ssd7exam2choice.txt

卡耐基课程 ssd7 exam2 选择题及其答案

 2. 
 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) I and II
 (c) I only
 (d) II only  

 Correct answer is  (a)  

 Your score on this question is: 10.00  

 Feedback: 
   
See section 3.3.1, subsection "Functional Dependencies," in the course notes.
 
 

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 3. 
 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) II and III only
 (d) I and II 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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 4. 
 Through normalization, data redundancy  
 

  (a) can be eliminated
 (b) can be maximized
 (c) can be minimized but not eliminated
 (d) are usually left unchanged  

 Correct answer is  (a)  

 Your score on this question is: 10.00  
 

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 5. 
 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) Each normal form contains a state of independent properties, unrelated to other normal forms.
 (c) Schemas that are in second normal form are considered the best.
 (d) The lower the normal form number, the better the schema design is.  

 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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 6. 
 For a relation to be in 3NF, it should not contain _____ attribute that is transitively dependent on _____.  
 

  (a) a primary key, a foreign key
 (b) a primary key, a non-primary key
 (c) a non-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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 7. 
 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, removed from
 (b) at least one, removed from
 (c) at least one, added to
 (d) no, added to  

 Correct answer is  (a)  

 Your score on this question is: 10.00  
 

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 8. 
 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) I, II and III
 (b) None
 (c) I and II only
 (d) I only  

 Correct answer is  (c)  

 Your score on this question is: 10.00  

 Feedback: 
   
See section 3.3.2 in the course notes.
 
 

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 9. 
 For a relation to be in 2NF, _____ attribute must be fully functionally dependent on _____.  
 

  (a) every alternate key, the primary key
 (b) every non-key, at least one key
 (c) every non-key, every key
 (d) every non-primary-key, the primary key  

 Correct answer is  (d)  

 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) no, added to
 (b) no, removed from
 (c) at least one, added to
 (d) at least one, removed from  

 Correct answer is  (d)  
1. 
 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 relationship that identifies a strong entity's owner
 (d) The entity upon which a strong entity's existence depends  

 You did not answer this question. 

 Correct answer is  (a)  

 Your score on this question is: 0.00  
 

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 2. 
 In an ER model, the cardinality ratio of a relationship type is  
 

  (a) the minimum number of entities that can participate in that relationship type
 (b) the number of instances of relationships of that relationship type
 (c) the number of entity types involved in that relationship type
 (d) the number of relationships of that relationship type in which an entity can participate  

 You did not answer this question. 

 Correct answer is  (d)  

 Your score on this question is: 0.00  
 

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 3. 
 In the Entity-Relationship model, properties that characterize entities and relationships are modeled as  
 

  (a) entity types
 (b) participation constraints
 (c) weak entities
 (d) attributes  

 You did not answer this question. 

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   
See section 3.2.1, subsection "Attributes," in the course notes.
 
 

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 4. 
 In an ER model, what is a recursive relationship type?  
 

  (a) A never-ending type of relationship
 (b) The relationship type where the related entities are one and the same
 (c) The type of relationship between entities of one entity type
 (d) The type of relationship that does not belong anywhere  

 You did not answer this question. 

 Correct answer is  (c)  

 Your score on this question is: 0.00  
 

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 5. 
 In the Entity-Relationship model, a derived attribute is one  
 

  (a) that characterizes a relationship instead of an entity
 (b) that may have multiple values simultaneously
 (c) whose value can be computed from the values of other attributes
 (d) that is composed of multiple atomic attributes  

 You did not answer this question. 

 Correct answer is  (c)  

 Your score on this question is: 0.00  

 Feedback: 
   
See section 3.2.1, subsection "Attributes," in the course notes.
 
 

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 6. 
 In the Entity-Relationship model, the degree of a relationship specifies which of the following?  
 

  (a) The number of attributes that characterize the relationship
 (b) The number of entities that participate in the relationship
 (c) The cardinality ratio of the relationship
 (d) The number of integrity constraints required to implement the relationship  

 You did not answer this question. 

