South China Agricultural University
Computing Science
2005-2006
Database Systems
Tutorial Set 4 (ANSWERS)
Tutorial Questions (Functional Dependency and Normalization)
1.
A relation NADDR is defined as follows.
NADDR = (name, street, city, state, postal_code)
where name is unique, and for any given postal code, there is just one city and
state
a. Give a set of FDs for this relation.
b. What are the candidate keys?
c. Is NADDR in3NF? 2NF? Explain why?
d. If NADDR is not in 3NF, normalize it into 3NF relations.
Ans:
a.
street
statue
name
city
postal_code
b.
The candidate key is Name
c.
It is in 2NF as there is dependency between nonkey attributes as postal-code
determines city and state
d.
NADDR = (name, street, city, state, postal_code) will be decomposed into
NADDR1 = (name, street, postal_code)
Postal = (postal_code, city, state)
2.
A database used in an order-entry system is to contain information about
customers, items and orders. The following information is to be included.
For each customer:
Customer number (unique)
“Ship-to” addresses (several per customer)
Balance
Credit limit
Discount
For each order:
Heading information: customer number, ship-to address, date of order
Detail lines (several per order): item number, quantity ordered
For each item:
Item number (unique)
Manufacturing plants
Quantity on hand at each plant
Stock danger level for each plant
Item description
For internal processing reasons a “quantity outstanding” value is associated with
each detail line of each order. This value is initially set equal to the quantity of
the item order and is (progressively) reduced to zero as (partial) shipments are
made.
The following semantic assumptions can be made:
• No two customers have the same ship-to address.
• Each order is identified by a unique order number.
• Each detail line within an order is identified by a line number, unique within
the order.
Draw a functional dependency diagram and design a set of the tables in the third
normal form (3NF) for the system.
Ans:
The functional dependency diagram.
BAL
ADDRESS
CUST #
CREDLIM
DISCOUNT
QTYORD
ORD #
DATE
QTYOUT
LINE #
DESCN
ITEM #
QTYOH
PLANT #
DANGER
The tables in third normal form (3NF)
CUST (CUST#, BAL, CREDLIM, DISCOUT)
PRIMARY KEY (CUST #)
SHIPTO (ADDRESS, CUST #)
PRIMARY KEY (ADDRESS)
ORDHEAD (ORD#, ADDRESS, DATE)
PRIMARY KEY (ORD#)
ORDLINE (ORD#, LINE#, ITEM#, QTYORD, QTYOUT)
PRIMARY KEY (ORD#, LINE#)
ITEM (ITEM#, DESCN)
PRIMARY KEY(ITEM#)
IP (ITEM#, PLANT#, QTYOH, DANGER)
PRIMARY KEY (ITEM#, PLANT#)