probs18 - ECE456 Solution Sets 18.2 Explain how the...

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ECE456 Solution Sets A. Silberschatz, Database System Concepts , McGraw-Hill 18-1 18.2 Explain how the following differ: fragmentation transparency, replication transparency, and location transparency. Solution: a. With fragmentation transparency, the user of the system is unaware of any fragmentation the system has implemented. A user may formulate queries against global relations and the system will perform the necessary transformation to generate correct output. b. With replication transparency, the user is unaware of any replicated data. The system must prevent inconsistent operations on the data. This requires more complex concurrency control algorithms. c. Location transparency means the user is unaware of where data are stored. The system must route data requests to the appropriate sites. 18.4 When is it useful to have replication or fragmentation of data? Explain your answer. Solution: Replication is useful when there are many read-only transactions at different sites wanting access to the same data. They can all execute quickly in parallel, accessing local data. But updates become difficult with replication. Fragmentation is useful if transactions on different sites tend to access different parts of the database. 18.6 Consider a relation that is fragmented horizontally by plant-number : employee (name, address, salary, plant-number) Assume each fragment has two replicas: one stored at the New York site and one stored locally at the plant site. Describe a good processing strategy for the following queries entered at the San Jose site. a. Find all employees at the Boca plant. b. Find the average salary of all employees. c. Find the highest-paid employee at each of the following sites: Toronto, Edmonton, Vancouver, Montreal. d. Find the lowest-paid employee in the company. Solution: a. i. Send the query ± name (employee) to the Boca plant. ii. Have the Boca location send back the answer. b. i. Compute the average at New York. ii. Send answer to San Jose.
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ECE456 Solution Sets A. Silberschatz, Database System Concepts , McGraw-Hill 18-2 c. i. Send the query to find the highest salaried employee to Toronto, Edmonton, Vancouver, and Montreal. ii. Compute the queries at those sites. iii. Return answers to San Jose. d. i. Send the query to find the lowest salaried employee to New York. ii. Compute the query at New York.
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This note was uploaded on 12/23/2009 for the course DBST 663 taught by Professor Tba during the Spring '09 term at MD University College.

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probs18 - ECE456 Solution Sets 18.2 Explain how the...

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