Database Processing, Ninth Edition
CHAPTER 4
The Relational Model and Normalization
True-False Questions
1.
A relation is a three-dimensional table.
Answer: False
Page: 120
Level: moderate
2.
A characteristic of a relation is that the cells of the relation hold a single value.
Answer: True
Level: easy
Page: 120
3.
A characteristic of a relation is that the rows of a relation may hold identical values.
Answer: False
Level: moderate
Page: 120
4.
The columns of a relation are sometimes called “tuples.”
Answer: False
Level: easy
Page: 122
5.
Keys are always unique.
Answer: False
Page: 122
Level: easy
6.
A tuple is a group of one or more columns that uniquely identifies a row.
Answer: False
Level: easy
Page: 122
7.
A row can be uniquely identified by a key.
Answer: True
Page: 122
Level: easy
8.
A key can be composed of a group of attributes taken together.
Answer: True
Level: easy
Page: 122
9.
It is possible to have a relation that does not have a key.
Answer: False
Level: hard
Page: 123
10.
Attribute Y is functionally dependent on attribute X if the value of attribute X determines
the value of Y.
Answer: True
Level: moderate
Page: 123
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Chapter 4 - The Relational Model and Normalization
11.
The functional dependency noted as A  B, means that the value of A can be determined
from the value of B.
Answer: False
Level: easy
Page: 123
12.
In the functional dependency shown as A  B, B is the determinant.
Answer: False
Level: moderate
Page: 123
13.
Functional dependencies can involve groups of attributes.
Answer: True
Level: easy
Page: 124
14.
A determinant of a functional dependency may or may not be unique in a relation.
Answer: True
Level: moderate
Page: 125
15.
A primary key functionally determines an entire row.
Answer: True
Page: 123
Level: hard
16.
If a table meets the minimum definition of a relation, it has an effective or appropriate structure.
Answer: False
Level: moderate
Page: 125
17.
Undesirable consequences of changing the data in a relation are called “modification anomalies.”
Answer: True
Level: moderate
Page: 125
18.
A deletion anomaly exists when deleting data about one entity results in the loss of data about
another entity.
Answer: True
Level: easy
Page: 125
19.
A constraint, based on a business rule, that requires an instance of an entity to exist in one relation
before it can be referenced in another relation is called an insertion anomaly.
Answer: False
Level: hard
Page: 126-127
20.
A referential integrity constraint is based on a business rule.
Answer: True
Level: moderate
Page: 127
21.
The essence of normalization is taking a relation that has more than one theme
and breaking it into multiple relations that each have only one theme.
Answer: True
Level: easy
Page: 127
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Chapter 4 - The Relational Model and Normalization
22.
Breaking a relation into two or more relations may create the need for a referential
integrity constraint to be defined.
Answer: True
Level: moderate
Page: 127
23.
Relations are classified into “normal forms” based on the types of modification anomalies
that they are vulnerable to.
Answer: True
Level: hard
Page: 127
24.
The only normal form that guarantees that a relation is free from every possible type of
anomaly is 5NF.
Answer: False
Level: hard
Page: 127-128
25.
Any table that meets the definition of a relation is in 2NF.
Answer: False
Level: easy
Page: 128
26.
A relation is in first normal form if all of its non-key attributes are dependent on part of the key.
Answer: False
Level: moderate
Page: 128
27.
To be in second normal form, a relation must contain no partial dependencies.
Answer: True
Level: moderate
Page: 128
28.
A relation is in second normal form if it is in first normal form and all of its non-key
attributes are dependent on the entire key.
Answer: True
Level: moderate
Page: 128
29.
Relations that have a composite key and are in 1NF are automatically in 2NF.
Answer: False
Level: easy
Page: 128
30.
A transitive dependency exists when a non-key attribute is determined by only part of the key.
Answer: False
Level: moderate
Page: 129
31.
A relation is in 3NF if it is in 2NF and contains no transitive dependencies.
Answer: True
Level: easy
Page: 129
32.
A relation can have only one candidate key.
Answer: False
Page: 130
4-3
Level: moderate
Chapter 4 - The Relational Model and Normalization
33.
A relation is in Boyce-Codd Normal Form if it is in 3NF and every determinant
is a candidate key.
Answer: True
Level: easy
Page: 131
34.
A multi-value dependency exists when a relation has at least three attributes, two of which
are multi-value and their values depend only on the third attribute.
Answer: True
Level: hard
Page: 132
35.
