A search engine represents a program that searches documents for keywords and creates a list of documents where these keywords are found. The term refers to all kinds of programs but it is commonly used to describe systems that allow users to search for documents and files on the Internet. In the 21st century, search engines allow users to search information for all kinds of topics in millions of pages.
The way search engines usually work is simple. They send out programs, called spiders, which automatically fetch web pages. The aim of these programs is to bring as many documents as they can find. There is another program — the indexer — that creates an index based on the words in each gathered document. Different search engines use different algorithms for these indices. The goal of the indexing process is to return only meaningful and relevant results for each query.
There are two main types of search engines. These include major search engines such as Google, which are also referred to as mega-marts on the web. The second kind of search engine includes databases that have a narrower scope. Among the most popular mega-marts are Google, Yahoo, Ask, AllTheWeb.com, AOL Search and HotBot. Of these search engines, Google and Yahoo are probably the most popular ones.
Google provides comprehensive coverage of the web and is also known for the many additional features it offers. It allows its users to search for images, to locate news information or to perform product searching. This search engine, which was originally called BackRub, started as a university project run by students Larry Page and Sergey Brin.
Yahoo, which was introduced in 1994, is defined as the oldest directory on the web. Later it changed to crawler-based listings for its main results, although there are notice category links below some of the sites listed in response to a keyword search. It is still possible to do a pure search of the Yahoo Directory, which is how the old Yahoo used to work. At present, Yahoo uses its own search technology. Other search engines that can be defined as major ones, although not in the leading positions such as Google and Yahoo, include AltaVista, Gigablast, Live Search, LookSmart, Lycos and Netscape Search.
Unlike major search engines, specialized search engines allow the user to get "on-topic" information. They are usually focused on a specific subject, geographic region or even a computer file format. Specialized search engines index a fewer number of Web pages and filter information that is not useful for a specific topic. There are specialized search engines for many categories, such as healthcare, media, science and law. There are also search engines that assist in finding a specialized search engine.
Specific search engines have a number of advantages. They often employ specialists to rank and annotate each link, thus providing higher quality. They can also save an individual's time thanks to their narrow focus. Specialized search entries choose their search engine entries and gather useful sites from user submission and not through the conventional robot process. Thus some entries may be unique to the specialized search engine.
Every search engine, no matter if major or specialized, is organized in its own way. However, there are several common features that make it easy for users to find what they are looking for. One of these features is phrase searching. In most search engines an individual can indicate a phrase by putting it in quotes. There are search engines where a person can choose the phrase option from a pull-down window. Using "and," "or" and "not" to specify a search is also a common feature of search engines and usually leads to more relevant results.
Other options provided by some search engines include proximity options, specified within 10, 25 or more words; directory attached indicator and search by date or relevance and search by language. Media searching is also available in some search engines. It provides an option to search by type of media such as audio and video file. Case sensitivity of the search engine, also a common feature, allows a person to easily distinguish "AIDS" from "aids" for example, while searching for information.