Distributed Databases Questions and Answers

Q: In a semijoin, only the joining attribute is sent from one site to another, and then only the required rows are returned.

Correct answer: TrueThis is the definition. The joining attribute alone is sent to the other site, which matches it against its own rows and returns only those that participate in the join. The saving comes from restricting both what is sent and what comes back, and it is what makes distributed joins practicable over a slow link.

Q: A transaction manager is which of the following?

Correct answer: All of the above.The transaction manager is responsible for atomicity and isolation, so it must log what each transaction does, hold the before and after images needed to undo or redo it, and apply the concurrency control that keeps concurrent transactions from interfering. All three are aspects of the same duty.

Q: Location transparency allows for which of the following?

Correct answer: All of the above.Location transparency means nobody has to know where the data physically sits - not the user writing a query, not the programmer writing an application, not the manager reading a report. The system resolves the location, which is what allows data to be moved between sites without changing anything above.

31.

In a semijoin, only the joining attribute is sent from one site to another, and then only the required rows are returned.

A.True
B.False

Answer: A

Correct answer: True

This is the definition. The joining attribute alone is sent to the other site, which matches it against its own rows and returns only those that participate in the join. The saving comes from restricting both what is sent and what comes back, and it is what makes distributed joins practicable over a slow link.

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32.

A transaction manager is which of the following?

A.Maintains a log of transactions
B.Maintains before and after database images
C.Maintains appropriate concurrency control
D.All of the above.

Answer: D

Correct answer: All of the above.

The transaction manager is responsible for atomicity and isolation, so it must log what each transaction does, hold the before and after images needed to undo or redo it, and apply the concurrency control that keeps concurrent transactions from interfering. All three are aspects of the same duty.

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33.

Location transparency allows for which of the following?

A.Users to treat the data as if it is at one location
B.Programmers to treat the data as if it is at one location
C.Managers to treat the data as if it is at one location
D.All of the above.

Answer: D

Correct answer: All of the above.

Location transparency means nobody has to know where the data physically sits - not the user writing a query, not the programmer writing an application, not the manager reading a report. The system resolves the location, which is what allows data to be moved between sites without changing anything above.

Discuss in Forum

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Distributed Databases Questions and Answers

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