PageRank is one of the link ranking algorithms. This algorithm is applied to a collection of documents linked by the hyperlinks (such as web-sites of the World Wide Web), and assigns each of them a certain numeric value, measuring the “importance” or the “authority” among the other documents. Commonly speaking the algorithm may be applied not only to web-pages but also to any set of objects, linked with each other by the mutual links, i.e. to any graph.
In 1996 Sergey Brin and Larry Page, the postgraduates of Stanford University at that time, started their work at the RackRub project – the Internet search engine using the new idea that the importance of a web-page is as great as many other pages link toward it and as important these pages are themselves. In some time BackRub was renamed to Google. The first article with the description of the algorithm used in it, named as PageRank, appeared in 1998, and later the article describing the architecture of the search engine showed up. This system returned search results of much higher quality in comparison to other existing search engines of that time and when Brin and Page realized its potential they founded Google Inc. in September 1998 for the further development as a commercial product.
Since that time the algorithms and the mathematical models used for the ranking by Google were greatly improved. During the interview in 2007 the representative of the search quality department Amit Singhal, claimed that their search engine was using over 200 ranking signals and PageRank is only one of them, but it still plays a great role in search products of Google. We should consider that the PageRank algorithm introduced in the Page’s article in 1998 may be improved in some practical aspects (E.G. links can be given different weights) and the algorithms used in modern engines are more like modifications.
PageRank can be interpreted as a rank of a page but Google Inc. associate the word ‘Page’ not with the meaning of a traditional book page or a web-page but with the name of Larry Page.
“PageRank” is a registered trademark of Google Inc. The algorithm was patented in the USA in September 4 2001. Larry Page was signed as the algorithm inventor. The official owner of the patent is not Google Inc., but Stanford University where Larry Page and Sergey Brin studied at the moment of applying for a patent.
In 1998 Google was one of the first search engines introducing link ranking thanks to which it gained a significant raise of search quality unlike others. Later many other major search engines developed their analogues of PageRank and other ways of static (i.e. request-free) document ranking.
PageRank is a numeric value characterizing the “importance” of a web-page. The more links are pointing towards the page the more “important” it becomes. Moreover the ‘weight’ of the A page is defined by the weight of a link given by the page B. So PageRank is the way to define the weight of a page calculating the importance of the inbound links.
PageRank in Google products
The browser superstructure Google Toolbar shows a number from 1 to 10 for every web-page. It calls it PageRank or the importance of the page as for Google. But the mechanism of its calculation and the exact meaning of this value are hidden. Some think this value is updated once a several years (when the internal value of PageRank is recalculated all the time) and show the PageRank values in logarithmic scale.
The PageRank value (maybe together with some other factors) is also shown as a green stripe in the Google Directory site catalogue where they are used to sort the sites inside the catalogue.