What is query processing? Explain its objectives in ddbms?
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Answer:
Objectives of Query Processing
Ø The main objectives of query processing in a distributed environment is to form a high level query on a distributed database, which is seen as a single database by the users, into an efficient execution strategy expressed in a low level language in local databases.
Ø An important point of query processing is query optimization. Because many execution strategies are correct transformations of the same high level query the one that optimizes (minimizes) resource consumption should be retained.
Ø The good measure of resource consumption are:
o The total cost that will be incurred in processing the query. It is the dome of all times incurred in processing the operations of the query at various sites and intrinsic communication.
o The resource time of the query. This is the time elapsed for executing the query. Since operations can be executed in parallel at different sited, the response time of a query may be significantly less than its cost.
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Answer:
The main objectives of query processing in a distributed environment is to form a high level query on a distributed database, which is seen as a single database by the users, into an efficient execution strategy expressed in a low level language in local databases.