For example, a simple online photo gallery may offer three options to users, as specified through HTTP GET parameters in the URL. Endless combinations of HTTP GET (URL-based) parameters exist, of which only a small selection will actually return unique content. WEB CRAWLER NZB SEARCH SOFTWAREThe number of possible crawlable URLs being generated by server-side software has also made it difficult for web crawlers to avoid retrieving duplicate content. The high rate of change implies that the pages might have already been updated or even deleted. 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. URLs from the frontier are recursively visited according to a set of policies. 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. In general, it starts with a list of URLs to visit, called the seeds. Also, crawlers can be used to gather specific types of information from Web pages,such as harvesting e-mail addresses (usually for sending spam).Ī Web crawler is one type of bot, or software agent. Crawlers can also be used for automating maintenance tasks on a Web site, such as checking links or validating HTML code. 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. ![]() Many sites, in particular search engines, use spidering as a means of providing up-to-date data. ![]() This process is called Web crawling or spidering. Other terms for Web crawlers are ants, automatic indexers, bots, Web spiders, Web robots, or-especially in the FOAF community- Web scutters. A Web crawler is a computer program that browses the World Wide Web in a methodical, automated manner or in an orderly fashion.
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