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How search engines work?

This article explains how search engines work so that you can optimize your site for various search engines.

Each search engine have a database of all web sites in the world they know of. When you search for any term in search engines like Google, yahoo or MSN, they actually search in their database and show the results from their database.

Search engines continuously look for web pages and keep adding them to their database. This process is called "indexing". During indexing, the search engines will identify the major keywords in the web page and give a ranking for the web page for these keywords. Each web page indexed by the search engines will have different rankings for different keywords in the page.

When people search for these keywords, search engines display the results, sorted by this ranking.

A site can appear in the search results only if they are first saved into the database of the search engine.

How search engines find web sites ?

Search engines start with a single web page. This is an automated program which download the content of the page without even being noticed by anybody. When the search engine visit a web page, the following things happen:

1. Download the text content of the web page (Most search engines ignore the images and javascript in the page)

2. Analyze the content. Most search engines are smart enough to analyze the quality of the content and verify the grammar, spelling etc. Also, they look for duplicate content. If the content of your web is copied from other reputed web sites, your site may be ignored or may even black listed by search engines.

3. Parse the keywords. Search engines will identify the major keywords in your site and rank the page for various keywords, relative to other sites with the same keywords. For example, if your page talk about 'weather forecast', search engines will index your page for that keyword and give appropriate ranking compared to other sites with the same keywords. If your page get very high rank for this keyword, then when somebody search for 'weather forecast, your page will appear in the top few search results. Search engines consider several factors while giving the rank for each keyword. keyword optimization is discussed in detail in another chapter.

4. Save the keyword index and page content - search engines save the keyword ranking and page content in their database so that when users search for any keywords, they search in their index and show the results in a fraction of seconds.

5. Parse the hyperlinks in the content and visit the linked page - while parsing the content of any web page, search engines identify all the hyperlinks in that page to other pages and other sites. After completing the processing of the page, it will go to the pages linked from this page and repeat all the steps above for that page.

The above process continues for ever and search engines continue to download the pages and all the pages linked from each page continuously. The automatic download and parsing is done by some tools that is usually known as "search engine spider".

If you read carefully, you would have understood that your web site pages will be indexed by search engines if they are linked by other web sites. The more links you have from other web sites, the more chances you have getting indexed by search engines.

In addition to automatically finding web pages in the internet, most search engines allow submitting URLs directly to their list of sites to be indexed. They provide options to submit one or more URLs. Search engine submission is discussed in more detail later.

Next Chapter: Major Search Engines
Previous Chapter: Promote your web site with the help of friends
More Chapters: Search Engine Optimization Tutorials
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