Database Systems Design Implementation And Management 11th Edition by Carlos Coronel – Test Bank
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CHAPTER 3: THE RELATIONAL DATABASE MODEL
1. The
practical significance of taking the logical view of a database is that it
serves as a reminder of the simple file concept of data storage.
a. True
b. False
ANSWER: True
2. You
can think of a table as a persistent representation of a logical relation.
a. True
b. False
ANSWER: True
3. The
order of the rows and columns is important to the DBMS.
a. True
b. False
ANSWER: False
4. Character
data can contain any character or symbol intended for mathematical
manipulation.
a. True
b. False
ANSWER: False
5. The
row’s range of permissible values is known as its domain.
a. True
b. False
ANSWER: False
6. Each
table in a relational database must have a primary key.
a. True
b. False
ANSWER: True
7. The
idea of determination is unique to the database environment.
a. True
b. False
ANSWER: False
8. Only
a single attribute, not multiple attributes, can define functional dependence.
a. True
b. False
ANSWER: False
9. If
the attribute (B) is functionally dependent on a composite key (A) but not on
any subset of that composite key, the attribute (B) is fully functionally
dependent on (A).
a. True
b. False
ANSWER: True
10. A
null is created when you press the Enter key or the Tab key to move to the next
entry without making a prior entry of any kind.
a. True
b. False
ANSWER: True
11. Depending
on the sophistication of the application development software, nulls can create
problems when functions such as COUNT, AVERAGE, and SUM are used.
a. True
b. False
ANSWER: True
12. RDBMSs
enforce integrity rules automatically.
a. True
b. False
ANSWER: True
13. Relational
algebra defines the theoretical way of manipulating table contents using
relational operators.
a. True
b. False
ANSWER: True
14. The
SELECT operator yields a vertical subset of a table.
a. True
b. False
ANSWER: False
15. The
DIFFERENCE operator subtracts one table from the other.
a. True
b. False
ANSWER: True
16. In a
natural join, the column on which the join was made occurs twice in the new
table.
a. True
b. False
ANSWER: False
17. The
DIVIDE operation uses one singlecolumn table (e.g., column “a”) as the divisor
and one twocolumn table (e.g., columns “a” and “b”) as the dividend.
a. True
b. False
ANSWER: True
18. A
data dictionary is sometimes described as “the database designer’s database”
because it records the design
decisions about tables and their structures.
1. True
2. False
ANSWER: True
19. The onetomany
(1:M) relationship is easily implemented in the relational model by putting the
foreign key of the “1” side in the table of the “many” side as a primary key.
a. True
b. False
ANSWER: False
20. As
rare as 1:1 relationships should be, certain conditions absolutely require
their use.
a. True
b. False
ANSWER: True
21. logic,
used extensively in mathematics, provides a framework in which an assertion
(statement of fact) canbe verified as either true or false.
a. Predicate
Database
b. Relational
d. Index
ANSWER: a
22. Each
table represents an attribute.
a. column
row
b. dimension
d. value
ANSWER: a
23. Date
attributes contain calendar dates stored in a special format known as the date
format.
a. Epoch
calendar
b. Julian
d. logical
ANSWER: c
24. In
the relational model, are important because they are used to ensure
that each row in a table is uniquelyidentifiable.
a. relations
keys
b. indexes
d. logical structures
ANSWER: b
25. A is
any key that uniquely identifies each row.
a. superkey
special key
b. foreign
key d. candidate key
ANSWER: a
26. A key
can be described as a minimal superkey, a superkey without any unnecessary
attributes.
a. secondary
candidate
b. primary
d. foreign
ANSWER: b
27. A is
the primary key of one table that has been placed into another table to create
a common attribute.
a. superkey
composite primary key
b. candidate
key d. foreign key
ANSWER: d
28. Referential dictates
that the foreign key must contain values that match the primary key in the
related table,or must contain null.
a. integrity
uniqueness
b. model
d. attribute
ANSWER: a
29. A key
is defined as a key that is used strictly for data retrieval purposes.
