I was testing the Piwik web statistics application. What is supprise to me is that this app can tell if the entry to the certian page is a "direct entry" or entry from some other website.
How does it work? How does the Piwki app obtains this information?
Ultimately, it looks at the Referer HTTP header.
More specifically, the Javascript tracker sends two parameters: url and urlref. The url is always the current page, and urlref will be the previous page if there was a previous page. urlref might be an external page (hence Piwik's knowledge of search referrers and other sites), or it might be another page on the same site (which I assume Piwik uses for its pathing information).