Declassified Documents Reference System is now called U.S. Declassified Documents Online. The resource has a new interface, additional search and annotation features, and additional content that includes selected records up to 2008.
A new feature allows you to graph either the frequency of your search term (the number of documents per year in which it appears) or its popularity (the percent of the total documents each year in which it appears). This of course only reflects the frequency or popularity of the term in the universe of documents that are contained in this database, which is not a comprehensive collection of declassified documents.