Search engine in the operating sequence is as follows:
1) Crawling,
2) Deep Crawling Depth-first search (DFS),
3) Crawling Fresh Breadth-first (BFS);
4) Indexing,
5) search.
Search engines work by storing information about many web pages, they took from the WWW itself. These pages are retrieved by a web crawler (also known as a spider) - an automated web browser which follows every link it sees, an exception can be made using robots.txt. The contents of each page and then analyzed to determine how it should be indexed. Data about web pages are stored in an index database for use in later queries. Some search engines such as Google, store all or part of the page source (called a cache) as well as information on the web page, whereas some store every word of every page it finds, such as AltaVista.
Cached page always holds the actual search text since it is one that 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 it. This problem may be regarded as a mild form linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be returned web page. This satisfies the principle of least surprise since the user normally expects the search terms in the back pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available anywhere else.
When a user comes to search engines and create a query, typically by giving key words, the engine looks up the index and provides a list of best-matching web pages according to the criteria, usually with a short summary containing the document's title and sometimes parts of the text. Most search engines support the use of the boolean terms AND, OR and NOT to further specify the search query. An advanced feature is proximity search which allows you to specify the distance between keywords.
The usefulness of search engines depends on the relevance of results to return. Although there may be millions of web pages that contain 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 to provide the "best" results first. How does the search engine decides which pages are most suitable, and what order the results should be shown in, varies widely from one machine to another. The methods also change over time as Internet usage changes and new techniques evolve.
Most Web search engines are commercial ventures supported by advertising revenue and, as a result, some employ the controversial practice of allowing advertisers to pay money to have their listings ranked higher in search results.
Most search engines are run by private companies using proprietary algorithms and closed databases, the most popular currently being Google, MSN Search, and Yahoo! Search. However, Open source search engine technology does exist, such as Dig, Nutch, Senas, Egothor, OpenFTS, DataparkSearch and many others.
Cached page always holds the actual search text since it is one that 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 it. This problem may be regarded as a mild form linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be returned web page. This satisfies the principle of least surprise since the user normally expects the search terms in the back pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available anywhere else.
When a user comes to search engines and create a query, typically by giving key words, the engine looks up the index and provides a list of best-matching web pages according to the criteria, usually with a short summary containing the document's title and sometimes parts of the text. Most search engines support the use of the boolean terms AND, OR and NOT to further specify the search query. An advanced feature is proximity search which allows you to specify the distance between keywords.
The usefulness of search engines depends on the relevance of results to return. Although there may be millions of web pages that contain 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 to provide the "best" results first. How does the search engine decides which pages are most suitable, and what order the results should be shown in, varies widely from one machine to another. The methods also change over time as Internet usage changes and new techniques evolve.
Most Web search engines are commercial ventures supported by advertising revenue and, as a result, some employ the controversial practice of allowing advertisers to pay money to have their listings ranked higher in search results.
Most search engines are run by private companies using proprietary algorithms and closed databases, the most popular currently being Google, MSN Search, and Yahoo! Search. However, Open source search engine technology does exist, such as Dig, Nutch, Senas, Egothor, OpenFTS, DataparkSearch and many others.
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