Keyword Search in Search Engines

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How do search engines execute a keyword search?

When you type in a keyword phrase to a search engine how does it retrieve the web pages that appear on the search engine results page?
When a user hits the submit button and a search is executed what actually happens? Below is a depiction of what happens when someone searches using Google.
 
1. User inputs search query
2. The web server sends the search query to the index servers. The servers will look at their index and decide which pages are the closest match for the search query
3. The query then travels to the doc servers. Here the stored documents are retrieved. Only a snippet of the document is retrieved to describe each search engine result.
4. The results are returned to the user in a matter of seconds. .

The really interesting question is what happens at the second stage of the process, when the index servers are deciding what is the closest match to the search query. How does the search engine calculate what to return.

It uses an algorithm, defined as 'a set of rules that a search engine uses to rank the listings contained within its index, in response to a particular query'. Of course it doesn't only use one algorithm, there are many that are applied before the results are returned.

What are the main factors they are contained in the Google algorithm? Although not a definitive answer, the following are broadly recognised to be important:
  • Title Tag
  • Anchor Text of Links
  • Keyword Use in Document Text
  • Accessibility of Document
  • Links to Document from Site-Internal Pages
  • Primary Subject Matter of Site
  • External Links to Linking Pages
  • Link Popularity of Site in Topical Community
  • Global Link Popularity of Site
  • Keyword Spamming

So, if you implement the factors above on your website, will you get a high ranking? The answer is probably, eventually. You can never be certain of a top ranking, as the search engines can change their algorithm at any time and they will not openly communicate to you what the changes were.

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