6. An information search method in an apparatus for obtaining a character string from a client, obtaining information that includes the character string from an index database (DB), calculating degree of similarity between the character string and searched information, and outputting the searched information in descending order of the degree of similarity, wherein the index DB stores each word with sentence-based occurrence position information, of each document where the word occurs, that indicates each position of sentences where the word occurs, and the information search method comprising: a character string information search step in which, when the input character string contains a plurality of words, a character string information search unit searches the index DB, based on each word, to obtain a document d including each word and occurrence positions of each word in the document d, and a step in which a similarity calculation unit calculates a degree of agreement score(Q,d,k) between occurrence positions of the words by score ( Q , d , k ) ⁢ ∑ q i ∈ Q ⁢ ⁢ ∑ q j ∈ ( Q - q i ) ⁢ ⁢ 1 α ⁢ ⁢ k + 1 ⁢ count ⁡ ( Pos d ⁡ ( q i ) , Pos d k ⁡ ( q j ) ) so as to calculate the degree of similarity based on the degree of agreement score (Q,d,k), wherein Q indicates a set of words obtained by dividing the character string, Pos d (q i ) indicates an occurrence position of a word q i in the document d, Pos dk (q i ) indicates a value obtained by subtracting k from an occurrence position of a word q i in the document d, k indicates a counter value, α indicates a coefficient, and Count (Pos,Pos) indicates a function for receiving two pieces of position data and returning a degree of agreement.
6. An information search method in an apparatus for obtaining a character string from a client, obtaining information that includes the character string from an index database (DB), calculating degree of similarity between the character string and searched information, and outputting the searched information in descending order of the degree of similarity, wherein the index DB stores each word with sentence-based occurrence position information, of each document where the word occurs, that indicates each position of sentences where the word occurs, and the information search method comprising: a character string information search step in which, when the input character string contains a plurality of words, a character string information search unit searches the index DB, based on each word, to obtain a document d including each word and occurrence positions of each word in the document d, and a step in which a similarity calculation unit calculates a degree of agreement score(Q,d,k) between occurrence positions of the words by score ( Q , d , k ) ⁢ ∑ q i ∈ Q ⁢ ⁢ ∑ q j ∈ ( Q - q i ) ⁢ ⁢ 1 α ⁢ ⁢ k + 1 ⁢ count ⁡ ( Pos d ⁡ ( q i ) , Pos d k ⁡ ( q j ) ) so as to calculate the degree of similarity based on the degree of agreement score (Q,d,k), wherein Q indicates a set of words obtained by dividing the character string, Pos d (q i ) indicates an occurrence position of a word q i in the document d, Pos dk (q i ) indicates a value obtained by subtracting k from an occurrence position of a word q i in the document d, k indicates a counter value, α indicates a coefficient, and Count (Pos,Pos) indicates a function for receiving two pieces of position data and returning a degree of agreement. 9. The information search method as claimed in claim 6 , wherein, in the character string information search step, when the index DB stores sentence-based occurrence position information of each word, the character string information search unit searches the index DB based on a plurality of words obtained from the input character string, detects an ID of a sentence in which the plurality of words exist, and searches a document storing DB for the sentence corresponding to the ID, and, outputs the search result to the similarity calculation unit only when the sentence includes the input character string.