A web search engine is software which
searches the World Wide Web for the pages requested by the users based on
certain parameters which changes dynamically. The pages connected through
internet are indexed by the search engines and the results are returned in the
form of Search Engine Results Page (SERP).
The first tool used for searching on
the Internet was Archie.
The name Archie has been derived from the English word
archive meaning stored records. It was created in 1990 by Alan Emtage, Bill
Heelan and J. Peter Deutsch, computer science students at McGill University in
Montreal. The program downloaded the directory listings of all the files
located on public anonymous FTP (File Transfer Protocol) sites, creating a
database with can be searched for information. However, Archie did not create
an index for searching efficiently as the amount of data accessed was small.
According to the types of search methods
employed search engines can be categorized into:- 

  • Crawler based search engine
  •  Human powered search engine
  • Metadata based search engine
This type of search engines employ software
called web crawler or spider to search and retrieve information from the web
and prepare an index which contains a list of the popular keywords and the
location they are found. Web page changes can be dynamically caught by
crawler-based search engines and will affect how these web pages get listed in
the search results. A crawler based search engine starts with the most popular
websites and travel by following the links present on the website.
Human-powered search engines, also known as
Web directories, are popular because of the fact that they return higher
quality of links in response to the search request submitted and reliability of
the sites which are manually checked and added to the index only if found
suitable. Human powered search engines employ or involve multiple persons
searching multiple search engines, using multiple keywords and phrases,
searching multiple websites for links &
 information that are relevant and valid.
This technique is also sometimes called Social Searching or Human Power. Humans
are always more reliable than machines when it comes to categorizing and organizing
information and knowledge.

Meta-search engines
A search engine that queries multiple search engines
combines the results that are retrieved from all and returns a summary report
to the client. In effect, the user is not using just one search engine but a
combination of many search engines for optimized and efficient Web searching.
Therefore, the search results you receive are an aggregate result of multiple
searches. While this strategy gives your search a broader scope than searching
a single search engine, the results are not always better.  For example, Dogpile is a Meta search engine.

Meta search engine must use its own algorithm
to choose the best results from multiple search engines. These search engines
do not have their own databases and they do not index sites or compile their
own databases; instead they are programmed to send multiple requests to the top
search engines simultaneously.



Indrani Sen is a teacher,lecturer in Information Technology/Computer Science for the past 12 years. She has authored 4 text books in Information Technology.
She is passionate about cooking and loves to blog about food and travel.This blog is like my baby as I have built it from scratch by myself with little help from colleagues ,friends and of course Google.


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