a. lookup
foreign
b. candidate
d. secondary
ANSWER: d
30. The
CUSTOMER table’s primary key is CUS_CODE. The CUSTOMER primary key column has
no null entries, and all entries are unique. This is an example of
a. entity
referential
b. relational
d. null
ANSWER: a
31. The constraint
can be placed on a column to ensure that every row in the table has a value for
that column.
a. UNIQUE
NOT NULL
b. VALUE
d. EMPTY
ANSWER: b
32. To be
considered minimally relational, the DBMS must support the key relational
operators , PROJECT, andJOIN.
a. INTERSECT
UNION
b. DIFFERENCE
d. SELECT
ANSWER: d
33. ,
also known as RESTRICT, yields values for all rows found in a table that
satisfy a given condition.
a. INTERSECT
UNION
b. DIFFERENCE
d. SELECT
ANSWER: d
34. returns
only the attributes requested, in the order in which they are requested.
a. PROJECT
SELECT
b. UNION
d. DIFFERENCE
ANSWER: a
35. When
two or more tables share the same number of columns, and when their
corresponding columns share the sameor compatible domains, they are said to be .
a. intersect-compatible
union-compatible
b. difference-compatible
d. select-compatible
ANSWER: b
36. A(n) join
links tables by selecting only the rows with common values in their common
attribute(s).
a. attribute
unique
b. foreign
d. natural
ANSWER: d
37. are
especially useful when you are trying to determine what values in related
tables cause referential integrityproblems.
a. Inner
joins
b. Outer
joins
c. Equijoins
d. Theta
joins
ANSWER: b
38. A(n) only
returns matched records from the tables that are being joined.
a. outer
join inner join
b. equijoin
d. theta join
ANSWER: b
39. A contains
at least all of the attribute names and characteristics for each table in the
system.
a. data
dictionary relational schema
b. logical
schema d. database
ANSWER: a
40. The is
actually a system-created database whose tables store the user/designer-created
databasecharacteristics and contents.
a. database
tuple systematic database
b. unique
index d. system catalog
ANSWER: d
41. In a
database context, the word indicates the use of the same attribute
name to label different attributes.
a. redundancy
homonym
b. duplicate
d. synonym
ANSWER: b
42. In a database
context, a(n) indicates the use of different names to describe the
same attribute.
a. entity
duplicate
b. synonym
d. homonym
ANSWER: c
43. The relationship
is the “relational model ideal.”
44. 1:1
b. 1:M
45. M:1
d. M:N
ANSWER: b
44. The relationship
should be rare in any relational database design.
45. 1:1
b. 1:M
46. M:1
d. M:N
ANSWER: a
45. relationships
can be implemented by creating a new entity in 1:M relationships with the
original entities.
a. 1:N
M:1
b. M:N
d. 1:1
ANSWER: c
46. Another
name for a composite entity is a(n)
a. bridge
linked
b. directive
d. associative
ANSWER: a
47. A(n) is
an orderly arrangement used to logically access rows in a table.
a. primary
rule superkey
b. relationship
d. index
ANSWER: d
48. When
you define a table’s primary key, the DBMS automatically creates a(n) index
on the primary key column(s) you declared.
a. key
composite
b. unique
d. primary
ANSWER: c
49. According
to Codd’s rule of relational database, “Application programs and ad
hoc facilities are logicallyunaffected when changes are made to the table
structures that preserve the original table values (changing order ofcolumns or
inserting columns).”
a. nonsubversion
logical data independence
b. comprehensive
data sublanguage d. integrity independence
ANSWER: b
50. According
to Codd’s rule of relational database, “If the system supports lowlevel
access to the data, users must not be allowed to bypass the integrity rules of
the database.”
a. nonsubversion
rule zero
b. view
updating d. information
ANSWER: a
51. A
table is also called a(n) because the relational model’s creator,
E. F. Codd, used the two terms as synonyms.
ANSWER: relation
52. In a
relational table, each column has a specific range of values known as the
ANSWER: attribute
53. In a relational
model, are also used to establish relationships among tables and to
ensure the integrity of thedata.
