The job here is to screen scrape the subsidiary pages on the EDGAR database and translate them into an open format that will be published to the web and can be inputted into the Prefuse visualization software or another API.

The SEC's EDGAR website theoretically has lists of subsidiaries for all publicly traded companies in the USA. They are listed as "Exhibit 21" on forms S-1, S-4, S-11, F-1, F-4, 10, and the annual report filed on Form 10-K. Here are two examples:

http://www.sec.gov/Archives/edgar/data/831001/000119312507038505/dex2101.htm