How does a Search Engine Work?

Search engines perform several activities in order to deliver search results.

· Crawling - Process of fetching all the web pages linked to a website. This task is

performed by a software called a crawler or a spider (or Googlebot, in case of

Google).

· Indexing - Process of creating index for all the fetched web pages and keeping

them into a giant database from where it can later be retrieved. Essentially, the

process of indexing is identifying the words and expressions that best describe the

page and assigning the page to particular keywords.

· Processing - When a search request comes, the search engine processes it, i.e.,

it compares the search string in the search request with the indexed pages in the

database.

· Calculating Relevancy - It is likely that more than one page contains the search

string, so the search engine starts calculating the relevancy of each of the pages

in its index to the search string.

· Retrieving Results - The last step in search engine activities is retrieving the best

matched results. Basically, it is nothing more than simply displaying them in the

browser.

Search engines such as Google and Yahoo! often update their relevancy algorithm dozens

of times per month. When you see changes in your rankings, it is due to an algorithmic

shift or something else beyond your control.

Although the basic principle of operation of all search engines is the same, the minor

differences between their relevancy algorithms lead to major changes in the relevancy of

results.