Posting 3-Web search engine

Web search engine

A Web search engine is a tool designed to search for information on the World Wide Web. The search results are usually presented in a list and are commonly called hits. The information may consist of web pages, images, information and other types of files. Some search engines also mine data available in newsbooks, databases, or open directories. Unlike Web directories, which are maintained by human editors, search engines operate algorithmically or are a mixture of algorithmic and human input.

Web search engines work by storing information about many web pages, which they retrieve from the WWW itself. These pages are retrieved by a Web crawler (sometimes also known as a spider) — an automated Web browser which follows every link it sees. Exclusions can be made by the use of robots.txt. The contents of each page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). 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 source page (referred to as a cache) as well as information about the web pages, whereas others, such as AltaVista, store every word of every page they find. This cached page always holds the actual search text since it is the one that was 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 might be considered to be a mild form of linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be on the returned webpage. This satisfies the principle of least astonishment since the user normally expects the search terms to be on the returned 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 elsewhere.

When a user enters a query into a search engine (typically by using key words), the engine examines its index and provides a listing of best-matching web pages according to its 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 operators AND, OR and NOT to further specify the search query. Some search engines provide an advanced feature called proximity search which allows users to define the distance between keywords.

Taken from: http://www.blogger.com/www.wikipedia.org.

Mamma.com: Copernic Inc., originally called Mamma.com, launched in 1996 by Herman Tumurcuoglu, was one of the web's first metasearch engines. Its slogan is "The Mother Of All Search Engines". Its search engine cover the field of websites, jobs videos, shopping, travel, the yellow pages and the white pages.

Google Scholar: Google Scholar is a freely-accessible Web search engine that indexes the full text of scholarly literature across an array of publishing formats and disciplines. The Google Scholar index includes most peer-reviewed online journals of the world's largest scientific publishers. Its advertising slogan — "Stand on the shoulders of giants" is a nod to the scholars who have contributed to their fields over the centuries, providing the foundation for new intellectual achievements.

Eric digest: ERIC Digests are short reports (1,000 - 1,500 words) on topics of prime current interest in education. There are a large variety of topics covered including teaching, learning, libraries, charter schools, special education, higher education, home schooling, and many more

Yahoo.com: Yahoo! Search is a web search engine, owned by Yahoo!, Inc. and is currently the second largest search engine on the web, after its competitor Google. Yahoo! Search, originally referred to as Yahoo! provided Search interface, would send queries to a searchable index of pages supplemented with its directory of sites. The results were presented to the user under the Yahoo! brand.

Similarities

In my opinion the similarities between these search engines is that all of them uses a keyword to find what you are looking for. Another one is that all of them will display the results based on the keyword for what you are looking for. Also all of these search engines uses the same interface where you can insert the keyword.

Differences

In my opinion, the are a few differences between these search engines. The first one is that only google scholar and eric digests are based on academic research. This means that only these two seach engines focus on searching something academic related such as journals and academic articles. The second difference is that only mamma.com and yahoo.com has a link for searching videos and shopping. The next one is that, only mamma.com has a link to search the white pages. The last difference is that, all of these search engines have a different interface which makes them unique.