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Database Languages

eXercise 1


The Relational Model

A. Referring to the following tables that attempt to summarise sporting prowess at an international meet (only partial data is shown).

(a)
Nation Medals
Russia 11G, 8S, 3B
Czecoslovakia 9G 6S, 5B
France 5G, 4S, 2B
South Africa 2G, 5B
Australia 1G, 3S
(b)
Nation Gold Silver Bronze
Russia 11 8 3
Czecoslovakia 9 6 5
France 5 4 2
South Africa 2 0 5
Australia 1 3 0
(c)
Nation Medal Tally
Russia Gold 11
Russia Silver 8
Russia Bronze 3
Czecoslovakia Gold 9
Czecoslovakia Silver 6
: : :
  1. Which of the above conforms to the relational model of data? In cases where there are exceptions to the model, detail them.
  2. For those tables that conform to the relational model, detail the possible benefits of having the data stored in that form, along with possible problems. (hint: ask yourself what types of questions (queries) are difficult with one form that are simpler in another)

B. The following tables make different assumptions about the data, what is the difference?.

(a)
Team Wins
Broncos 4
Cockroaches 6
Tigers 0
(b)
Team Wins
Broncos 4
Cockroaches 6
Tigers

C. Given that the illustrated populations in the following tables are signifigant, identify the Primary Key for each relation.

(a)
Name Gender
Fred M
Phyllis F
Olivia M
(b)
Student Subject
Fred English
Craig English
Fred Geography
(c)
Language
SQL
Prolog
Pascal
COBOL
ASM
Modula 2
Visual Basic
(d)
Language Recursive
Pascal Yes
SQL No
Prolog Yes
COBOL No
(e)
Manufacturer Model Year
Ford Mondeo 1997
Ford Falcon 1995
Mitsubishi Magna 1997
Toyota Corolla 1997
Toyota Corolla 1988
(f)
Day Subject Period
Mon Physics 3
Tues Physics 3
Tues Physics 5
Tues Geography 5


D.
Given the population in the following tables, identify the Primary Key for the relation.

School Event Place
BSHS 13 2
BSHS 14 2
GT 13 1
  1. If ties are allowed?
  2. If ties are not allowed?

Solutions

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