a plurality of input means for inputting different types of information;

conversion means for converting information input from any of said plurality of input means into a character string representing the information;

storage means for storing a plurality of character strings converted by said conversion means with an input time thereof;

sorting means for sorting the plurality of character strings stored in said storage means in an order of the input time;

a knowledge base for storing knowledge of each concept which includes a character string representing the concept, a concept type of the concept, a concept instance rule for defining a property of a concept instance to be filled in each slot provided for the concept in correspondence with a slot type of the slot, and a surface rule for defining an order of a character string representing the concept instance to be filled in each slot and a grammar of the character string representing the concept;

input concept instance generating means for generating a plurality of input concept instances corresponding to the plurality of character strings sorted in the input time order by said sorting means, by referring to the knowledge stored in said knowledge base;

request information list generating means for generating a request information list which includes, for each of the plurality of input concept instances, I) an instance request for filling respective slots with specified concept instances in accordance with the concept instance rule of the input concept instance, II) a surface request for obeying a specified order of character strings and a specific grammar in accordance with the surface rule of the input concept instance, and, III) a concept definition request which does not overlap with any existing requests in accordance with a different concept instance rule defined in a concept definition for the concept type of the input concept instance;

applicable request list generating means for generating an applicable request list by generating combinations each of which includes an applicable concept request in the request information list and a corresponding concept instance in the plurality of input concept instances, and excluding a combination which does not satisfy the surface request in the request information list and a combination which includes an applicable concept request competing with other requests from the generated combinations, included in the request list; and

concept instance unifying means for unifying the plurality of input concept instances by filling a slot of one of the input concept instances with another one of the input concept instances having a concept type which matches with the property of the concept instance for the slot by applying an applicable request in the applicable request list.