A relation is in 4NF if it is in 3NF and contains no multi-value dependencies.
Answer: True
Level: moderate
Page: 132
36.
Fifth normal form deals with obscure problems with transitive dependencies.
Answer: False
Level: easy
Page: 133
37.
A relation is in DK/NF if every domain is the logical consequence of the definition of constraints
and keys.
Answer: False
Level: hard
Page: 133
38.
In considering DK/NF, a constraint includes any rule governing static values in the relation
except constraints that are time-based.
Answer: True
Level: moderate
Page: 133
39.
There is no known algorithm for converting a relation into DK/NF.
Answer: True
Level: moderate
Page: 134
40.
If A  B and B  A, then A and B have a many-to-many attribute relationship.
Answer: False
Level: moderate
Page: 138
41.
Attributes that have a one-to-one attribute relationship must occur together in at least one relation.
Answer: True
Level: moderate
Page: 138
42.
It is generally undesirable to have attributes that have a one-to-one attribute relationship appear in
more than one relation together.
Answer: True
Level: hard
Page: 139
43.
In general, a row of a relation should have all of the data about one instance of the relation’s
theme.
Answer: True
Level: moderate
Page: 141
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Chapter 4 - The Relational Model and Normalization
44.
De-normalization is the process of constructing relations by synthesis of attribute relationships.
Answer: False
Level: moderate
Page: 141
45.
Relations may be unnormalized or de-normalized to improve database performance.
Answer: True
Level: easy
Page: 143-144
Multiple Choice Questions
46.
A relation is also known as
a.)
a table
b.)
a tuple
c.)
a relationship
d.)
an attribute
e.)
a field
.
Level: easy
Page: 122
47.
A tuple is also known as a
a.)
table
b.)
relation
c.)
row
d.)
field
e.)
file
.
Level: moderate
Page: 122
48.
An attribute is also known as a
a.)
table
b.)
relation
c.)
row
d.)
field
e.)
file
.
Level: moderate
Page: 122
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Chapter 4 - The Relational Model and Normalization
49.
Which of the following, if any, is not true about keys?
a.)
can be a single attribute
b.)
can be a group of attributes taken together
c.)
can uniquely identify a row
d.)
must be functionally determined by another attribute
e.)
All of the above are true.
Level: moderate
Page: 123-125
50.
A functional dependency in a relation
a.)
usually involves a formula
b.)
always involves a primary key
c.)
exists among tuples
d.)
must always be removed through normalization
e.)
none of the above
.
Level: moderate
Page: 123
51.
Which of the following is known to be true from the functional dependency shown as (A, B) 
(C, D)?
a.)
A is the determinant of C
b.)
A and B together are determined by C and D together
c.)
A and B together determine D
d.)
C and D together determine A
e.)
A determines B
Level: moderate
Page: 125
52.
Which of the following is known to be true from the functional dependency
shown as A  (X, Y)?
a.)
X is functionally dependent on A
b.)
A determines Y
c.)
A is a determinant
d.)
X and Y are functionally dependent on A
e.)
All of the above.
Level: moderate
Page: 123-125
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Chapter 4 - The Relational Model and Normalization
53.
If the removal of facts about one entity results in the unintentional lose of data about another
entity, this is referred to an a(n) ____________.
a.)
normalization anomaly
b.)
insertion anomaly
c.)
entity anomaly
d.)
deletion anomaly
e.)
removal anomaly
Level: moderate
Page: 125
54.
The notation CUST-CAR[License]  CAR-RENT[License] indicates
.
a.)
License in CAR-RENT is a subset of License in CUST-CAR.
b.)
Before a value can be entered in the License field of the CAR-RENT relation, it must
have a matching value in the License field of the CUST-CAR relation.
c.)
License in CUST-CAR is functionally dependent on License in CAR-RENT.
d.)
Before a value can be entered in the License field of the CUST-CAR relation, it must
have a matching value in the License field of the CAR-RENT relation.
e.)
CUST-CAR and CAR-RENT are functionally dependent on the License field.
Level: hard
Page: 126
55.
Which of the following is not true about normalization?
a.)
produces relations with a single theme
b.)
may create referential integrity constraints
c.)
reduces the number of functional dependencies in the schema
d.)
reduces anomalies
e.)
splits a poorly structured relation into two or more well-structured relations
Level: moderate
Page: 127
56.
A table that meets the definition of a relation is in
a.)
First Normal Form
b.)
Second Normal Form
c.)
Third Normal Form
d.)
