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:
“The wind and the rain, gives this place a gleam that just isn’t natural. And the ground, alive with crawling things, crawling death.”
—Edward D. Wood, Jr. (1922–1978)
“Yet here at least an earnest sense
Of human right and weal is shown;
A hate of tyranny intense,
And hearty in its vehemence,
As if my brother’s pain and sorrow were my own.
O Freedom! if to me belong
Nor mighty Milton’s gift divine,
Nor Marvell’s wit and graceful song.
Still with a love as deep and strong
As theirs, I lay, like them, my best gifts on thy shrine!”
—John Greenleaf Whittier (1807–1892)
“Any newspaper, from the first line to the last, is nothing but a web of horrors.... I cannot understand how an innocent hand can touch a newspaper without convulsing in disgust.”
—Charles Baudelaire (1821–1867)