Search Engines and Its Types PDF

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Summary

It describes what is a search engine, popular search engine, web directory, working of search engine, tyoes of search engine-meta search engine and its working...

Description

SEARCH ENGINE A search engine is a search tool that allows web users to search for information on World Wide Web (www). A user enters queries into a search engine and is provided with a list of results in the form of websites, webpages, videos, images or other web content. The list of results that a search engine returns is called search engine result page (SERP). POPULAR SEARCH ENGINES (top 5 search engine according to popularity) 1. 2. 3. 4. 5.

Google.com Bing.com Yahoo.com Ask.com AOL.com

WEB DIRECTORY A web directory or link directory is a catalogue of websites collected and organised by humans. A web directory is also called subject tree because it starts with few main categories and then branch into subcategories, topics and subtopics. Example-: if you want to search wakeboard you will have to follow: Home>Sports>All sports>Sports A-Z>Sports W-Z>Wakeboard Web directories may be general in scope (general-purpose web directory), or limited to particular subjects or fields (specialised web directory). For instance, DMOZ, Yahoo! Directory, The Best of the Web and Jasmine Directory are some general purpose web directories. Specialised web directories include the The Environment Directory which lists links to environmental sites only, and The Radio Directory which lists thousands of radio stations worldwide. Entries may be listed for free, or by paid submission (meaning the site owner must pay to have his or her website listed).

DIFFERENCE BETWEEN WEB DIRECTORY AND SEARCH ENGINE Web directories are human powered. Search engines differ from directories in that they are not compiled and maintained by humans. Instead, crawler-based search engines use sophisticated pieces of software called spiders or robots to search and index web pages.

WORKING OF SEARCH ENGINE:

1. Searching: A searcher is a program that accepts user’s query and uses the search engine’s database to provide a listing of best matching and most relevant websites using highly efficient search and sorting strategies. It uses two different search methods:

a. Breadth- first search: In breadth-first search, traversing occur layer wise i.e. all the nodes present in a layer (level) are traversed first before moving to next layer.

b. Depth-first search: In depth-first search, nodes of left sub tree(s) are traversed first, and then nodes of right sub tree(s) are traversed.

2. Web crawling: A web crawler, also called a spider, a robot, a worm, an ant or an automated indexer, is an automated bit of code that browses World Wide Web (www) in a systematic manner. This process is called web crawling or web spidering. Example, Xenon is a web crawler used by government tax authorities to detect fraud. Xapian, a search crawler engine, written in C++. 3. Web indexing: A web indexer is responsible for organising and sorting various websites collected by the crawler and maintaining an index for it. The purpose of indexing is to facilitate fast and accurate retrieval of web sites. 4. Ranking: Search engine uses complex ranking algorithm to decide which pages to show in the SERPS and in what order, when someone types a query. Example, PageRank (PR) is an algorithm used by Google Search to rank websites in their search engine results. TYPES OF SEARCH ENGINES: 1. Crawler based search engine like Google, yahoo, Bing 2. Human powered directories (web directories) like yahoo directory 3. Hybrid search engine ( combination of crawler based and web directory based search engine) like yahoo and bing 4. meta search engine like metacrawler and dogpile 5. speciality search engine (topical search engine) like FlipKart

META SEARCH ENGINE Meta search engine is a search tool that takes input (query) from a user and simultaneously sends out to several other search engines. Meta search engine combines the results obtained from different search engines into a single list and displays them to the user. Meta search engines are called aggregator because they aggregate the results obtained by several search engine.

Popular Meta search engines: 1.

2.

3.

DOGPILE (www.dogpile.com): Dogpile is a Meta search engine that attempts to deliver a better search experience by fetching results from numerous search engines including Google, Yahoo and Yandex. METACRAWLER (www.metacrawler.com): It is the meta-search engine that collects information from the top rated search engines like Google, Yahoo, Bing, Ask.com, MIVA, LookSmart and others. SPUTRR ( www.sputtr.com ): Sputrr fetches results from different search engines and websites like Google Image search, Google Web Search, YouTube, Dailymotion, Google News, Facebook, Twitter, IMDb, Slashdot, About.com, New York Times

4.

5.

INFO (www.info.com): Info.com is a meta search engine which provides results from leading search engines and pay-per-click directories, including Google, Yahoo!, Bing.com, Ask, LookSmart, About and Open Directory. IxQuik (www.startpage.com ): it is a Meta search engine which uses platforms like Exalead, Qkport, Ask, Gigablast, Wikipedia, Bebo, MSN, Winzy, CNN, NBC, Yahoo, EntireWeb, OPD. Ixquick now redirects users to startpage.com. WORKING OF META-SEARCH ENGINE:

User input a query into search engine. Broker simultaneously sends out query to several search engines. Search engines perform web crawling to gather results from World Wide Web. Then they use web indexer to index the collected webpages. All the results from different search engine are gathered by broker. Once all documents are retrieved the Meta search engine ranks them consistently in order to identify the best matching and most relevant websites. These websites are presented to the user in decreasing order of their global ranking....