With the proliferation of dynamic Web sites, whose contents are provided by online databases in response to querying, deep-Web search aims at finding information from this “hidden” or “deep” Web. Current search engines crawl and index pages from statically linked Web pages, or the “surface” Web. As such crawlers cannot effectively query online databases, much of the deep Web is not generally covered by current search engines, and thus remains invisible to users. A deep-Web search system queries over online databases to help users search these databases uniformly.
In the last few years, the Web has been rapidly “deepened” by the massive networked databases on the Internet. While the surface Web has linked billions of static HTML pages, a far more significant amount of information is hidden in the deep Web, behind the query forms of searchable databases. A July 2000 survey  claims that there were 500 billion hidden pages in...
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