Boyce-Codd Normal Form
e.)
Fourth Normal Form
Level: easy
Page: 128
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Chapter 4 - The Relational Model and Normalization
57.
Which of the following is not a requirement for 1NF?
a.)
cells must contain single values
b.)
all entries in a column must be of the same kind
c.)
no two rows may be identical
d.)
rows must be ordered by the value of the primary key
e.)
the order of the columns is insignificant
Level: moderate
Page: 120
58.
A relation is in 2NF if it is in 1NF and all its non-key attributes are
a.)
dependent on part of the primary key
b.)
dependent on all of the primary key
c.)
independent of the primary key
d.)
independent of each other
e.)
independent of any other relation
.
Level: moderate
Page: 128
59.
Which of the following is a requirement of 2NF?
a.)
must contain a partial dependency
b.)
must contain a composite primary key
c.)
must contain no partial dependencies
d.)
must contain no transitive dependencies
e.)
must contain a multi-valued dependency
Level: moderate
Page: 128
60.
A relation is in third normal form if it is in second normal form and
a.)
is dependent on part of the key
b.)
is dependent on all of the key
c.)
is independent of the key
d.)
has no transitive dependencies
e.)
is independent of any other relation
Level: moderate
Page: 129
61.
Which of the following is a requirement of 3NF?
a.)
must contain a partial dependency
b.)
must contain a composite key
c.)
must contain no partial dependencies
d.)
must contain no transitive dependencies
e.)
must contain a multi-valued dependency
Level: moderate
Page: 129
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Chapter 4 - The Relational Model and Normalization
EMPLOYEE (SSN, SupervisorID, Department)
Key: SSN
Functional Dependencies: SSN  SupervisorID
SupervisorID  Department
SSN
123-45-6789
234-56-7890
345-67-8901
456-78-9012
567-89-0123
678-90-1234
62.
SupervisorID
100
200
100
300
100
200
Department
Engineering
Marketing
Engineering
Production
Engineering
Marketing
Which type of dependency is present in the EMPLOYEE relation above?
a.)
partial dependency
b.)
transitive dependency
c.)
determinant dependency
d.)
multi-valued dependency
e.)
deletion dependency
Level: hard
Page: 129
63.
A relation is in Boyce-Codd normal form if it is in 3NF and
a.)
every determinant is a candidate key
b.)
every determinant is a primary key
c.)
every attribute is a candidate key
d.)
there is more than one candidate key
e.)
there is more than one primary key
Level: moderate
Page: 131
64.
A “candidate key” is
.
a.)
a primary key.
b.)
any group of attributes that are a determinant
c.)
functionally dependent on the non-key attributes
d.)
an attribute or group of attributes that can be the primary key
e.)
the primary key selected to be the key of a relation
Level: easy
Page: 123
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Chapter 4 - The Relational Model and Normalization
65.
A multi-value dependency exists when a relation has
.
a.)
at least two attributes, both of them are multi-value, and their values depend on each
other
b.)
at least two attributes, one of them is multi-value, and its value depends on the other
c.)
at least three attributes, two of them are multi-value, and their values depend on
only the third attribute
d.)
at least three attributes, one of them is multi-value, and its value depends on the other two
attributes
e.)
at least three attributes, all of them are multi-value, and their values depend on each other
Level: hard
Page: 132
66.
A relation is in fourth normal form if it is in BCNF and it has no
a.)
transitive dependencies
b.)
multi-value dependencies
c.)
partial dependencies
d.)
deletion dependencies
e.)
referential integrity conflicts
.
Level: easy
Page: 132
67.
The anomalies addressed by moving from BCNF to 4NF generally deal with
a.)
excessive updates and redundancy of data for each entity
b.)
inability to uniquely identify an entity
c.)
inability to reconstruct relations once they have been decomposed
d.)
creation of identical rows in a relation
e.)
functional dependencies
Level: hard
Page: 132
68.
Fifth normal form deals with
.
a.)
excessive updates and redundancy of data for each entity
b.)
inability to uniquely identify an entity
c.)
inability to reconstruct relations once they have been decomposed
d.)
creation of identical rows in a relation
e.)
dependencies between referential integrity constraints
Level: moderate
Page: 133
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Chapter 4 - The Relational Model and Normalization
69.
The advantage of having a relation in domain/key normal form is that
a.)
it takes less storage space than other normal forms
b.)
it is easily obtained from Boyce-Codd normal form
c.)
there is a relatively simple algorithm for obtaining DK/NF
d.)
it is obtained by enforcing referential integrity constraints
e.)
it is guaranteed to have no modification anomalies
.
