Search engines were invented to break down web sites’ barriers, letting users query the whole Web rather than multiple sites separately. However, as search engines cannot access to the struc- tured databases within web sites, they can only offer unstructured, text-based search. So while each site (., ) can offer sophisticated structured browsing and searching experi- ence, that experience ends at the boundary of the site, beyond which the structures of the data within that site is lost. In parallel, screenscrapers were invented to extract fragments within web pages (., weather forecasts, stockquotes, and news article summaries) and re-purpose them in personalized ways
