Web search engines work by storing information about many web pages, which they retrieve from the Web itself. Crawler-based search engines have three major elements. First is the spider, also called the crawler. The spider visits a web page, reads it, and then follows links to other pages within the site [1]. This is what it means when someone refers to a site being "spidered" or "crawled". The spider returns to the site on a regular basis, such as every month or two, to look for changes. Everything the spider finds goes into the second part of the search engine, the index. The index, sometimes called the catalogue, is like a giant book containing a copy of every web page that the spider finds. If a web page changes, then this book is updated with the new information. Sometimes it can take a while for new pages or changes that the spider finds to be added to the index. Thus, a web page may have been "spidered" but not yet "indexed". Until ...