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Web Crawler

    Web Crawler Editor's Picks

    • Advanced Search Techniques

      There are billions of websites on the Internet. That's just the ones that the major search engines have already indexed. New pages crop up on the web daily and the content on existing pages can change. Learning advanced search techniques not only saves you time, it also helps you find the most relevant results. more »

    • How to Add a URL to Yahoo

      Yahoo! is a popular Internet search engine. With several billion websites in its search index, it is a good place to include your own web pages. Adding your URL to Yahoo! allows people who use the Yahoo! search engine to find your pages easily. Follow these steps to add your URL to Yahoo! more »

    • How Does McAfee Antivirus Software Work?

      McAfee Antivirus software works to block viruses from entering your computer system and kill or quarantine viruses that have some broken through the firewall.

      To begin protecting your computer system, McAfee Antivirus software updates its virus database by using an automatic web crawler that scans the Internet and identifies... more »

    Wikipedia

    Web crawler

    A Web crawler is a computer program that browses the World Wide Web in a methodical, automated manner. Other terms for Web crawlers are ants, automatic indexers, bots, and worms or Web spider, Web robot, or—especially in the FOAF community—Web scutterSee .

    This process is called Web crawling or spidering. Many sites, in particular search engines, use spidering as a means of providing up-to-date data. Web crawlers are mainly used to create a copy of all the visited pages for later processing by a search engine that will index the downloaded pages to provide fast searches. Crawlers can also be used for automating maintenance tasks on a Web site, such as checking links or validating HTML code. Also, crawlers can be used to gather specific types of information from Web pages, such as harvesting e-mail addresses (usually for spam).

    A Web crawler is one type of bot, or software agent. In general, 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 URLs to visit, called the crawl frontier. URLs from the frontier are recursively visited according to a set of policies.

    Crawling policies
    There are important characteristics of the Web that make crawling it very difficult:
    * its large volume,
    * its fast rate of change, and
    * dynamic page generation.

    These characteristics combine to produce a wide variety of possible crawlable URLs.

    The large volume implies that the crawler can only download a fraction of the Web pages within a given time, so it needs to prioritize its downloads. The high rate of change implies that by the time the crawler is downloading the last pages from a site, it is very likely that new pages have been added to the site, or that pages have already been updated or even deleted.

    The number of pages being generated by server-side software has also made it difficult for web crawlers to avoid r read more at » http://en.wikipedia.org/wiki/Web+crawler

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