?? ssd7exam2choice.txt
字號:
1.
In the Entity-Relationship model, the degree of a relationship specifies which of the following?
(a) The cardinality ratio of the relationship
(b) The number of integrity constraints required to implement the relationship
(c) The number of attributes that characterize the relationship
(d) The number of entities that participate in the relationship
Correct answer is (d)
Your score on this question is: 10.00
Feedback:
See section 3.2.1, subsection "Entities and Relationships," in the course notes.
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2.
In an ER model, which of the following is true about a component attribute?
(a) A component attribute is always atomic.
(b) Component attributes must always be combined by an aggregation operation.
(c) A component attribute can be a composite attribute.
(d) A component attribute always contains other components.
Correct answer is (c)
Your score on this question is: 10.00
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3.
In the Entity-Relationship model, properties that characterize entities and relationships are modeled as
(a) attributes
(b) participation constraints
(c) entity types
(d) weak entities
Correct answer is (a)
Your score on this question is: 10.00
Feedback:
See section 3.2.1, subsection "Attributes," in the course notes.
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4.
What is an identifying owner in an ER model?
(a) The entity upon which a weak entity's existence depends
(b) The relationship that identifies a weak entity's owner
(c) The entity upon which a strong entity's existence depends
(d) The relationship that identifies a strong entity's owner
Correct answer is (a)
Your score on this question is: 10.00
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5.
In an ER model, the cardinality ratio of a relationship type is
(a) the number of instances of relationships of that relationship type
(b) the number of entity types involved in that relationship type
(c) the number of relationships of that relationship type in which an entity can participate
(d) the minimum number of entities that can participate in that relationship type
Correct answer is (c)
Your score on this question is: 10.00
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6.
Which of the following is true about storage for derived attributes?
(a) Derived attributes must not be stored.
(b) Derived attributes are usually stored because storage improves retrieval performance.
(c) Derived attributes must be stored.
(d) Derived attributes are usually not stored because they can be computed.
Correct answer is (d)
Your score on this question is: 10.00
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7.
In an ER model, what is a recursive relationship type?
(a) A never-ending type of relationship
(b) The type of relationship that does not belong anywhere
(c) The type of relationship between entities of one entity type
(d) The relationship type where the related entities are one and the same
Correct answer is (c)
Your score on this question is: 10.00
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8.
In EER modeling, generalization is the process of generating
(a) superclasses out of subclasses
(b) subclasses out of superclasses
(c) entities out of attributes
(d) attributes out of entities
Correct answer is (a)
Your score on this question is: 10.00
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9.
When mapping from an ER model to a relational model, a strong entity is mapped into a
(a) table
(b) row
(c) column
(d) key
Correct answer is (a)
Your score on this question is: 10.00
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10.
Which of the following is true about attributes in a relational model?
Attributes can be multi-valued.
Attributes can be composite.
(a) Both I and II
(b) II only
(c) Neither I nor II
(d) I only
Correct answer is (c)
1.
In an ER model, what is a recursive relationship type?
(a) The relationship type where the related entities are one and the same
(b) The type of relationship that does not belong anywhere
(c) The type of relationship between entities of one entity type
(d) A never-ending type of relationship
Correct answer is (c)
Your score on this question is: 10.00
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2.
In an ER model, the cardinality ratio of a relationship type is
(a) the number of relationships of that relationship type in which an entity can participate
(b) the minimum number of entities that can participate in that relationship type
(c) the number of entity types involved in that relationship type
(d) the number of instances of relationships of that relationship type
Correct answer is (a)
Your score on this question is: 10.00
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3.
In the Entity-Relationship model, a derived attribute is one
(a) that is composed of multiple atomic attributes
(b) that characterizes a relationship instead of an entity
(c) that may have multiple values simultaneously
(d) whose value can be computed from the values of other attributes
Correct answer is (d)
Your score on this question is: 10.00
Feedback:
See section 3.2.1, subsection "Attributes," in the course notes.
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4.
In the Entity-Relationship model, properties that characterize entities and relationships are modeled as
(a) entity types
(b) weak entities
(c) attributes
(d) participation constraints
Correct answer is (c)
Your score on this question is: 10.00
Feedback:
See section 3.2.1, subsection "Attributes," in the course notes.
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5.
Which of the following is true about storage for derived attributes?
(a) Derived attributes must be stored.
(b) Derived attributes are usually stored because storage improves retrieval performance.
(c) Derived attributes must not be stored.
(d) Derived attributes are usually not stored because they can be computed.
Correct answer is (d)
Your score on this question is: 10.00
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6.
What is an identifying owner in an ER model?
