As we’ll see, the trick is to ask the web itself to rank the importance of pages…
Imagine a library containing 25 billion documents but with no centralized organization and no librarians. In addition, anyone may add a document at any time without telling anyone. You may feel sure that one of the documents contained in the collection has a piece of information that is vitally important to you, and, being impatient like most of us, you’d like to find it in a matter of seconds. How would you go about doing it?
Posed in this way, the problem seems impossible. Yet this description is not too different from the World Wide Web, a huge, highly-disorganized collection of documents in many different formats. Of course, we’re all familiar with search engines (perhaps you found this article using one) so we know that there is a solution. This article will describe Google’s PageRank algorithm and how it returns pages from the web’s collection of 25 billion documents that match search criteria so well that “google” has become a widely used verb.
Most search engines, including Google, continually run an army of computer programs that retrieve pages from the web, index the words in each document, and store this information in an efficient format. Each time a user asks for a web search using a search phrase, such as “search engine,” the search engine determines all the pages on the web that contains the words in the search phrase. (Perhaps additional information such as the distance between the words “search” and “engine” will be noted as well.) Here is the problem: Google now claims to index 25 billion pages. Roughly 95% of the text in web pages is composed from a mere 10,000 words. This means that, for most searches, there will be a huge number of pages containing the words in the search phrase. What is needed is a means of ranking the importance of the pages that fit the search criteria so that the pages can be sorted with the most important pages at the top of the list… Continue reading ‘Secrets of Google’s PageRank algorithm.’
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