An expert system, using the explanation facility, can indicate all the facts and rules that were used in reaching a conclusion.
Answer the following statement true (T) or false (F)
True
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Showthat the schedule shown in Figure 21.13 for incorrect execution at SNAP- SHOT isolation can also occur when executing at OPTIMISTIC READ COMMITTED (Section 21.2.1) and will also be incorrect.
What will be an ideal response?
A user arrives at a railway station that she has never visited before, carrying a PDA that is capable of wireless networking. Suggest how the user could be provided with information about the local services and amenities at that station, without entering the station’s name or attributes. What technical challenges must be overcome?
What will be an ideal response?
Candidate keys that are not used for the primary key are ________ keys
Fill in the blank(s) with correct word
Formulate the following queries in relational algebra, tuple relational calculus, and domain relational calculus (the answers to these queries in SQL are given in the next section).
The following tables form part of a database held in a Relational Database Management System: Employee (empNo, eName, salary, position) Aircraft (aircraftNo, aName, aModel, flyingRange) Flight (flightNo, from, to, flightDistance, departTime, arriveTime) Certified (empNo, aircraftNo) where Employee contains details of all employees (pilots and non-pilots) and empNo is the key. AirCraft contains details of aircraft and aircraftNo is the key. Flight contains details of the flights and flightNo is the key. and Certified contains details of the staff who are certified to fly an aircraft, and empNo/aircraftNo form the key. (1) List all Boeing aircraft. (2) List all Boeing 737 aircraft. (3) List the employee numbers of pilots certified for Boeing aircraft. (4) List the names of pilots certified for Boeing aircraft. (5) List the aircraft that can fly nonstop from Glasgow to New York (flyingRange > flightDistance). (6) List the employee numbers of employees who have the highest salary. (7) List the employee numbers of employees who have the second highest salary. (8) List the employee numbers of employees who are certified for exactly three aircraft.