The URL Watcher program will poll registered URLs periodically to see if the page is changed, moved, or dead. Alternatively, web masters will have the ability to bypass the polling mechanism, and inform URL Watcher of a change directly. It becomes increasingly difficult to manage web-page information as the web quickly grows. When users identify important URLs, they often need to check the URLs frequently to see if the content has changed. Usually the pages are unchanged, but when they do change, the modifications are often missed.
Email is the classic and the most popular method of information push.
The web information providers look for new information for users and email the results to them. This might become unwieldy for a large number of pages, so users should have the option to make a manual, or regularly scheduled check of all important pages. They implemented it by web robot technology. The web robot downloads the content of the URL periodically, and compares the current one with the previous one that was downloaded the last time. If there is something changed, they will email to the users who registered the URLs.