1. A non-transitory computer readable medium having stored thereon a character string updated degree evaluation program allowing a computer to execute: an extraction step of extracting common part character strings each comprising successive plural characters and each having a length greater than or equal to an arbitrary threshold value from original and updated texts subjected to comparison with each other; a step of arranging the common part character strings in an order that the common part character strings occur in the respective texts, to create divided lines; and a step of comparing the divided lines with each other, calculating a minimum number of substitution among the common part character strings necessary to cause one divided line to match another divided line, thereby acquiring a context edit distance, comprising: a step of subtracting 1 from a number of extracted common part character strings to acquire an edited point number as a number of edited points where editing is performed; a step of calculating a rate of a total length of remaining character strings obtained by eliminating the common part character strings from the text with respect to a total length of that text; a step of collecting remaining character strings obtained by eliminating the common part character strings from each text to create a non-common part character string set, and a novelty degree evaluation step of acquiring a new creation novelty degree DO which is a non-matching rate of an N-gram in a length less than the threshold value among non-common part character string sets, wherein the new creation novelty degree DO is expressed by DO=1−|Γ 1 ∩Γ 2 |/| 1 | (where Γ 1 and Γ 2 are N-gram sets each created from a non-common part character string set, |Γ 1 ∩Γ 2 | is a number of common elements commonly occurring in the N-gram sets Γ 1 and Γ 2 , and |Γ 1 | is a total number of N-grams contained in the N-gram set Γ 1 ); and a step of calculating a character string updated degree from an evaluation equation: a·EP+b·CED+NCP·DO·L (where EP is a number of edited points, CED is a context edit distance, NCP is a new creation percentage, DO is a new creation novelty degree, L is a total length of an updated text, and a and b are arbitrary coefficients), using the number of edited points, the context edit distance, the new creation percentage, and the new creation novelty degree.
1. A non-transitory computer readable medium having stored thereon a character string updated degree evaluation program allowing a computer to execute: an extraction step of extracting common part character strings each comprising successive plural characters and each having a length greater than or equal to an arbitrary threshold value from original and updated texts subjected to comparison with each other; a step of arranging the common part character strings in an order that the common part character strings occur in the respective texts, to create divided lines; and a step of comparing the divided lines with each other, calculating a minimum number of substitution among the common part character strings necessary to cause one divided line to match another divided line, thereby acquiring a context edit distance, comprising: a step of subtracting 1 from a number of extracted common part character strings to acquire an edited point number as a number of edited points where editing is performed; a step of calculating a rate of a total length of remaining character strings obtained by eliminating the common part character strings from the text with respect to a total length of that text; a step of collecting remaining character strings obtained by eliminating the common part character strings from each text to create a non-common part character string set, and a novelty degree evaluation step of acquiring a new creation novelty degree DO which is a non-matching rate of an N-gram in a length less than the threshold value among non-common part character string sets, wherein the new creation novelty degree DO is expressed by DO=1−|Γ 1 ∩Γ 2 |/| 1 | (where Γ 1 and Γ 2 are N-gram sets each created from a non-common part character string set, |Γ 1 ∩Γ 2 | is a number of common elements commonly occurring in the N-gram sets Γ 1 and Γ 2 , and |Γ 1 | is a total number of N-grams contained in the N-gram set Γ 1 ); and a step of calculating a character string updated degree from an evaluation equation: a·EP+b·CED+NCP·DO·L (where EP is a number of edited points, CED is a context edit distance, NCP is a new creation percentage, DO is a new creation novelty degree, L is a total length of an updated text, and a and b are arbitrary coefficients), using the number of edited points, the context edit distance, the new creation percentage, and the new creation novelty degree. 4. The non-transitory computer readable medium having stored thereon the character string updated degree evaluation program according to claim 1 , wherein the extraction step comprises the steps of: coupling a first character string and a second character string, corresponding to respective original and updated texts, with a terminal symbol; creating a suffix array for a coupled character string to calculate a height array, and compares a numerical value of an index of a suffix with a character string length of the first character string which is a front part of the coupled character string, when the suffix array is created; dividing into a group that a starting part of a suffix begins with the first character string and a group that a starting part of a suffix begins with the second character string; and extracting a character string as a longest common part character string which matches at the beginning between adjoining suffix arrays from the text, wherein an adjoining suffix array is another group and corresponds to a position having a highest height; and repeating extracting a longest common part character string from remaining character strings until the length of the longest common part character string becomes less than or equal to the threshold value, wherein the extraction step replaces a common part character string with another special character when extracting the common part character string.