Web Crawler

Have you heard about web crawlers? How is a web crawler helpful in a web site? Let us see what a web crawler is. It is an internet bot that browses the World Wide Web systematically for the purpose of web indexing. It is called by different names, such as a web spider, an ant, an automatic indexer, or a web scutter.

Web Crawling

To index a webpage or to update the web content, web search engines and some other sites use web crawling or spidering software. Also these web crawlers copy all the pages that they visit for later processing by a search engine and indexes the downloaded pages so that the users can access these pages much more quickly.These web crawlers can also validate hyperlinks and HTML codes and can also be used for web scraping.

Let us see how a web crawler indexes a page. A web crawler selects a list of URLs to visit, called seeds. When the crawler visits these URL, it detects all the hyperlinks and adds them to the list of URLs to visit, called the crawl frontier. URLs from the crawl frontier are repeatedly visited according to a set of policies.

Mirroring

Web crawlers provide user satisfaction and makes browsing easier. It reduces the network traffic in document space, resulting from search-directed access monitoring. And informing the users to modify the relevant areas of the webpage. Web crawlers can perform archiving and mirroring and this helps in populating the caches. Mirroring is the process of keeping a complete or partial copy of a website while archiving is the process of keeping the mirror of a large set of pages. Multifunctional robots can perform a number of the above tasks, sometimes simultaneously.

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