1. One or more non-transitory computer-readable storage media collectively storing computer-executable instructions that, when executed by one or more computer systems, configure the one or more computer systems to collectively perform operations comprising: determining at least a portion of a text string associated with an electronic book; determining one or more nouns in the text string; associating each of the one or more nouns with one or more characters so as to create a set of characters for the electronic book; determining one or more verbs in the text string, each of the one or more verbs representing an action between one of the characters of the set of characters and at least one other of the characters of the set of characters; generating a character graph that represents relationships between the one or more characters based at least in part upon the one or more verbs and the actions between the one or more characters, the one or more characters represented as nodes in the character graph; calculating a number of the nodes in the character graph; comparing the number of the nodes to a character threshold; and determining a maturity level of the electronic book based in part on the comparison of the character threshold with the number of the nodes in the character graph.