6. The computer-implemented system according to claim 3 , wherein the first extraction unit further: collects the same noun words from the noun words Ki and sets the same noun words as a certain one of noun words Si (i=1, 2, . . . , k) (n≧k); assigns a weight to each of the noun words Si based on the weights assigned to the corresponding noun words Ki; and extracts the noun word Si assigned a weight equal to or greater than a predetermined threshold value.
6. The computer-implemented system according to claim 3 , wherein the first extraction unit further: collects the same noun words from the noun words Ki and sets the same noun words as a certain one of noun words Si (i=1, 2, . . . , k) (n≧k); assigns a weight to each of the noun words Si based on the weights assigned to the corresponding noun words Ki; and extracts the noun word Si assigned a weight equal to or greater than a predetermined threshold value. 7. The computer-implemented system according to claim 6 , wherein: the first extraction unit determines whether or not the weight of each noun word Si is in a predetermined threshold value range; and when the weight of the noun word Si is in the predetermined threshold value range, the first extraction unit determines whether or not a character type of the noun word Si is adequate as a term; when determining the character type as adequate, the first extraction unit sets the noun word Si as a noun word to be extracted; when determining the character type as inadequate, the first extraction unit sets the weight of the noun word Si to zero; and when the weight of the noun word Si is not in the predetermined threshold value range, the first extraction unit sets the weight of the noun word Si to zero.