ANSWER: keys
54. A
primary key is a(n) key chosen to be the primary means by which
rows of a table are uniquely identified.
ANSWER: candidate
55. To
avoid nulls, some designers use special codes, known as , to
indicate the absence of some value.
ANSWER: flags
56. The
relational operators have the property of ; that is, the use of
relational algebra operators on existingrelations (tables) produces new
relations.
ANSWER: closure
57. PRODUCT
yields all possible pairs of rows from two tables, also known as the
ANSWER: Cartesian
58. is
the real power behind the relational database, allowing the use of independent
tables linked by commonattributes.
ANSWER: JOIN
59. A(n) links
tables on the basis of an equality condition that compares specified columns of
each table.
ANSWER: equijoin
60. A(n) provides
a detailed description of all tables found within the user/designer-created
database.
ANSWER: data dictionary
61. The catalog
can be described as a detailed system data dictionary that describes all
objects within thedatabase, including data about table names, the table’s
creator and creation date, the number of columns in eachtable, the data type
corresponding to each column, index filenames, index creators, authorized
users, and accessprivileges.
ANSWER: system
62. The relationship
is the relational database norm.
ANSWER: 1:M
63. relationships
cannot be implemented as such in the relational model.
ANSWER: M:N
64. If
one department chair—a professor—can chair only one department, and one
department can have only one department chair. The entities PROFESSOR and
DEPARTMENT exhibit a(n)
ANSWER: 1:1
65. One
characteristic of generalization hierarchies is that they are implemented as
ANSWER: 1:1
66. The
proper use of keys is crucial to controlling data redundancy.
ANSWER: foreign
67. Proper
data design requires carefully defined and controlled data
redundancies to function properly.
ANSWER: warehousing
68. A(n) index
is an index in which the index key can have only one pointer value (row)
associated with it.
ANSWER: unique
69. An
index key can have multiple (a composite index).
ANSWER: attributes
70. Codd’s rule
of relational database states that every value in a table is guaranteed to be
accessible through a combination of table name, primary key value, and column
name.
ANSWER: Guaranteed Access
71. What
is a key and how is it important in a relational model?
ANSWER: In a relational model, keys are
important because they are used to ensure that each row in a table isuniquely
identifiable. They are also used to establish relationships among tables and to
ensure theintegrity of the data. A key consists of one or more attributes that
determine other attributes. Forexample, an invoice number identifies all of the
invoice attributes, such as the invoice date and thecustomer name.
72. Define
entity integrity. What are the two requirements to ensure entity integrity?
ANSWER: Entity integrity is the
condition in which each row (entity instance) in the table has its own
uniqueidentity. To ensure entity integrity, the primary key has two
requirements:
·
all of the values in the primary key must be unique.
·
no key attribute in the primary key can contain a null.
73. Describe
the use of null values in a database.
ANSWER: Null values are problematic
in a relational model. A null is the absence of any data value, and it is
neverallowed in any part of the primary key. From a theoretical perspective, it
can be argued that a table thatcontains a null is not properly a relational
table at all. From a practical perspective, however, some nullscannot be
reasonably avoided. For example, not all students have a middle initial. As a
general rule, nullsshould be avoided as much as reasonably possible. In fact,
an abundance of nulls is often a sign of a poordesign. Also, nulls should be
avoided in the database because their meaning is not always identifiable.
For example, a null could represent:
·
An unknown attribute value.
·
A known, but missing, attribute value.
·
A “not applicable” condition.
74. Describe
the use of the INTERSECT operator.
ANSWER: INTERSECT yields only
the rows that appear in both tables. As with UNION, the tables must be
union-compatible to yield valid results. For example, you cannot use INTERSECT
if one of the attributes isnumeric and one is character-based. For the rows to
be considered the same in both tables and appear inthe result of the INTERSECT,
the entire rows must be exact duplicates.
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