B we would check that on each leginstance of the

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(b) We would check that NUMBER_OF_AVAILABLE_SEATS on each LEG_INSTANCE of the flight is greater than 1 before doing any reservation (unless overbooking is permitted), and that the SEAT_NUMBER being reserved in SEAT_RESERVATION is available. (c) The INSERT operation into SEAT_RESERVATION will check all the key, entity integrity, and referential integrity constraints for the relation. The check that NUMBER_OF_AVAILABLE_SEATS on each LEG_INSTANCE of the flight is greater than 1 does not fall into any of the above types of constraints (it is a general semantic integrity constraint). (d) We will write a referential integrity constraint as R.A --> S (or R.(X) --> T) whenever attribute A (or the set of attributes X) of relation R form a foreign key that references the primary key of relation S (or T). FLIGHT_LEG.FLIGHT_NUMBER --> FLIGHT FLIGHT_LEG.DEPARTURE_AIRPORT_CODE --> AIRPORT FLIGHT_LEG.ARRIVAL_AIRPORT_CODE --> AIRPORT LEG_INSTANCE.(FLIGHT_NUMBER,LEG_NUMBER) --> FLIGHT_LEG LEG_INSTANCE.DEPARTURE_AIRPORT_CODE --> AIRPORT LEG_INSTANCE.ARRIVAL_AIRPORT_CODE --> AIRPORT LEG_INSTANCE.AIRPLANE_ID --> AIRPLANE FARES.FLIGHT_NUMBER --> FLIGHT CAN_LAND.AIRPLANE_TYPE_NAME --> AIRPLANE_TYPE CAN_LAND.AIRPORT_CODE --> AIRPORT AIRPLANE.AIRPLANE_TYPE --> AIRPLANE_TYPE SEAT_RESERVATION.(FLIGHT_NUMBER,LEG_NUMBER,DATE) --> LEG_INSTANCE 5.12 Consider the relation CLASS(Course#, Univ_Section#, InstructorName, Semester, BuildingCode, Room#, TimePeriod, Weekdays, CreditHours). This represents classes taught in a university with unique Univ_Section#. Give what you think should be various candidate keys and write in your own words under what constraints each candidate key would be valid. Answer: Possible candidate keys include the following (Note: We assume that the values of the Semester attribute include the year; for example "Spring/94" or "Fall/93" could be values for Semester): 1. {Semester, BuildingCode, Room#, TimePeriod, Weekdays} if the same room cannot be used at the same time by more than one course during a particular semester. 2. {Univ_Section#} if it is unique across all semesters.
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3. {InstructorName, Semester} if an instructor can teach at most one course during each semester. 4. If Univ_Section# is not unique, which is the case in many universities, we have to examine the rules that the university uses for section numbering. For example, if the sections of a particular course during a particular semester are numbered 1, 2, 3, ..., then a candidate key would be {Course#, Univ_Section#, Semester}. If, on the other hand, all sections (of any course) have unique numbers during a particular semester only, then the candidate key would be {Univ_Section#, Semester}. 5.13 Consider the following six relations for an order-processing database application in a company: CUSTOMER (Cust# , Cname, City) ORDER (Order# , Odate, Cust#, Ord_Amt) ORDER_ITEM (Order# , Item# , Qty) ITEM (Item# , Unit_price) SHIPMENT (Order# , Warehouse# , Ship_date) WAREHOUSE (Warehouse# , City) Here, Ord_Amt refers to total dollar amount of an order; Odate is the date the order was placed; Ship_date is the date an order is shipped from the warehouse. Assume that an order can be shipped from several warehouses. Specify foreign keys for this schema,
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