Definition
-Britannica Concise Encyclopedia
Tool for finding information, especially on the Internet or World Wide Web. Search engines are essentially massive databases that cover wide swaths of the Internet. Most consist of three parts: at least one program, called a spider, crawler, or bot, which "crawls" through the Internet gathering information; a database, which stores the gathered information; and a search tool, with which users search through the database by typing in keywords describing the information desired (usually at a Web site dedicated to the search engine).
Program that scans or "crawls" through Web pages, classifying and indexing them based on a set of pre-determined criteria.
Search engines help organize the more than two billion pages of information on the World Wide Web and make them accessible to Internet users. Search engines are the primary method Internet surfers use to locate information on the Web. In fact, Karl Greenberg noted in Brandweek that 85 percent of Internet surfers use search engines to locate information online. Search engines generate the largest percentage of new traffic to Web pages, followed by links from other sites, printed media, and word of mouth.
How to use Search Engine
-Keyword searching
This is the most common form of text search on the Web. Most search engines do their text query and retrieval using keywords. Keyword can simply be any word on a webpage. Words that are mentioned towards the beginning of a document are given more weight by most search engines. The same goes for words that are repeated several times throughout the document. Some search engines index every word on every page. Others index only part of the document. Full-text indexing systems generally pick up every word in the text except commonly occurring stop words such as "a", "an", "the", "is", "and", "or" and "www." Some of the search engines discriminate upper case from lower case; others store all words without reference to capitalization.
-Refining your search
Most sites offer two different types of searches--"basic" and "refined" or "advanced." In a "basic" search, just enter a keyword without sifting through any pull down menus of additional options. Depending on the engine, though, "basic" searches can be quite complex. Advanced search refining options differ from one search engine to another, but some of the possibilities include the ability to search on more than one word, to give more weight to one search term than you give to another, and to exclude words that might be likely to muddy the results. Some search engines also allow users to specify what form they'd like your results to appear in, and whether users wish to restrict their search to certain fields on the internet (i.e., usenet or the Web) or to specific parts of Web documents (i.e., the title or URL). Many, but not all search engines allow users to use so-called Boolean operators to refine your search. These are the logical terms AND, OR, NOT, and the so-called proximal locators, NEAR and FOLLOWED BY. Some search engines use the characters + and - instead of Boolean operators to include and exclude terms. The ability to query on phrases is very important in a search engine. Those that allow it usually require to enclose the phrase in quotation marks, i.e., "space the final frontier."
-Relevancy rankings
Most of the search engines return results with confidence or relevancy rankings. In other words, they list the hits according to how closely they think the results match the query. Most search engines use search term frequency as a primary way of determining whether a document is relevant. If you're researching diabetes and the word "diabetes" appears multiple times in a Web document, it's reasonable to assume that the document will contain useful information. Therefore, a document that repeats the word "diabetes" over and over is likely to turn up near the top of your list. If your keyword is a common one, or if it has multiple other meanings, you could end up with a lot of irrelevant hits. And if your keyword is a subject about which you desire information, you don't need to see it repeated over and over--it's the information about that word that you're interested in, not the word itself. Some search engines consider both the frequency and the positioning of keywords to determine relevancy, reasoning that if the keywords appear early in the document, or in the headers, this increases the likelihood that the document is on target.
References
1.http://www.answers.com/topic/search-engine
2.http://www.monash.com/spidap4.html
3.http://www.roanestate.edu/owl&writingcenter/OWL/researchguide.html
4.http://en.wikipedia.org/wiki/Search_engines
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