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google crawler google crawler Presentation Transcript

  • K.RAJU 10601A0519 4th CSE
  •  A Web crawler is a computer program that browses the World Wide Web in a methodical,  automated manner or in an orderly fashion. What Google Crawler Are?  Crawlers are computer programs that roam the Web with the goal of automating specific related to the Web.  The role of Crawlers is to collect Web Content.
  •  A key motivation for designing Web crawlers has been to retrieve Web pages and add their  Representations to a local repository.  A Google crawler starts with a list of URLs to visit, called the seeds. As the crawler visits these URLs, it identifies all the hyperlinks in the page and adds them to the list of URLs to visit, called the crawl frontier. URLs from the frontier are recursively visited according to a set of policies.
  •  It starts with a list of URLs to visit, called the seeds As the crawler visits these URLs, it identifies all the hyperlinks in the page and adds them to the list of visited URLs, called the crawl frontier  URLs from the frontier are recursively visited according to a set of policies.
  •  The basic Algorithm: { Pick up the next URL Connect to the Server GET the URL When the pages arrives, get its Links (optionally do other stuff) REPEAT }
  •  Search Engine Marketing: SEM is all that a company can do to advertise itself on a search engine, including paid inclusion and other ads.  Search Engine Optimization: Process of improving the visibility of a website or a webpage in search engines via the "natural," or un-paid
  •  The name of the Google’s web crawler is Googlebot(Spider).  It’s a network of powerful computers that work together and visits web servers, requests thousands of pages at a time  1998 : Googlebot, S. Brin and L. Page.
  • • Yahoo! Slurp: Yahoo Search crawler. • Msnbot: Microsoft's Bing web crawler. • Googlebot : Google's web crawler. • WebCrawler : Used to build the first publicly-available full-text index of a subset of the Web. • World Wide Web Worm : Used to build a simple index of document titles and URLs. • Web Fountain: Distributed. modular crawler written in C++. • Slug: Semantic web crawler .
  •  Deepbot: Visits all the pages it can find on the web by harvesting every link it discovers and following it. It currently takes it about a month to perform this deep crawl.  Freshbot: Keeps the index fresh by visiting sites that change frequently at more regular intervals. The rate at which the website is updated dictates how often Freshbot visits it
  • Query Engine Index Interface Indexer Users Crawler Web A Typical Web Search Engine
  •  The process or program used by search engines to     download pages from the web for later processing by a search engine that will index the downloaded pages to provide fast searches. A program or automated script which browses the World Wide Web in a methodical, automated manner also known as web spiders and web robots. less used names- ants, bots and worms.
  •  Batch Crawlers- Crawl a snapshot of their crawl space, until reaching a certain size or time limit.  Incremental Crawlers- Continuously crawl their crawl space, revisiting URL to ensure freshness.  Focused Crawlers- Attempt to crawl pages pertaining to some topic/theme, while minimizing number of off topic pages that are collected.
  • Advantages •Cost-effective. •85% of users come from Search Engines rest 15% come from other ways. •Increased Brand Awareness. •Improved Visitor Experience. •Increase Revenue.
  • Disadvantages 1. Wastage of bandwidth. 2. Flash websites issue. How to overcome??? 1. Web sites and pages can specify that robots should not crawl/index certain areas. It means making a robot.txt file in the main directory of website. 2. Now yahoo is working on its crawler again so that it can pick flash websites.
  •  Web crawlers are an important aspect of the search engines.  Web crawling processes deemed high performance are the basic components of various Web services.  It is not a trivial matter to set up such systems: 1. Data manipulated by these crawlers cover a wide area. 2. It is crucial to preserve a good balance between random access memory and disk accesses.
  • Thank you!!
  • Questions…