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Google PageRank

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PageRank-hi-res

PageRank, sometimes abbreviated to PR, is a family of algorithms for assigning numerical weightings to hyperlinked documents (or web pages) indexed by a search engine originally developed by Larry Page (thus the play on the words PageRank). Its properties are much discussed by search engine optimization (SEO) experts. The PageRank system is used by the popular search engine Google to help determine a page’s relevance or importance. It was developed by Google’s founders Larry Page and Sergey Brin while at Stanford University in 1998. As Google puts it:

PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page’s value. Google interprets a link from page A to page B as a vote, by page A, for page B. But Google looks at more than the sheer volume of votes, or links a page receives; it also analyzes the page that casts the vote. Votes cast by pages that are themselves “important” weigh more heavily and help to make other pages “important.”

PageRank uses links as “votes”

In other words, a page rank results from a “ballot” among all the other pages on the World Wide Web about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it (“incoming links”). A page that is linked by many pages with high rank receives a high rank itself. If there are no links to a web page there is no support of this specific page.

In early 2005, Google implemented a new attribute, rel=”nofollow”, for the HTML link element, so that website builders and bloggers can make links that Google will not follow for the purposes of PageRank—they are links that no longer constitute a “vote” in the PageRank system. The nofollow attribute was added in an attempt to help combat comment spam.

The Google Toolbar PageRank goes from 0 to 10. It seems to be a logarithmic scale. The exact details of this scale are not public knowledge. The name PageRank is a trademark of Google. This is a pun on the name Larry Page. The PageRank process has been patented (U.S. Patent 6,285,999). The patent is not assigned to Google but to Stanford University.

An alternative to the Page rank algorithm is the HITS algorithm proposed by Jon Kleinberg and the CLEVER project at IBM. Many HITS concepts are now incorporated into Teoma and Ask Jeeves.

False or spoofed PageRank

While the PR shown is usually accurate for most sites it must be noted that it is also easily manipulated. A current flaw is that any low PageRank page that is redirected, via a 302 server header or a “Refresh” meta tag, to a high PR page causes the lower PR page to acquire the PR of the destination page. In theory a new, PR0 page with no incoming links can be redirected to the Google home page – which is a PR 10 – and by the next PageRank update the PR of the new page will be upgraded to a PR10. This is called spoofing and is a known failing or bug in the system. Any page’s PR can be spoofed to a higher or lower number of the webmaster’s choice and only Google has access to the real PR of the page.

Buying Text Links

For SEO purposes webmasters often buy links for their sites. As links from higher PR pages are believed to be more valuable they tend to be more expensive. It can be an effective and viable marketing strategy to buy link advertisements on content pages of quality & relevant sites to drive traffic & increase a webmasters link popularity.

Licensed under the GNU Free Documentation License. It uses materials from the Wikipedia.

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