14.17 A company called FastCabs provides a taxi service to clients. The table shown in Figure 14.21 displays some details of client bookings for taxis. Assume that a taxi driver is assigned to a single taxi, but a taxi can be assigned to one or more drivers. (a) Identify the functional dependencies that exist between the columns of the table in Figure 14.21 and identify the primary key and any alternate key(s) (if present) for the table. (b) Describe why the table in Figure 14.21 is not in 3NF. (c) The table shown in Figure 14.21 is susceptible to update anomalies. Provide examples of how insertion, deletion, and modification anomalies could occur on this table. JobID JobDate Time driverID driverName taxiID clientID clientName jobPickUpAddress 1 25/07/14 10.00 D1 Joe Bull T1 C1 Anne Woo 1 Storrie Rd, Paisley 2 29/07/14 10.00 D1 Joe Bull ΤΙ CI 3 30/07/14 11.00 D2 Tom Win T2 C1 Anne Woo Anne Woo 1 Storrie Rd, Paisley 4 2/08/14 13.00 D3 Jim Jones T3 C2 Mark Tin 3 High Street, Paisley 1A Lady Lane, Paisley 5 2/08/14 13.00 D4 Steven Win T1 C3 John Seal 22 Red Road, Paisley 6 25/08/14 10.00 D2 Tom Win T2 C4 Karen Bow 17 High Street, Paisley Figure 14.21 Table displaying sample data for FastCabs. 429 43014.18 Applying normalisation to 3NF on the table shown in Figure 14.21 results in the formation of the three 3NF tables shown in Figure 14.22. (a) Identify the functional dependencies that exist between the columns of each table in Figure 14.22 and identify the primary key and any alternate and foreign key(s) (if present) for each table. (b) Describe why storing the FastCabs data across three 3NF tables avoids the update anomalies described in Exercise 14.17(b). (c) Describe how the original table shown in Figure 14.21 can be re-created through relational joins between primary key and foreign keys columns of the tables in Figure 14.22. JobID JobDateTime driverID 1 25/07/14 10.00 D1 2 29/07/14 10.00 D1 3 30/07/14 11.00 D2 2/08/14 13.00 D3 5 2/08/14 13.00 ᎠᏎ 6 25/08/14 10.00 D2 clientID C1 5 5 5 8 3 J C2 C3 C4 jobPickUpAddress 1 Storrier Rd, Paisley 1 Storrier Rd, Paisley 3 High Street, Paisley 1A Lady Lane, Paisley 22 Red Road, Paisley 17 High Street, Paisley drierID driverName taxiD D1 Joe Bull T1 D2 Tom Win T2 D3 Jim Jones T3 ᎠᏎ Steven Win T1clientID C1 C2 5 3 3 3 C3 C4 clientName Anne Woo Mark Tin John Seal Karen Bow
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