Crawling The Deep Web
A vast amount of web pages lie in the deep or invisible web. These pages are typically only accessible by submitting queries to a database, and regular crawlers are unable to find these pages if there are no links that point to them. Google's Sitemaps protocol and mod oai are intended to allow discovery of these deep-Web resources.
Deep web crawling also multiplies the number of web links to be crawled. Some crawlers only take some of the -shaped URLs. In some cases, such as the Googlebot, Web crawling is done on all text contained inside the hypertext content, tags, or text.
Strategic approaches may be taken to target deep-Web content. With a technique called screen scraping, specialized software may be customized to automatically and repeatedly query a given Web form with the intention of aggregating the resulting data. Such software can be used to span multiple Web forms across multiple Websites. Data extracted from the results of one Web form submission can be taken and applied as input to another Web form thus establishing continuity across the Deep Web in a way not possible with traditional web crawlers.
Pages built on AJAX are among those causing problems to web crawlers. Google has proposed a format of AJAX calls that their bot can recognize and index
Read more about this topic: Scutter
Famous quotes containing the words crawling, deep and/or web:
“But see, amid the mimic rout
A crawling shape intrude!”
—Edgar Allan Poe (1809–1849)
“We plunge
O dark river!
towards each other
into that element
a deep fall,
the eyes closing as if forever....”
—Denise Levertov (b. 1923)
“However, our fates at least are social. Our courses do not diverge; but as the web of destiny is woven it is fulled, and we are cast more and more into the centre. Men naturally, though feebly, seek this alliance, and their actions faintly foretell it.”
—Henry David Thoreau (1817–1862)