9. An apparatus for identifying at least one unique character string in an input document which is input into a computer system, said computer system containing one or more documents which are searchably stored by the computer, the apparatus comprising: a storage device for storing a position information file which associates and manages position information for a position in said searchably stored documents where one or more partial comparison document character strings are extracted from said searchably stored documents; means for extracting a candidate character string from said input document; means for identifying a partial comparison document character string which matches part of said candidate character string with a predetermined similarity factor or higher; means for identifying position data which is associated to said partial comparison document character string having the predetermined similarity factor or higher in said position information file; and means for recognizing said candidate character string as the unique character string by comparing appearance frequency information of at least a part of said candidate character string appearing in said input document with said position information, and evaluating an amount of feature of said candidate character string.
9. An apparatus for identifying at least one unique character string in an input document which is input into a computer system, said computer system containing one or more documents which are searchably stored by the computer, the apparatus comprising: a storage device for storing a position information file which associates and manages position information for a position in said searchably stored documents where one or more partial comparison document character strings are extracted from said searchably stored documents; means for extracting a candidate character string from said input document; means for identifying a partial comparison document character string which matches part of said candidate character string with a predetermined similarity factor or higher; means for identifying position data which is associated to said partial comparison document character string having the predetermined similarity factor or higher in said position information file; and means for recognizing said candidate character string as the unique character string by comparing appearance frequency information of at least a part of said candidate character string appearing in said input document with said position information, and evaluating an amount of feature of said candidate character string. 10. The apparatus for identifying at least one unique character string in an input document according to claim 9, wherein in said means for recognizing the candidate string as the unique string, said amount of feature is a point allocation for said candidate character string and points are allocated according to the equation: ##EQU14## where: count i=appearance frequency of an i-th candidate character string in the input document; Ncount i j=appearance frequency of a j-th partial input character string of the i-th candidate character string in the input document; Nsize i j=position data corresponding to the j-th partial input character string of the i-th candidate character string; Nnum i=a number of partial input character strings contained in an i-th candidate character string; Max (Nsize i j)=maximum Nsize i j for all searchably stored documents; Max (Ncount i j)=maximum Ncount i j for all searchably stored documents.