Search engine optimization-Page Rank
Tuesday, July 15th, 2008Search engine ranking algorithms are closely guarded secrets, for at least two reasons: search engine companies want to protect their methods from their competitors, and they also want to make it difficult for web site owners to manipulate their rankings.
That said, a specific page’s relevance ranking for a specific query currently depends on three factors:
* Its relevance to the words and concepts in the query
* Its overall link popularity
* Whether or not it is being penalized for excessive search engine optimization (SEO).
Examples of SEO abuse would be a lot of sites linked to each other in a circular scam, or excessive and highly ungrammatical stuffing with keywords.
Factor 2 was innovated by Google with PageRank. Essentially, the more incoming links your page has, the better. But it is more complicated than that: indeed, PageRank is a tricky concept because it is circular, as follows: Every page on the Internet has a minimum PageRank score just for existing. 85% (at least, that’s the best known estimate, based on an early paper) of this PageRank is passed along to the pages that page links to, divided more or less equally along its outgoing links. A page’s PageRank is the sum of the minimum value plus all the PageRank passed to it via incoming links.
Although this is circular, mathematical algorithms exist for calculating it iteratively.
In one final complication, what I just said applies to “raw PageRank.” Google actually reports PageRank scores of 0 to 10 that are believed to be based on the logarithm of raw PageRank (they’re reported as whole numbers). And the base of that logarithm is believed to be approximately 6.
Anyhow, there are about 30 sites on the Web of PageRank10, including Yahoo, Google, Microsoft, Intel, and NASA. IBM, AOL, and CNN, by way of contrast, were only at PageRank 9 as of early in 2004.
Further refinements in link popularity rankings are under development. Notably, link popularity can be made specific to a subject or category; i.e., pages can have different PageRanks for health vs. sports vs. computers vs. whatever. Supposedly, AskJeeves/Teoma already works that way.
It is believed that Inktomi, Altavista, et al. use link popularity in their ranking algorithms, but to a much lesser extent than Google. Yahoo, owner of Inktomi, Altavista, Alltheweb, is rolling out a new search engine, which reportedly includes a feature called Web Rank. More on how that works soon.