the host computer, characterised in that the host computer memory is partitioned into a series of blocks in each of which is stored search terms falling within a respective predetermined range of the logical order and the data associated with the search terms falling within the predetermined range, each user terminal comprises a memory in which is stored an index that cross references the memory address of each block in the host memory with the range of search terms stored within that block, each user terminal comprises means responsive to entry of a search term to identify from the index the memory address of the block storing the range of search terms including the entered search term, each user terminal comprises means for transmitting an identified memory address to the host, the host computer comprises means for transmitting the content of the block identified by a received memory address to the user terminal from which the received memory address was transmitted; wherein each said block of memory is allocated a range of searc terms selected such that a substantial portion of each said block will be unoccupied by data to provide for expansion of the volume of data to be stored; and wherein the portion of each said block which is occupied by useful data is flagged and the host computer transmitting means is arranged to transmit only that portion of a selected block which is occupied by said useful data, and each user terminal comprises means for displaying data transmitted to it from the host.