Level: easy
Page: 133
70.
A relation is in domain/key normal form if
.
a.)
every key of the relation is a logical consequence of the definition of constraints and
determinants
b.)
every key of the relation is a logical consequence of the definition of constraints and
domains
c.)
every constraint on the relation is a logical consequence of the definition of keys and
determinants
d.)
every constraint on the relation is a logical consequence of the definition of keys and
domains
e.)
every domain of the relation is a logical consequence of the definition of keys and
constraints
Level: moderate
Page: 133
71.
In the definition of DK/NF, which of the following is a type of constraint that is excluded from
consideration?
a.)
edit rules
b.)
intra-relation constraints
c.)
functional dependencies
d.)
time-based constraints
e.)
inter-relation constraints
Level: moderate
Page: 133
72.
Synthesizing relations means that the developers start with a
a.)
relation containing functional dependencies
b.)
relation without any functional dependencies
c.)
set of attributes with certain functional dependencies
d.)
set of domains and their constraints
e.)
set of anomalies based on dependencies
Level: moderate
Page: 138
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Chapter 4 - The Relational Model and Normalization
73.
If two attributes A and B have a one-to-one attribute relationship, it is shown as
a.)
b.)
c.)
d.)
e.)
.
A  B and B  A
A  B, but B not  A
B  A, but A not  B
A not  B and B not  A
AB
Level: moderate
Page: 138
74.
If two attributes A and B have a many-to-one attribute relationship, it is shown as
a.)
A  B and B  A
b.)
A  B, but B not  A
c.)
B  A, and A  B
d.)
A not  B and B not  A
e.)
AB
.
Level: moderate
Page: 138
75.
If two attributes A and B have a many-to-many attribute relationship, it is shown as
a.)
A  B and B  A
b.)
A  B, but B not  A
c.)
B  A, and A  B
d.)
A not  B and B not  A
e.)
AB
Level: moderate
Page: 138
76.
If two attributes A and B have a one-to-one attribute relationship in the relation R1(A,B,C),
then the primary key is
.
a.)
A
b.)
B
c.)
A or B
d.)
A and B
e.)
C
Level: easy
Page: 139
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Chapter 4 - The Relational Model and Normalization
77.
If two attributes A and B have a many-to-one attribute relationship in the relation R2(A,B,C),
then the primary key is
.
a.)
A
b.)
B
c.)
A or B
d.)
A and B
e.)
C
Level: easy
Page: 139
78.
When creating a database with attributes that have a one-to-one attribute relationship ________ .
a.)
the two attributes must appear in a relation together
b.)
the two attributes usually only appear in one relation together
c.)
other attributes that are functionally dependent on either of them may appear in a relation
with them
d.)
either of the attributes can appear in relations without the other
e.)
all of the above
Level: moderate
Page: 139-140
79.
If two attributes A and B have a many-to-many attribute relationship in the relation R3(A,B,C),
then the primary key is
.
a.)
A
b.)
B
c.)
A or B
d.)
A and B
e.)
C
Level: easy
Page: 139
80.
If two attributes G and H have a many-to-one relationship exist in a relation R4(G, H, J) where
J is a third attribute appearing in the relation, then
.
a.)
G  H and G  J
b.)
G  H, but H  J
c.)
(G, H)  J
d.)
J  (G, H)
e.)
J  G, and J  H
Level: moderate
Page: 139
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Chapter 4 - The Relational Model and Normalization
81.
If two attributes A and B have a many-to-many attribute relationship, it is shown as
a.)
A  B and B  A
b.)
A  B, but B not  A
c.)
B  A, and A  B
d.)
A not  B and B not  A
e.)
AB
Level: moderate
Page: 139
82.
When a relation has a key consisting of multiple attributes, you can add a new attribute to the
relation ______________.
a.)
without any restriction
b.)
so long as it is functionally dependent on part of the key
c.)
so long as it is functionally dependent on all of the key
d.)
so long as it is functionally dependent on a non-key attribute
e.)
so long as it is a candidate key
Level: moderate
Page: 140
83.
If two attributes A and B that have a many-to-many attribute relationship, and a third attribute C
also appears in the relation expressing the many-to-many relationship, then ______________.
a.)
A  B and B  C
b.)
B  A, but A  C
c.)
(A, B)  C
d.)
C  (A, B)
e.)
