1. An information processing apparatus comprising: a title acquiring unit acquiring a title character string showing a title of content; a title analyzing unit analyzing the title character string acquired by the title acquiring unit and dividing the title character string into a plurality of tokens; an evaluation value calculating unit calculating, for each of the plurality of tokens, an evaluation value that is based on a character string length of the token and is weighted in accordance with a position of the token in the title character string; a mapping unit mapping, for each of the plurality of tokens, a token point, whose position is shown by a value of an ordinal number showing the position of the token in the title character string and the evaluation value, onto a coordinate plane; an extraction criterion deciding unit deciding, based on coordinates of the token points mapped onto the coordinate plane by the mapping unit, coordinates of a criterion point used as a criterion for extracting an identifier that identifies a series from the title and an extraction criterion based on the criterion point; an extracting unit extracting token points that conform to the extraction criterion out of the token points; and an identifier generating unit generating the identifier from the character strings included in tokens associated with the token points extracted by the extracting unit.