Friday, October 29, 2010

How Does A Search Engine Work?

How it works
Though the workings of different search engines vary from each other, they all perform some basic functions. Essentially, all search engines work in an orderly fashion, performing three main operations -Web crawling, indexing and searching.
Web cmwflng: Before it can give you the information you want, a search engine has to find the information you are looking for. To find that information, search engines, which are basically webpages that respond to search queries, "crawl" the Web. Web crawling or spidering is one of the basic functions of a search engine. Spidering is achieved by retrieving stored information from webpages by means of a bot, referred to as a Web crawler or spider. A Web crawler is a computer program that navigates the internet in an automated, organised manner and retrieves the information directly from the page itself. It makes a copy of every link on each website visited, and analyses the content for indexing. Websites and URLs are not the only entries that spiders identify, they also take note of words within pages and where they were found, though means and techniques could vary from search engine to search engine.
Indexing: Once the spiders have collected all the information, it needs to be stored, compiled and organised so that it is accessible for users and available for searching. To be more than a website that lists links, search engines often store additional information including the frequency of the occurrence of words on a page, and the importance given to them (for rankings). Some engines also assign "weight" to each entry - measuring the differing value of words as they appear on a certain page. The entire information is then compacted and stored - ready for indexing. The most efficient means of building an index is by creating a hash table, which assigns a formula to the numeric value of each word, and consists of a hash number and a pointer to the actual data This arrangement makes the indexing and storage system effective for quick search results - even in cases of a complicated search.
Searching: This process is the first instance of the user's interaction with the search engine. Step one, build a query; step two, submit it. Once the query is submitted, it is processed by the search engine, which then extracts the information from the index.

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