The cost of reading and writing temporary files while evaluating a query can be reduced by
Answer: B
Correct answer: pipelining
Without pipelining each operation writes its whole result to a temporary file for the next to read. Pipelining passes each tuple straight from one operation to the next as it is produced, so the intermediate results are never written to disk at all.
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A transaction is in the ______ state after its final statement has been executed and its changes have been written to the database.
Answer: C
Correct answer: committed
A transaction becomes partially committed when its last statement has executed but its changes are not yet certain to survive; it becomes committed once they have been written durably. The distinction is what makes recovery possible.
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In multiple granularity of locks SIX lock is compatible with
Answer: B
Correct answer: IS
A SIX lock - shared with intention exclusive - means the holder is reading the whole subtree and intends to write part of it. Another transaction may still hold an IS lock, since reading is compatible with reading; but IX, S and SIX all conflict, because each would either write where SIX reads or read where SIX intends to write.
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The statement that is executed automatically by the system as a side effect of the modification of the database is
Answer: D
Correct answer: trigger
A trigger is a piece of code the DBMS runs automatically when a specified modification occurs, which is exactly the description given. An assertion is a condition that must hold but does not itself act.
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The normal form that is not necessarily dependency preserving is
Answer: A
Correct answer: BCNF
A relation can always be decomposed into third normal form while preserving all its functional dependencies, but a BCNF decomposition sometimes cannot: enforcing one of the original dependencies may require a join. That is the price of BCNF's stronger guarantee, and it is why 3NF is often preferred in practice.
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The normalization was first proposed by .
Answer: B
Correct answer: Codd
E. F. Codd proposed normalisation along with the relational model. Note the spelling of the name and that Boyce-Codd normal form, named jointly, came later.
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The division operator divides a dividend A of degree m+n by a divisor relation B of degree n and produces a result of degree
Answer: D
Correct answer: m
Division cancels the divisor's attributes: dividing a relation of degree \( m+n \) by one of degree \( n \) leaves a result of degree m. The result contains those values of the remaining m attributes that appear with every tuple of the divisor.
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Which of the following is not a characteristic of a relational database model?
Answer: B
Correct answer: Tree like structure
A relational database is a set of independent tables with no structural links between them; relationships are expressed by matching values, not by pointers. The tree is the hierarchical model's structure.
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Assume transaction A holds a shared lock R. If transaction B also requests for a shared lock on R.
Answer: C
Correct answer: It will immediately be granted.
Shared locks are compatible with one another, since reading does not interfere with reading. B would have to wait only if A held an exclusive lock or if B were asking for one.
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In E-R Diagram total participation is represented by
Answer: A
Correct answer: Double lines
Double lines joining an entity to a relationship indicate total participation - every entity in the set must take part. A single line indicates partial participation.
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