11. A non-transitory computer readable recording medium that stores an information search program which causes an information search 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, to perform a 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.
11. A non-transitory computer readable recording medium that stores an information search program which causes an information search 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, to perform a 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. 12. The non-transitory computer readable recording medium as claimed in claim 11 , wherein the similarity calculation unit calculates the degree of similarity sim(Q, d) between the character string and the document d by sim ⁡ ( Q , d ) = ∑ k = 0 n ⁢ ⁢ score ⁡ ( Q , d , k ) wherein n indicates a predetermined value equal to or greater than 0.