(a) The relationship that identifies a weak entity's owner
(b) The relationship that identifies a strong entity's owner
(c) The entity upon which a strong entity's existence depends
(d) The entity upon which a weak entity's existence depends
Correct answer is (d)
Your score on this question is: 10.00
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7.
In an ER model, which of the following is true about a component attribute?
(a) A component attribute always contains other components.
(b) A component attribute can be a composite attribute.
(c) A component attribute is always atomic.
(d) Component attributes must always be combined by an aggregation operation.
Correct answer is (b)
Your score on this question is: 10.00
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8.
In EER modeling, generalization is the process of generating
(a) attributes out of entities
(b) superclasses out of subclasses
(c) subclasses out of superclasses
(d) entities out of attributes
Correct answer is (b)
Your score on this question is: 10.00
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9.
When mapping from an ER model to a relational model, a strong entity is mapped into a
(a) key
(b) row
(c) column
(d) table
Correct answer is (d)
Your score on this question is: 10.00
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10.
Which of the following is true about attributes in a relational model?
Attributes can be multi-valued.
Attributes can be composite.
(a) I only
(b) II only
(c) Neither I nor II
(d) Both I and II
Correct answer is (c)
1.
Through normalization, update anomalies
(a) can be eliminated
(b) is usually left unchanged
(c) can be maximized
(d) can be minimized but not eliminated
Correct answer is (a)
Your score on this question is: 10.00
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2.
Which of the following is a property (are properties) exhibited by good relational schemas?
The use of null values in tuples
The grouping of as many attributes as possible into one main table
The elimination of data redundancy to avoid update anomalies
(a) III only
(b) None
(c) I and II only
(d) II and III only
Correct answer is (a)
Your score on this question is: 10.00
Feedback:
See section 3.3.1 in the course notes.
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3.
Which of the following statements concerning normal forms is true?
(a) A relation that is in second normal form is also in first normal form.
(b) The lower the normal form number, the better the schema design is.
(c) Each normal form contains a state of independent properties, unrelated to other normal forms.
(d) Schemas that are in second normal form are considered the best.
Correct answer is (a)
Your score on this question is: 10.00
Feedback:
See section 3.3.1 in the course notes.
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4.
Consider the following functional dependency.
{A, B} -> {C}
Regarding this dependency, which of the following statements is (are) true?
The values of C are uniquely determined by the values of A.
The values of A are uniquely determined by the values of C.
(a) None
(b) II only
(c) I only
(d) I and II
Correct answer is (a)
Your score on this question is: 0.00
Feedback:
See section 3.3.1, subsection "Functional Dependencies," in the course notes.
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5.
Which of the following problems can be caused by data redundancy in a relational schema?
Inefficient use of space
Update anomalies and possible loss of data
Inefficient use of processing time
(a) I and II only
(b) I and III only
(c) I, II, and III
(d) II only
Correct answer is (c)
Your score on this question is: 10.00
Feedback:
See section 3.3.1 in the course notes.
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6.
Consider a table with atomic attributes A, B, and C and the following functional dependencies.
A -> B
B -> C
If the primary key of this table is attribute A, then this relation satisfies which of the following normal forms?
First
Second
Third
(a) None
(b) I only
(c) I, II and III
(d) I and II only
Correct answer is (d)
Your score on this question is: 10.00
Feedback:
See section 3.3.2 in the course notes.
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7.
For a relation to be in 3NF, it should not contain _____ attribute that is transitively dependent on _____.
(a) a non-primary key, a foreign key
(b) a primary key, a non-primary key
(c) a primary key, a foreign key
(d) a non-primary key, the primary key
Correct answer is (d)
Your score on this question is: 10.00
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8.
The FD X -> Y is a full dependency in a relation R, if there is _____ attribute A that can be _____ X and the dependency still holds.
(a) no, added to
(b) no, removed from
(c) at least one, removed from
(d) at least one, added to
Correct answer is (b)
Your score on this question is: 10.00
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9.
For a relation to be in 2NF, _____ attribute must be fully functionally dependent on _____.
(a) every non-primary-key, the primary key
(b) every alternate key, the primary key
(c) every non-key, every key
(d) every non-key, at least one key
Correct answer is (a)
Your score on this question is: 10.00
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10.
The FD X -> Y is a partial dependency in a relation R, if there is _____ attribute A that can be _____ X and the dependency still holds.
(a) at least one, removed from
(b) at least one, added to
(c) no, added to
(d) no, removed from
Correct answer is (a)
Your score on this question is: 10.00
1.
Through normalization, update anomalies
(a) can be eliminated
(b) is usually left unchanged
(c) can be minimized but not eliminated
(d) can be maximized
Correct answer is (a)
Your score on this question is: 10.00
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