The World Wide Web is the largest collection of data today and it continues increasing day by day. A web crawler is a program from the huge downloading of web pages from World Wide Web and this process is called Web crawling. To collect the web pages from www a search engine uses web crawler and the web crawler collects this by web crawling. Due to limitations of network bandwidth, time-consuming and hardware’s a Web crawler cannot download all the pages, it is important to select the most important ones as early as possible during the crawling process and avoid downloading and visiting many irrelevant pages. This paper reviews help the researches on web crawling methods used for searching.
Web crawler, Web Crawling Algorithms, Search Engine
A web crawler or spider is a computer program that browses the WWW in sequencing and automated manner. A crawler that is sometimes referred to as a spider, bot, or agent is software whose purpose is performed web crawling. The basic architecture of the web crawler is given below (Figure1). More than 13% of the traffic to a web site is generated by web search . Today the size of the web is thousands of millions of web pages that are too high and the growth rate of web pages is also too high i.e. increasing exponentially due to this the main problem for the search engine is to deal with this amount of the size of the web. Due to this large size of web induces low coverage and search engine indexing not cover one-third of the publicly available web .
By analyzing various log files of different web site they found that maximum web request is generated by a web crawler and it is on an average 50% . Crawling the web is not a programming task, but an algorithm design and system design challenge because of the web content is very large. At present, only Google claims to have indexed over 3 billion web pages. The web has doubled every 9-12 months and the changing rate is very high [1, 2, 3]. About 40% web pages change weekly  when we consider lightly change, but when we consider changing by one third or more than the changing rate is about 7% weekly .
Researchers are developing new scheduling policy for downloading pages for the world wide web which guarantees that, even if we want do not download all the web pages we still download the most important (by the user point of view) ones. As the size of Internet data grows, it will be very vital to download the important ones first, as it will be impossible to download all of them.
The rest of the paper is organized as follows. Section2 is explained about the fundamentals of web crawling. Section3 gives detail about web crawler strategies with diagrams. Section4 has a critical analysis with tables. The research scope is in section 5. Conclusion and references are at last.
The paper surveys several crawling methods or algorithms that are used for downloading the web pages from the World Wide Web. We believe that all of the algorithms discuss in this paper are well effective and high performance for web search, reduce the network traffic and crawling costs, but overall advantages and disadvantage favor more for By using HTTP Get Request and also Dynamic Web Page and download updated web pages By the using of the filter is produce relevant results.
The Kavian Scientific Research Association (KSRA) is a non-profit research organization to provide research / educational services in December 2013. The members of the community had formed a virtual group on the Viber social network. The core of the Kavian Scientific Association was formed with these members as founders. These individuals, led by Professor Siavosh Kaviani, decided to launch a scientific / research association with an emphasis on education.
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FULL Paper PDF file:SURVEY OF WEB CRAWLING ALGORITHMS
SURVEY OF WEB CRAWLING ALGORITHMS
Advances in Vision Computing: An International Journal
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Professor Siavosh Kaviani was born in 1961 in Tehran. He had a professorship. He holds a Ph.D. in Software Engineering from the QL University of Software Development Methodology and an honorary Ph.D. from the University of Chelsea.