1. An information processing apparatus comprising: a controller device comprising a data processing device; an input unit configured to input a plurality of new search keys, each new search key to be registered with a file for subsequent retrieval of the file based on a comparison involving the respective new search key, when registered, and a subsequently input search key that is input after registration of the respective new search key; a user information obtaining unit configured to, for each of the plurality of new search keys, obtain user information for identifying a user to be associated with the respective new search key; a group information obtaining unit configured to, for each of the plurality of new search keys, obtain group information for identifying a user group to be associated with the respective new search key; an addition unit configured to, for each of the plurality of new search keys, (a) form a composite search keyword from the respective new search key and the user information obtained by the user information obtaining unit or the group information obtained by the group information obtaining unit, and (b) add the composite search keyword to index information associated with the file for the subsequent retrieval of the file; a selection unit configured to select, for each of the plurality of new search keys and for the forming and adding performed by the addition unit, either the user information or the group information; and a registration unit configured to cause the index information, having the composite search keywords formed by the addition unit and added thereto by the addition unit according to the selection by the selection unit, to be registered with the file in a storage unit for the subsequent retrieval of the file, wherein each of the units is implemented at least in part by the controller device.
3. An information processing apparatus as claimed in claim 1 , further comprising a search unit configured to search files stored in the storage unit, based at least on a comparison of (a) each of at least some of the composite search keywords registered by the registration unit with (b) the subsequently input search key that is input after the registration of at least the each of at least some of the composite search keywords by the registration unit.