潜龙勿用1.txt

ssd7数据库练习选择题1-4答案

 
 

--------------------------------------------------------------------------------

 14. 
 To retrieve data from a hierarchical database, program logic for performing _____ must be available.  
 

  (a) navigation
 (b) polymorphism
 (c) relational joins
 (d) decomposition  

 Correct answer is  (a)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Hierarchical Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 15. 
 In a hierarchical database, a single tree can accommodate which of the following types of binary relationships?

One-to-one relationships 
One-to-many relationships 
Many-to-many relationships 
 
 

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

 Correct answer is  (d)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Hierarchical Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 16. 
 In a network database, a binary one-to-many relationship is typically represented using a  
 

  (a) sparse matrix
 (b) linked list
 (c) hash table
 (d) binary tree  

 Correct answer is  (b)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Network Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 17. 
 Small, highly focused databases at the departmental level that are used to build enterprise-wide data warehouses are known as  
 

  (a) data cubes
 (b) hypercubes
 (c) virtual data warehouses
 (d) data marts  

 Correct answer is  (d)  

 Your score on this question is: 5.00  

 Feedback: 
   
5.2#Issues and Categories of Data Warehouses
 
 

--------------------------------------------------------------------------------

 18. 
 Which of the following types of databases store data in tables and represent relationships using foreign keys?  
 

  (a) Relational databases
 (b) Network databases
 (c) Object-oriented databases
 (d) Hierarchical databases  

 Correct answer is  (a)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Relational Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 19. 
 In a network database, data records are represented using which of the following data structures?  
 

  (a) Matrices
 (b) Hash tables
 (c) Arrays
 (d) Graphs  

 Correct answer is  (d)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Network Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 20. 
 Which of the following collections allows duplicate elements? 
set 
multiset 
list 
 
 

  (a) II only
 (b) III only
 (c) II and III only
 (d) I, II, and III  

 Correct answer is  (c)  

 Your score on this question is: 5.00  


Which of the following is true about the effects of a transaction as seen by an external user who does not participate in the transaction?  
 

  (a) During recovery from a crash, the DBMS may decide to undo the effects of a committed transaction and hence the effects will not be seen by the user after the undo.
 (b) During recovery from a crash, the DBMS may decide to redo the effects of an aborted transaction and hence the effects will be seen by the user after the redo.
 (c) Transactions either complete, committing all changes to the DBMS, or rollback, resetting the DBMS to a state just prior to a transaction's execution.
 (d) A transaction is partially done if the system crashes in the middle of its execution.  

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 



--------------------------------------------------------------------------------

 2. 
 Which of the following is true about the growing phase and the shrinking phase of a strict two-phase locking protocol?  
 

  (a) The growing phase must be in the first half of the transaction and the shrinking phase must be in the second half.
 (b) There is a plateau phase when locks are neither released nor acquired; this phase comes between the growing phase and the shrinking phase.
 (c) The growing phase ends shortly after the start of the transaction when all locks for the transaction must be acquired.
 (d) The growing phase ends just before commit.  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 3. 
 A collision occurs in hashing when the bucket in which the record to be _____  
 

  (a) stored has at least one other record
 (b) deleted has exactly one record
 (c) deleted is full
 (d) stored is full  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 4. 
 A file is fully inverted if and only if  
 

  (a) the data files point to the index files
 (b) none of the fields are indexed
 (c) the records are stored in the descending order of the primary key
 (d) all the fields are indexed  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 5. 
 Hashing works best for which of the following searches? 
equality searches 
range searches 
substring searches 
 
 

  (a) I and II only
 (b) II and III only
 (c) I only
 (d) III only  

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 6. 
 Hash files use a hash function to map a _____ to a(n) _____  
 

  (a) hash value, key where the address may be found
 (b) key value, address where the key may be found
 (c) key value, address where the hash value may be found
 (d) hash value, address where the key may be found  

 Correct answer is  (b)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 7. 
 How does linear probing solve the problem of collisions in hashing?  
 

  (a) The hash file is probed linearly from the start to find the first available slot.
 (b) A linear function is used to determine the next spot to search for slots.
 (c) A serial search is performed from the point of collision to find the first available slot.
 (d) The hash file is probed linearly from the end to find the first available slot.  

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 8. 
 An index file is usually used to index ______ of the data file.  
 

  (a) one field
 (b) most fields
 (c) two fields
 (d) all fields  

 Correct answer is  (a)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 9. 
 Which of the following will a good hash function do?  
 

  (a) concentrate keys in one location
 (b) leave gaps in the file at periodic intervals for future growth
 (c) spread keys around the file in heaps
 (d) spread keys around the file as evenly as possible  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 10. 
 In a two-phase locking protocol, what happens when a transaction requests a conflicting lock?  
 

  (a) The transaction immediately acquires the lock from the current lock-holder.
 (b) The transaction is blocked to acquire the lock.
 (c) The transaction proceeds without acquiring the lock.
 (d) The transaction is aborted immediately.  

 Correct answer is  (b)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 11. 
 In a network database, data records are represented using which of the following data structures?  
 

  (a) Hash tables
 (b) Matrices
 (c) Graphs
 (d) Arrays  

 Correct answer is  (c)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Network Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 12. 
 Which of the following types of databases store data in tables and represent relationships using foreign keys?  
 

  (a) Network databases
 (b) Object-oriented databases
 (c) Relational databases
 (d) Hierarchical databases  

 Correct answer is  (c)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Relational Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 13. 
 In a hierarchical database, a single tree can accommodate which of the following types of binary relationships?

One-to-one relationships 
One-to-many relationships 
Many-to-many relationships 
 
 

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

 Correct answer is  (b)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Hierarchical Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 14. 
 To retrieve data from a hierarchical database, program logic for performing _____ must be available.  
 

  (a) relational joins
 (b) polymorphism
 (c) decomposition
 (d) navigation  

 Correct answer is  (d)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Hierarchical Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 15. 
 Which of the following statements is (are) typically true of hierarchical databases?

They are navigated using preorder traversals. 
Their users must be aware of the databases’ internal tree structures. 
 
 

  (a) I only
 (b) I and II
 (c) II only
 (d) None  

 Correct answer is  (b)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Hierarchical Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 16. 
 In a hierarchical database, data records are represented using which of the following data structures?  
 

  (a) Matrices
 (b) Trees
 (c) Hash tables
 (d) Arrays  

 Correct answer is  (b)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Hierarchical Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 17. 
 In a network database, a binary one-to-many relationship is typically represented using a  
 

  (a) binary tree
 (b) sparse matrix
 (c) hash table
 (d) linked list  

 Correct answer is  (d)  

 Your score on this question is: 5.00  

 Feedback: 
   
See section 5.1.3, subsection "Network Data Model," in the course notes.
 
 

--------------------------------------------------------------------------------

 18. 
 Which of the following collections allows duplicate elements? 
set 
multiset 
list 
 
 

  (a) I, II, and III
 (b) II and III only
 (c) III only
 (d) II only  

 Correct answer is  (b)  

 Your score on this question is: 5.00  
 

--------------------------------------------------------------------------------

 19. 
 Small, highly focused databases at the departmental level that are used to build enterprise-wide data warehouses are known as  
 

  (a) virtual data warehouses
 (b) data marts
 (c) hypercubes
 (d) data cubes  

 Correct answer is  (b)