 Correct answer is  (b)  

 Your score on this question is: 0.00  

 Feedback: 
   
See section 3.2.1, subsection "Entities and Relationships," in the course notes.
 
 

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 7. 
 Which of the following is true about storage for derived attributes?  
 

  (a) Derived attributes are usually not stored because they can be computed.
 (b) Derived attributes are usually stored because storage improves retrieval performance.
 (c) Derived attributes must be stored.
 (d) Derived attributes must not be stored.  

 You did not answer this question. 

 Correct answer is  (a)  

 Your score on this question is: 0.00  
 

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 8. 
 In EER modeling, generalization is the process of generating  
 

  (a) superclasses out of subclasses
 (b) entities out of attributes
 (c) subclasses out of superclasses
 (d) attributes out of entities  

 You did not answer this question. 

 Correct answer is  (a)  

 Your score on this question is: 0.00  
 

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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) table
 (c) row
 (d) column  

 You did not answer this question. 

 Correct answer is  (b)  

 Your score on this question is: 0.00  
 

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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) II only
 (b) I only
 (c) Both I and II
 (d) Neither I nor II  

 You did not answer this question. 

 Correct answer is  (d)  


 1. 
 Which of the following is true about storage for derived attributes?  
 

  (a) Derived attributes are usually stored because storage improves retrieval performance.
 (b) Derived attributes must be stored.
 (c) Derived attributes are usually not stored because they can be computed.
 (d) Derived attributes must not be stored.  

 You did not answer this question. 

 Correct answer is  (c)  

 Your score on this question is: 0.00  
 

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 2. 
 In an ER model, the cardinality ratio of a relationship type is  
 

  (a) the minimum number of entities that can participate in 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 number of instances of relationships of that relationship type  

 You did not answer this question. 

 Correct answer is  (c)  

 Your score on this question is: 0.00  
 

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 3. 
 In the Entity-Relationship model, the degree of a relationship specifies which of the following?  
 

  (a) The number of attributes that characterize the relationship
 (b) The number of integrity constraints required to implement the relationship
 (c) The cardinality ratio of the relationship
 (d) The number of entities that participate in the relationship  

 You did not answer this question. 

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   
See section 3.2.1, subsection "Entities and Relationships," in the course notes.
 
 

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 4. 
 In the Entity-Relationship model, properties that characterize entities and relationships are modeled as  
 

  (a) weak entities
 (b) participation constraints
 (c) attributes
 (d) entity types  

 You did not answer this question. 

 Correct answer is  (c)  

 Your score on this question is: 0.00  

 Feedback: 
   
See section 3.2.1, subsection "Attributes," in the course notes.
 
 

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 5. 
 A weak entity type implies a  
 

  (a) weak relationship type
 (b) relationship with total participation constraint
 (c) strong relationship type
 (d) relationship with partial participation constraint  

 You did not answer this question. 

 Correct answer is  (b)  

 Your score on this question is: 0.00  
 

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 6. 
 In an ER model, which of the following is true about a component attribute?  
 

  (a) A component attribute can be a composite attribute.
 (b) Component attributes must always be combined by an aggregation operation.
 (c) A component attribute always contains other components.
 (d) A component attribute is always atomic.  

 You did not answer this question. 

 Correct answer is  (a)  

 Your score on this question is: 0.00  
 

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 7. 
 In the Entity-Relationship model, a derived attribute is one  
 

  (a) that characterizes a relationship instead of an entity
 (b) that is composed of multiple atomic attributes
 (c) whose value can be computed from the values of other attributes
 (d) that may have multiple values simultaneously  

 You did not answer this question. 

 Correct answer is  (c)  

1. 
 Through normalization, update anomalies  
 

  (a) is usually left unchanged
 (b) can be minimized but not eliminated
 (c) can be maximized
 (d) can be eliminated  

 You did not answer this question. 

 Correct answer is  (d)  

 Your score on this question is: 0.00  
 

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 2. 
 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) II only
 (d) I, II, and III  

 You did not answer this question. 

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   
See section 3.3.1 in the course notes.
 
 

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 3. 
 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) I only
 (b) I and II
 (c) II only
 (d) None