9. A computer system for determining section information of a digital volume, the system comprising: a non-transitory computer-readable storage medium storing executable computer program modules comprising: a classifier module for determining pages of the digital volume containing a table of contents by applying a classifier to the digital volume, the classifier adapted to use machine learning to recognize references to sections in a body of the digital volume and identify pages of the digital volume containing the section references as the pages containing the table of contents; and generating a score estimating an accuracy of a classification of a page as containing the table of contents; a phrase extraction module for extracting phrases from the table of contents of the digital volume, the digital volume comprising a plurality of sections; a phrase matching module for identifying matching phrases in the body of the digital volume, the matching phrases at least approximately matching the extracted phrases; and a match selection module for: determining best matching phrases from the identified matching phrases, the best matching phrases comprising a matching phrase corresponding to each extracted phrase, the determining based at least in part on the ordering of the extracted phrases and the identified matching phrases; generating section information, the section information comprising section headings and section start locations, the section headings comprising the best matching phrases, and the section start locations indicating starting locations of the sections in the digital volume, the section start locations comprising the locations of the best matching phrases in the digital volume; and storing the section information; and a processor for executing the computer program modules stored in the computer-readable storage medium.
9. A computer system for determining section information of a digital volume, the system comprising: a non-transitory computer-readable storage medium storing executable computer program modules comprising: a classifier module for determining pages of the digital volume containing a table of contents by applying a classifier to the digital volume, the classifier adapted to use machine learning to recognize references to sections in a body of the digital volume and identify pages of the digital volume containing the section references as the pages containing the table of contents; and generating a score estimating an accuracy of a classification of a page as containing the table of contents; a phrase extraction module for extracting phrases from the table of contents of the digital volume, the digital volume comprising a plurality of sections; a phrase matching module for identifying matching phrases in the body of the digital volume, the matching phrases at least approximately matching the extracted phrases; and a match selection module for: determining best matching phrases from the identified matching phrases, the best matching phrases comprising a matching phrase corresponding to each extracted phrase, the determining based at least in part on the ordering of the extracted phrases and the identified matching phrases; generating section information, the section information comprising section headings and section start locations, the section headings comprising the best matching phrases, and the section start locations indicating starting locations of the sections in the digital volume, the section start locations comprising the locations of the best matching phrases in the digital volume; and storing the section information; and a processor for executing the computer program modules stored in the computer-readable storage medium. 10. The computer system of claim 9 , wherein identifying matching phrases in the body of the digital volume further comprises: indexing words of the digital volume to create a word index; identifying lookup words from the extracted phrases; looking up the lookup words in the word index to determine matching words, the matching words being exact or approximate matches of the lookup words; and identifying matching phrases in the body of the digital volume based at least in part on the matching words.