ssd7exam2choice.txt

ssd7选择题答案

1. 
 In the Entity-Relationship model, the degree of a relationship specifies which of the following?  
 (d) The number of entities that participate in the relationship  
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 2. 
 In an ER model, which of the following is true about a component attribute?  
 (c) A component attribute can be a composite attribute.
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 3. 
 In the Entity-Relationship model, properties that characterize entities and relationships are modeled as  
  (a) attributes
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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
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 5. In an ER model, the cardinality ratio of a relationship type is  
 (c) the number of relationships of that relationship type in which an entity can participate
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 6. Which of the following is true about storage for derived attributes?  
 (d) Derived attributes are usually not stored because they can be computed.  
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 7. In an ER model, what is a recursive relationship type?  
 (c) The type of relationship between entities of one entity type
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 8. In EER modeling, generalization is the process of generating  
(a) superclasses out of subclasses
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9. When mapping from an ER model to a relational model, a strong entity is mapped into a  
  (a) table
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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. 
(c) Neither I nor II
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 3. In the Entity-Relationship model, a derived attribute is one  
 (d) whose value can be computed from the values of other attributes 
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1. Through normalization, update anomalies  
(a) can be eliminated
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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
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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.
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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
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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 
(c) I, II, and III
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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 
(d) I and II only  
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7. For a relation to be in 3NF, it should not contain _____ attribute that is transitively dependent on _____.  
(d) a non-primary key, the primary key  
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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.  
 (b) no, removed from
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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
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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
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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. 
 (d) Neither I nor II  
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5. A weak entity type implies a  
 (b) relationship with total participation constraint
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1. In an ER model, which of the following is true about a composite attribute?  
(c) A composite attribute can be broken into more basic attributes.
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2. The term physical data independence refers to the ability to change  
(a) the physical layout of the data without changing the external schemas, the conceptual schemas, or the application programs
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3. What attributes does a subclass have?  
 (b) All the attributes of its superclass, and possibly more
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4. If X -> Y, which of the following would make Y fully dependent on X?  
 (b) X is a single attribute
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6. Database design typically consists of which of the following phases?
Conceptual design 
Logical design 
Physical design 
 (b) I, II, and III
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7. A relational schema is in first normal form, if the domain of all of its  
(d) attributes can take on only atomic values  
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8. In an ER model, a derived attribute is one whose values  
(b) can be derived from the values of some other attributes
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9. Y is transitively dependent on X, if  
(b) X -> A, B and A -> Y
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10. Relationships in an ER model are primarily translated to which of the following in a relational model?  
 (b) primary keys and foreign keys