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About Search Engines
Search engine searches for information available on the World Wide Web. The search engine actually searches a database of web pages that have been harvested and cached so the hits that you see could be based on an older version of the web page. The actual web page way have been updated since the page was cached and the update page may not contain the search word(s). This problem might be considered to be a mild form of linkrot. When you click on links in a search engine's results, you retrieve the current version of the page.
The information may consist of web pages, images, information and other types of files. Some search engines mine data and the results is available in databases or open directories. Unlike Web directories, search engines operate algorithmically or are a mixture of algorithmic and human input.
The very first tool used for searching on the Internet was created in 1990 and was called Archie which stands for "archive" without the "v."
Harvesting
Search engines work by storing information about many web pages, which they retrieve from the html itself. These pages are retrieved by a Web crawler, robot or spider. If a web page is never linked from any other page, web crawlers cannot find it. The only way a brand new page can get into a search engine is for other pages to link to it, or for a human to submit its URL for inclusion. All major search engines offer ways to do this. Exclusions can be made by the use of robots.txt.
Indexing
After a web crawler finds a web page, the contents of the page is analyzed to determine how it should be indexed. Words are extracted from the titles, headings, special fields called meta tags, text and links. Data about web pages are stored in an index database for use in later queries. Web pages can be excluded from search engines by policy.
Some search engines like Google, cache all or part of the source page and other information about the web pages.
AltaVista and others, cache every word of every page they find.
Searching
The user enters a query or list of key words into a search engine. The engine examines its index looking for the words or phrases exactly as entered. The search engine provides a listing of best-matching web pages according to its ranking criteria. Unfortunately, no search engine allow to search documents by date..
Ranking
Search engine rank web pages based on relevance criteria to determine the best matches and the order of the results. The method that search engines use to determine that some pages may be more relevant, popular, or authoritative than others varies widely from one engine to another and the methods may change over time as Internet usage changes and new techniques evolve. These are some items to consider:
- Emphasizing pages most heavily linked from other pages.
- Examine the entire link structure of the web and determine which pages are most important.
- Analyze full content of a page and factor in fonts, subdivisions and the precise location of each word.
- Analyze the content of neighboring web pages to ensure the results returned are the most relevant to a user's query.
Paid Inclusion
Most search engines either allow paid advertising or have search related ads alongside the regular search engine results. The search engines make money every time someone clicks on one of these ads.
There are many different search engines. Each search engine may give different results when you search. This is a list of some of the general search engines. Some of the main search engines are used by other search engines.
Meta-search Engine
Meta-search engine is a search tool that sends your search simultaneously to several individual search engine's index databases or catalogues and compile the results in to a list so you get results from all the search engines queried. Meta-search engines do not own a index database of web pages but create a virtual database from the databases maintained by search engine companies.
- General Search Engines - and the search engines that are based on the primary search engine
- Meta-search Engines
- Enterprise Search Engine
Page last updated: May 31, 2012 10:30 AM
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