Locks placed by command are implicit locks.
Answer: B
Correct answer: False
Locks placed by command are explicit; implicit locks are those the DBMS places on its own initiative to enforce the isolation level in force. The two terms classify locks by who asked for them, which is a different question from whether the lock is shared or exclusive.
Please log in or register to report this question.
The goal of database security is to ensure that only authorized users can perform authorized activities at authorized times.
Answer: A
Correct answer: True
All three qualifications are needed. Authorised users, so that identity is established; authorised activities, so that a user may read what they may not change; and authorised times, since access appropriate during a shift may not be appropriate outside it. Authentication establishes the first and authorisation the other two.
Please log in or register to report this question.
A phantom read occurs when a transaction rereads data it has previously read and finds modifications or deletions caused by a committed transaction.
Answer: B
Correct answer: False
What is described is a nonrepeatable read: rows already seen have been modified or deleted by a committed transaction. A phantom read is the appearance of new rows that were not there before. The distinction decides which isolation level is needed, since repeatable read prevents the first but not the second.
Please log in or register to report this question.
A transaction is a series of actions to be taken on the database so that either all of them are performed successfully or none of them are performed at all.
Answer: A
Correct answer: True
This is the definition of a transaction and it is the atomicity property stated in full. The series of actions is treated as a single indivisible unit, so a transfer between two accounts either debits one and credits the other or does neither - the database is never left with the money in neither place.
Please log in or register to report this question.
A point of synchronization between the database and the transaction log is generally referred to as a stop point.
Answer: B
Correct answer: False
A point of synchronisation between the database and its log is a checkpoint. At a checkpoint the buffers are written out and the log records the fact, so recovery need only go back to the last checkpoint rather than to the beginning of the log - which is what keeps recovery time bounded.
Please log in or register to report this question.
An exclusive lock locks the item from change but not from read.
Answer: B
Correct answer: False
That describes a shared lock, which permits others to read but not to change. An exclusive lock excludes access of every kind, reading included, which is what a writing transaction requires. Several shared locks may be held on one item at once; an exclusive lock may not coexist with any other.
Please log in or register to report this question.
Money is defined in Oracle with the Currency data type.
Answer: B
Correct answer: False
Oracle has no Currency datatype. Money is held in a NUMBER column with an explicit precision and scale, such as NUMBER(9,2), which stores the value exactly rather than in binary floating point - and exactness is what matters for money. The Currency type belongs to other products.
Please log in or register to report this question.
