•Mediated schema:
• Movie(title, dir, year, genre),
• Schedule(cinema, title, time).
•Source S4: S4(cinema, genre)
•Create View Movie AS
• select NULL, NULL, NULL, genre
•
from S4
• Create View Schedule AS
• select cinema, NULL, NULL
• from S4.
•But what if
we want to find which cinemas are playing comedies?
•