C A, and C  B
Level: moderate
Page: 139
84.
In general, a row in a relation should have all of the data about ___________.
a.)
one instance of the relation's theme
b.)
each instance of the relation's theme
c.)
every instance of the relation's theme
d.)
no instance of the relation's theme
e.)
the relation's functional dependencies
Level: easy
Page: 141
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Chapter 4 - The Relational Model and Normalization
85.
Database performance can be improved through appropriate use of ____________.
a.)
uncontrolled redundancy
b.)
de-normalization
c.)
data integrity violations
d.)
synchronous dependencies
e.)
both a and b
Level: easy
Page: 143-144
Fill in the Blank Questions
86.
A(n) relation is a two-dimensional table.
Level: easy
Page: 120
87.
In relational terms, a row is called a(n)
Level: easy
Page: 122
tuple .
88.
In relational terms, a column is called a(n)
Level: easy
Page: 122
89.
A(n) composite key
Level: easy
Page: 122
attribute .
is a group of attributes that uniquely identifies a row.
90.
A(n) candidate key is one of a group of keys that may serve as the primary key.
Level: easy
Page: 123
91.
A(n)
Level: easy
Page: 123
primary key is a group of one or more attributes that uniquely identifies a row.
92.
A key functionally determines the entire
Level: easy
Page: 123
row .
93.
A(n) functional dependency is a relationship between attributes such that if we know the value
of one attribute, we can determine the value of the other attribute.
Level: easy
Page: 123
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Chapter 4 - The Relational Model and Normalization
94.
If by knowing the value of A, we can find the value of B, then we would say that
B is functionally dependent on A.
Level: moderate
Page: 123
95.
In functional dependencies, the attribute whose value is known or given is
referred to as the determinant .
Level: moderate
Page: 123
96.
Unlike determinants, primary keys are always unique.
Level: easy
Page: 125
97.
For some relations, changing the data can have undesirable consequences
called modification anomalies .
Level: moderate
Page: 125
98.
Every time we break up a relation during the normalization process, we may
create referential integrity constraints.
Level: moderate
Page: 127
99.
Normal forms are nested so that if a relation is in 2NF, it is also in 1NF.
Level: easy
Page: 127
100.
A relation that is in domain / key normal form is assured to be free from all anomalies.
Level: moderate
Page: 128
101.
Any table that meets the definition of a(n)
Level: easy
Page: 128
102.
If a table is a relation then it is in
Level: easy
Page: 128
relation is said to be in first normal form.
1NF .
103.
To be in 1NF, the cells of a table must contain a(n)
Level: hard
Page: 120
104.
single
value.
A relation is in 2NF if it is in 1NF and all of its non-key attributes are
dependent on all of the key .
Level: moderate
Page: 128
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Chapter 4 - The Relational Model and Normalization
105.
A relation is in second normal form if all its non-key attributes are dependent on the entire
key.
Level: easy
Page: 128
106.
A relation is in 2NF if it is in 1NF and has no partial dependencies .
Level: easy
Page: 128
107.
A relation is in third normal form if it is in second normal form
and has no transitive dependencies .
Level: moderate
Page: 129
108.
A defining requirement for
candidate key.
Level: moderate
Page: 131
Boyce-Codd normal form is that every determinant must be a
109.
A relation is in BCNF if it is in 3NF and every
Level: moderate
Page: 131
determinant is a candidate key.
110.
A relation is in BCNF if it is in 3NF and every determinant is a(n)
Level: moderate
Page: 131
candidate key .
111.
Relations in BCNF have no anomalies in regard to functional dependencies .
Level: hard
Page: 131
112.
A(n) multi-value dependency exists when a relation has at least three attributes, two of them
are multi-value, and their values depend on only the third attribute.
Level: easy
Page: 132
113.
A relation is in 4NF if it is in BCNF and it has no
Level: moderate
Page: 132
multi-value dependencies .
114.
Fifth normal form deals with obscure dependencies that may not have any practical
consequences.
Level: moderate
Page: 133
115.
Domain / key normal form requires that every
definition of domains and keys.
Level: moderate
Page: 133
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constraint be a logical consequence of the
Chapter 4 - The Relational Model and Normalization
116.
In regard to DK/NF, a constraint is broadly defined to include all types of constraints
except time-based constraints.
Level: hard
Page: 133
If the functional dependencies between two attributes is A  B and B  A, then they
have a(n) one-to-one attribute relationship.
Level: easy
Page: 138
117.
