Querying the WWW

• Assume a virtual schema of the WWW, e.g.,

  • Course(number, university, title, prof, quarter)

• Every data source on the web contains the answer to a view over the virtual schema:

UW database: SELECT number, title, prof

FROM Course

WHERE univ=‘UW’ AND quarter=‘4/99’

Stanford database: SELECT number, title, prof, quarter

FROM Course

WHERE univ=‘Stanford’

User query: find all professors who teach “database systems”

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