In September 2008, Google News promoted an undated article about United Airlines' near bankruptcy in 2002. In the ensuing panic, the share price of United Airlines dropped by around 75% in a few hours. This problem was due in part to the fact that the article lacked provenance that readers could have used to determine that it was out of date. In an increasingly networked world, understanding of provenance is essential for establishing trust in data stored in databases and exchanged among Web sites. It is also critical to the process of making key business, scientific, and governmental...