A search engine operates in the following order: 1) tracking, 2) Deep Crawling Depth-first search (DFS), 3) fresh Tracking breadth-first search (BFS), 4) index, 5) Search.
Search engines work by storing information about a large number of web pages that are retrieved from the WWW itself. These pages are retrieved by a web crawler (also known as spider) - an automated Web browser which follows every link it sees, exclusions can be made through the use of robots.txt. The content of each page is analyzed to determine how they should be indexed. Data about web pages is stored in an index database for use in subsequent queries. Some search engines such as Google, store all or any part of the site of origin (hereinafter, a cache) as well as information on web pages, while some store every word of every page it finds, such as AltaVista . This cached page always holds the actual search text since it is actually indexed, so it can be very useful when the content of the current page has been updated and the search terms are no longer in her . This problem can be considered a mild form of linkrot, and Google's handling of the increased ease of use to meet user expectations of search terms on the website will be returned. This satisfies the principle of least astonishment since the user normally expects the search terms in the pages returned. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may be unavailable elsewhere.
When a user enters the search engine and make a query, typically by giving keywords, the engine searches the index and provides a list of web pages better game according to its criteria, usually with a brief summary contains the document's title and sometimes parts of the text. Most search engines support the use of Boolean terms AND, OR and NOT to further specify the search. In an advanced search function of proximity, which allows you to define the distance between keywords.
The usefulness of a search engine depends on the relevance of the results it gives back. While there may be millions of Web pages that include a particular word or phrase, some pages may be more relevant, popular, or authoritative than others. Most search engines employ methods to rank the results for the "best" first results. How a search engine decides which pages are the best matches, and in what order the results should be shown in, varies widely from one engine to another. The methods also change over time as Internet usage changes and new techniques evolve.
Most search engines web commercial enterprises supported by advertising revenue and as a result, some employ the controversial practice of allowing advertisers to pay money to have their lists ranked higher on the results of search.
Most search engines are run by private companies using proprietary algorithms and closed databases, currently the most popular on Google, MSN Search and Yahoo! Search. However, the open source search engine technology does not exist, as ht: / / Dig, Nutch, Signs, Egothor, OpenFTS, DataparkSearch and many others.
December 09, 2009, 07:21:41 AM