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Unformatted text preview: Relational Algebra and Calculus 37 Exercise 4.5 Consider the following relations containing airline ﬂight information: Flights( ﬂno: integer , from: string , to: string , distance: integer , departs: time , arrives: time ) Aircraft( aid: integer , aname: string , cruisingrange: integer ) Certified( eid: integer , aid: integer ) Employees( eid: integer , ename: string , salary: integer ) Note that the Employees relation describes pilots and other kinds of employees as well; every pilot is certified for some aircraft (otherwise, he or she would not qualify as a pilot), and only pilots are certified to ﬂy. Write the following queries in relational algebra, tuple relational calculus, and domain relational calculus. Note that some of these queries may not be expressible in relational algebra (and, therefore, also not expressible in tuple and domain relational calculus)! For such queries, informally explain why they cannot be expressed. (See the exercises at the end of Chapter 5 for additional queries over the airline schema.) 1. Find the eid s of pilots certified for some Boeing aircraft....
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- Fall '12
- Relational model, TRC, Domain relational calculus, Relational calculus, Tuple relational calculus