潜龙勿用1.txt

ssd7数据库练习选择题1-4答案

Your performance was as follows: 

 You took 14 minutes on this assessment from Sat Jul 7 08:59:08 UTC+0800 2007 to Sat Jul 7 09:12:20 UTC+0800 2007. 

 Total score: 100.00 
 
 

 

 1. 
 A collision occurs in hashing when the bucket in which the record to be _____  
 

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

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 



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 2. 
 In a two-phase locking protocol, a transaction _____ downgrade a write lock to a read lock _____.  
 

  (a) cannot, in the growing phase only
 (b) can, under all circumstances
 (c) can, in the shrinking phase only
 (d) cannot, under any circumstances  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

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 3. 
 Which of the following is true about compensating transactions?  
 

  (a) The DBMS can automatically write compensating transactions.
 (b) The DBMS will automatically write a compensating transaction for each committed transaction.
 (c) The DBMS cannot automatically write compensating transactions.
 (d) The user can request the DBMS to write compensating transactions automatically.  

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

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 4. 
 A deadlock occurs when  
 

  (a) an aborted transaction holding a lock is restarted
 (b) 2 or more transactions wait indefinitely because each holds the data items of another
 (c) a transaction holding a lock is aborted
 (d) a transaction is aborted and restarted repeatedly  

 Correct answer is  (b)  

 Your score on this question is: 5.00  
 

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 5. 
 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) Transactions either complete, committing all changes to the DBMS, or rollback, resetting the DBMS to a state just prior to a transaction's execution.
 (c) A transaction is partially done if the system crashes in the middle of its execution.
 (d) 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.  

 Correct answer is  (b)  

 Your score on this question is: 5.00  
 

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 6. 
 Which of the following will a good hash function do?  
 

  (a) leave gaps in the file at periodic intervals for future growth
 (b) concentrate keys in one location
 (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  
 

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 7. 
 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 ends shortly after the start of the transaction when all locks for the transaction must be acquired.
 (b) The growing phase must be in the first half of the transaction and the shrinking phase must be in the second half.
 (c) There is a plateau phase when locks are neither released nor acquired; this phase comes between the growing phase and the shrinking phase.
 (d) The growing phase ends just before commit.  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

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 8. 
 A shared lock on a data item represents permission to perform which of the operations, read and write, on the data item?  
 

  (a) Both read and write
 (b) Neither read nor write
 (c) Write only
 (d) Read only  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

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 9. 
 Which concurrency control protocols perform best in all situations?  
 

  (a) optimistic protocols
 (b) two-phase locking protocols
 (c) pessimistic protocols
 (d) none  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 

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 10. 
 The undo action undoes the effects of a(n) _____ transaction, and the redo action redoes the effects of a(n) _____ transaction.  
 

  (a) aborted, aborted
 (b) aborted, committed
 (c) committed, committed
 (d) committed, aborted  

 Correct answer is  (b)  

 Your score on this question is: 5.00  
 

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 11. 
 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) II only
 (b) I and II
 (c) I 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.
 
 

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 12. 
 What is a roll-up operation in a data warehouse application?  
 

  (a) Viewing along a different dimension
 (b) Deriving a fine-grained view, i.e., a disaggregated view along a particular dimension
 (c) Deriving a coarse-grained view, i.e., a summarized view along a particular dimension
 (d) Condensing the view in all the dimensions  

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

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 13. 
 In a hierarchical database, data records are represented using which of the following data structures?  
 

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

 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.
 
 

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 14. 
 In a network database, data records are represented using which of the following data structures?  
 

  (a) Arrays
 (b) Hash tables
 (c) Matrices
 (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.
 
 

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 15. 
 Which of the following collections allows duplicate elements? 
set 
multiset 
list 
 
 

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

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

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 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.
 
 

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 17. 
 In a network database, the first record of an ordered linked list that represents a one-to-many relationship is called a(n)  
 

  (a) vector
 (b) intermediary
 (c) link
 (d) owner  

 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.
 
 

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 18. 
 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)  

 Your score on this question is: 5.00  

 Feedback: 
   
5.2#Issues and Categories of Data Warehouses
 
 

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 19. 
 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 and II only
 (d) I, II, and III  

 Correct answer is  (c)  

 Your score on this question is: 5.00  

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

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 20. 
 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.
 
 

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 Go to top of assessment.  

 Total score: 100.00 

 ? Copyright 2004 iCarnegie, Inc. All rights reserved.  
Your performance was as follows: 

 You took 19 minutes on this assessment from Sat Jul 7 09:02:46 UTC+0800 2007 to Sat Jul 7 09:20:52 UTC+0800 2007. 

 Total score: 80.00 
 
 

 

 1. 
 A deadlock occurs when  
 

  (a) a transaction is aborted and restarted repeatedly
 (b) an aborted transaction holding a lock is restarted
 (c) a transaction holding a lock is aborted
 (d) 2 or more transactions wait indefinitely because each holds the data items of another  

 Correct answer is  (d)  

 Your score on this question is: 5.00  
 



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 2. 
 Hash files use a hash function to map a _____ to a(n) _____  
 

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

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

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 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 is full
 (c) stored is full
 (d) deleted has exactly one record  

 Correct answer is  (c)  

 Your score on this question is: 0.00  
 

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 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) all the fields are indexed
 (d) the records are stored in the descending order of the primary key  

 Correct answer is  (c)  

 Your score on this question is: 0.00  
 

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 5. 
 In a two-phase locking protocol, a transaction _____ upgrade a read lock to a write lock _____.  
 

  (a) cannot, under any circumstances
 (b) cannot, in the shrinking phase o
 (c) can, in the growing phase only
 (d) can, under all circumstances  

 Correct answer is  (c)  

 Your score on this question is: 5.00  
 

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 6. 
 In a two-phase locking protocol, a transaction _____ downgrade a write lock to a read lock _____.  
 

  (a) cannot, in the growing phase only
 (b) can, in the shrinking phase only
 (c) cannot, under any circumstances
 (d) can, under all circumstances  

 Correct answer is  (c)  

 Your score on this question is: 0.00  
 

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 7. 
 Hashing works best for which of the following searches? 
equality searches 
range searches 
substring searches