Nope, there was almost no mention of what this was actually used for. The closest I found was a mention of the final output:

"single output files, tab-delimited with data available for each year, merging in publication metadata and other information about each book"

[edit] More info in a link at the bottom of the article: http://blog.gdeltproject.org/3-5-million-books-1800-2015-gde...