If the functional dependencies between two attributes is A  B, but B not  A, then they
have a(n) many-to-one attribute relationship.
Level: moderate
Page: 138
118.
If the functional dependencies between two attributes is A not  B and B not  A, then they
have a(n) many-to-many attribute relationship.
Level: moderate
Page: 138
119.
When synthesizing relations, if two attributes have the relationship A  B and B  A, then
create a relation with A or B as the key.
Level: easy
Page: 139
120.
When synthesizing relations, if two attributes have the relationship A  B, but not B  A, then
create a relation with A as the key.
Level: easy
Page: 139
121.
When synthesizing relations, if attributes have the dependencies (A, B)  C, then create
a relation with
(A, B) as the key.
Level: moderate
Page: 139
122.
123.
Relations are sometimes left unnormalized to improve
Level: easy
Page: 141
performance .
Essay Questions
124.
Describe the requirements that a table must meet to qualify as a relation.
In order for a table to meet the requirements of a relation, it must satisfy certain conditions.
First, the rows contain data about an entity or some portion of the entity. Second, the columns
contain data that represent attributes of the entity – each column must contain the same kind of
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Chapter 4 - The Relational Model and Normalization
data for all rows – and each column must have a unique name. Third, the cells must contain
single values – no group or array values are allowed. Finally, the rows must be unique. It is
worth noting that the order of the columns and the rows is insignificant.
125.
Explain the relationships among primary keys, functional dependencies, and uniqueness.
All primary keys represent a functional dependency, since each primary key functionally
determines the entire row. Since the primary key determines the entire row, if a primary key were
duplicated in a relation, then the entire row would have to be duplicated. Since a relation can
contain no duplicate rows, the primary key must be unique. However, all functional
dependencies are not represented through primary keys. Therefore, the determinant of a
functional dependency may or may not be unique.
126.
Explain the essence of normalization that is implemented through the use of normal forms.
The essence of normalization is to create relations that contain data on a single theme, and for
each row in a relation to contain all the data about that theme for a given entity. This essence is
implemented in the normal forms by taking a relation that contains data on more than one theme
and splitting it into multiple relations that each contain data on a single theme.
127.
Explain the concept of a transitive dependency and give an example not included in the book.
A transitive dependency is evidenced through a functional dependency among non-key attributes.
If the key of a relation determines the value of one attribute because it can determine the value of
another attribute, then a transitive dependency exists. For example, if an employee is assigned a
computer to work on and the computer has an assigned IP address for the corporate network, the
relation EMPLOYEE (EmployeeID, ComputerID, IPaddress) with EmployeeID as the key,
contains a transitive dependency. The IP address is not really determined by the EmployeeID,
but rather by the ComputerID, such that EmployeeID determines IPaddress only because
EmployeeID determines ComputerID which in turn determines IPaddress. The functional
dependencies can be shown asEmployeeID  ComputerID
ComputerID  IPaddress
Therefore EmployeeID  ComputerID  Ipaddress
128.
Explain the practical value that DK/NF has in the real world, and why that practical
value is limited.
Domain key normal form has practice value as a database design objective. Since a relation in
domain key normal form is guaranteed to contain no anomalies, it is the preferred normalization
goal. Many relations can achieve DK/NF while others cannot. The fact that many relations
cannot be placed in DK/NF, and there is no method for determining which can and which cannot,
limits the practical value of DK/NF as a design goal. Further, there is no algorithm for
achieving DK/NF even for relations that can reach this ultimate level of normalization.
129.
Contrast the analytic and synthetic perspectives of relational design.
The analytic perspective of relational design starts from a relation and attempts to identify the
anomalies to which it is vulnerable in order to determine which normal form it is in. The
synthetic perspective starts with a collection of attributes and their functional dependencies. It
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Chapter 4 - The Relational Model and Normalization
then attempts to determine which relations should be formed from these attributes based on their
attribute relationships.
130.
Explain what it means to de-normalize, and why it may be appropriate.
De-normalization is the process of taking a normalized set of relations and converting them into
a smaller set of relations that is in a lower normal form and thus vulnerable to a greater number
of anomalies. While the fully normalized set of relations is more desirable from a theoretical
perspective, it does have some disadvantages. The greater the number of relations in the
database, the more work that is required by the database whenever data must be retrieved from
multiple relations to reconstruct the users’ view of the data. In some circumstances, the
anomalies introduced by de-normalizing a data model may be considered an acceptable cost for
the performance improvement from reducing the overhead work performed by the database.
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