Chapter 3: The Relational Data Model and Relational Database Constraints Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley. 1 CHAPTER 3: THE RELATIONAL DATA MODEL AND RELATIONAL DATABASE CONSTRAINTS Answers to Selected Exercises 3.11 - Suppose each of the following Update operations is applied directly to the database of Figure 3.6. Discuss all integrity constraints violated by each operation, if any, and the different ways of enforcing these constraints: (a) Insert < 'Robert', 'F', 'Scott', '943775543', '21-JUN-42', '2365 Newcastle Rd, Bellaire, TX', M, 58000, '888665555', 1 > into EMPLOYEE. (b) Insert < 'ProductA', 4, 'Bellaire', 2 > into PROJECT. (c) Insert < 'Production', 4, '943775543', '01-OCT-88' > into DEPARTMENT. (d) Insert < '677678989', null, '40.0' > into WORKS_ON. (e) Insert < '453453453', 'John', M, '12-DEC-60', 'SPOUSE' > into DEPENDENT. (f) Delete the WORKS_ON tuples with ESSN= '333445555'. (g) Delete the EMPLOYEE tuple with SSN= '987654321'. (h) Delete the PROJECT tuple with PNAME= 'ProductX'. (i) Modify the MGRSSN and MGRSTARTDATE of the DEPARTMENT tuple with DNUMBER=5 to '123456789' and '01-OCT-88', respectively. (j) Modify the SUPERSSN attribute of the EMPLOYEE tuple with SSN= '999887777' to '943775543'. (k) Modify the HOURS attribute of the WORKS_ON tuple with ESSN= '999887777' and PNO= 10 to '5.0'. Answers: (a) No constraint violations. (b) Violates referential integrity because DNUM=2 and there is no tuple in the DEPARTMENT relation with DNUMBER=2. We may enforce the constraint by: (i) rejecting the insertion of the new PROJECT tuple, (ii) changing the value of DNUM in the new PROJECT tuple to an existing DNUMBER value in the DEPARTMENT relation, or (iii) inserting a new DEPARTMENT tuple with DNUMBER=2. (c) Violates both the key constraint and referential integrity. Violates the key constraint because there already exists a DEPARTMENT tuple with DNUMBER=4. We may enforce this constraint by: (i) rejecting the insertion, or (ii) changing the value of DNUMBER in the new DEPARTMENT tuple to a value that does not violate the key constraint. Violates referential integrity because MGRSSN='943775543' and there is no tuple in the EMPLOYEE relation with SSN='943775543'. We may enforce the constraint by: (i) rejecting the insertion, (ii) changing the value of MGRSSN to an existing SSN value in EMPLOYEE, or (iii) inserting a new EMPLOYEE tuple with SSN='943775543'. (d) Violates both the entity integrity and referential integrity. Violates entity integrityChapter 3: The Relational Data Model and Relational Database Constraints Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley. 2 because PNO, which is part of the primary key of WORKS_ON, is null. We may enforce this constraint by: (i) rejecting the insertion, or (ii) changing the value of PNO in the new WORKS_ON tuple to a value of PNUMBER that exists in the PROJECT relation. Violates referential integrity because ESSN='677678989' and there is no tuple in the EMPLOYEE relation with SSN='677678989'. We may enforce the constraint by: (i) rejecting the insertion, (ii) changing the value of ESSN to an existing SSN value in EMPLOYEE, or (iii) inserting a new EMPLOYEE tuple with SSN='677678989'. (e) No constraint violations. (f) No constraint violations. (g) Violates referential integrity because several tuples exist in the WORKS_ON, DEPENDENT, DEPARTMENT, and EMPLOYEE relations that reference the tuple being deleted from EMPLOYEE. We may enforce the constraint by: (i) rejecting the deletion, or (ii) deleting all tuples in the WORKS_ON, DEPENDENT, DEPARTMENT, and EMPLOYEE relations whose values for ESSN, ESSN, MGRSSN, and SUPERSSN, respectively, is equal to'987654321'. (h) Violates referential integrity because two tuples exist in the WORKS_ON relations that reference the tuple being deleted from PROJECT. We may enforce the constraint by: (i) rejecting the deletion, or (ii) deleting the tuples in the WORKS_ON relation whose value for PNO=1 (the value for the primary key PNUMBER for the tuple being deleted from PROJECT). (i) No constraint violations. (j) Violates referential integrity because the new value of SUPERSSN='943775543' and there is no tuple in the EMPLOYEE relation with SSN='943775543'. We may enforce the constraint by: (i) rejecting the deletion, or (ii) inserting a new EMPLOYEE tuple with SSN='943775543'. (k) No constraint violations. 3.12 - Consider the AIRLINE relational database schema shown in Figure 3.8, which describes a database for airline flight information. Each FLIGHT is identified by a flight NUMBER, and consists of one or more FLIGHT_LEGs with LEG_NUMBERs 1, 2, 3, etc. Each leg has scheduled arrival and departure times and airports, and has many LEG_INSTANCEs--one for each DATE on which the flight travels. FARES are kept for each flight. For each leg instance, SEAT_RESERVATIONs are kept, as is the AIRPLANE used in the leg, and the actual arrival and departure times and airports. An AIRPLANE is identified by an AIRPLANE_ID, and is of a particular AIRPLANE_TYPE. CAN_LAND relates AIRPLANE_TYPEs to the AIRPORTs in which they can land. An AIRPORT is identified by an AIRPORT_CODE. Consider an update for the AIRLINE database to enter a reservation on a particular flight or flight leg on a given date. (a) Give the operations for this update. (b) What types of constraints would you expect to check? (c) Which of these constraints are key, entity integrity, and referential integrity constraints and which are not?Chapter 3: The Relational Data Model and Relational Database Constraints Copyright © 2011 Pearson Education, Inc. Publishing as Pearson Addison-Wesley. 3 (d) Specify all the referential integrity constraints on Figure 3.8. Answers: (a) One possible set of operations for the following update is the following: INSERT <FNO,LNO,DT,SEAT_NO,CUST_NAME,CUST_PHONE> into SEAT_RESERVATION; MODIFY the LEG_INSTANCE tuple with the condition: ( FLIGHT_NUMBER=FNO AND LEG_NUMBER=LNO AND DATE=DT) by setting NUMBER_OF_AVAILABLE_SEATS = NUMBER_OF_AVAILABLE_SEATS - 1; These operations should be repeated for each LEG of the flight on which a reservation is made. This assumes that the reservation has only one seat. More complex operations will be needed for a more realistic reservation that may reserve several seats at once. (b) We would check that NUMBER_OF_AVAILABLE_SEATS on each LEG_INSTANCE of the flight is greater than 1 before
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