Interrelation dependencies
Consider the relation with schema Bookings(title,theater,city)
Under certain assumptions, it has the FD theater → city, but theater is
not a superkey. The BCNF decomposition yields relation schemas
Bookings1(theater,city) and Bookings2(theater,title).
These schemas and their FDs allow, e.g., the relation instances:
which violate the presumed FD title city → theater.
Thus, there are implicit dependencies between values in different relations.
We cannot check FDs separately in each relation to see such a dependency.
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