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BASI DI DATI 2 – PROFF . A. BRAGA , S. CERI SEPTEMBER 20 2011 – 2 h 30 m A. CONCURRENCY CONTROL (6 points) Given the following schedule: r 1(x) r2(y) r3(x) w1(x) r1(y) r2(x) w2(x) r3(z) w1(z) w2(y). Classify it with respect to the VSR, CSR, 2PL, TS mono, and TS multi classes. Motivate all the answers. B. XML and OODB (10 points) The following DTD describes travels organized by an agency. Suppose that all the non-specified elements are of type #PCDATA. <!ELEMENT Agency (Customer*,Travel*)> <!ELEMENT Customer (ID, Name, Lastname, Address, City) > <!ELEMENT Travel (Date, Participant*, Destination+) > <!ELEMENT Participant (CustomerID, AmountPaid) > <!ELEMENT Destination (City, State) > 1. Retrieve in XQuery all the customers who have never participated to a travel in China (3 pionts). 2. Retrieve in XQuery the destination where the agency has brought more visitors (if a customer has been in the same destination more than once, count her destination only once) (4 points). 3. Design an appropriate O-O schema to represent the same information and express Query 1 in OQL. (3 points) C. ACTIVE DATABASES (7 points) Consider a transport network of trains and buses: T RAIN PATH (FromPlace,ToPlace,DepartureTime ,ArrivalTime) BUS PATH (FromPlace,ToPlace,DepartureTime ,ArrivalTime) MOUNTAIN RESORT (Place ) Build a trigger system that lists the mountain resorts that can be reached from Milan with a train ride folllowed by a bus trip, assuming only a change from train to bu s within 3 hours and in the same day. Assume times in HH MM format and assume the availability of appropr iate functions to calculate distances in minutes. Assume that the table BusPath is initially empty an d that it can be modified with insertions, deletion s and updates. Build and maintain the list of mountain…