Tag Archives: search engine

Three Types of Search Engines

The term "search engine" is often used generically to describe crawler-based search engines, human-powered directories, and hybrid search engines. These types of search engines gather their listings in different ways, through

  1. crawler-based searches
  2. human-powered directories
  3. hybrid searches

1. Crawler-based search engines

Crawler-based search engines, such as Google (http://www.google.com), create their listings automatically. They "crawl" or "spider" the web, then people search through what they have found. If web pages are changed, crawler-based search engines eventually find these changes, and that can affect how those pages are listed. Page titles, body copy and other elements all play a role.

The life span of a typical web query normally lasts less than half a second, yet involves a number of different steps that must be completed before results can be delivered to a person seeking information. The following graphic (Figure 1) illustrates this life span (from http://www.google.com/corporate/tech.html):

  1. The web server sends the query to the index servers. The content inside the index servers is similar to the index in the back of a book – it tells which pages contain the words that match the query.
  2. The query travels to the doc servers, which actually retrieve the stored documents. Snippets are generated to describe each search result.
  3. The search results are returned to the user in a fraction of a second.

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