question 23 3 pts the phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data—thus violating the isolation property of transactions. true false

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# Brief Explanations:
The described phenomenon is the "unrepeatable read" or a form of transaction isolation violation, but the specific scenario here (first transaction rolled back after second accessed uncommitted data) actually relates to the "dirty read" concept? Wait, no—wait, the question's description: when two transactions run concurrently, second accesses uncommitted data from first, then first rolls back. But the phenomenon of uncommitted data access (dirty read) is when a transaction reads data that another transaction has not yet committed. However, the statement's description: "the phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data—thus violating the isolation property of transactions." Wait, the key is: the definition of dirty read (uncommitted data read) is when a transaction reads data modified by another uncommitted transaction. If the first transaction is rolled back, the second transaction has read data that is now invalid (since first was rolled back), which is a dirty read, and it does violate isolation. But wait, the question is asking if the statement is True or False. Wait, the phenomenon of uncommitted data (dirty read) does occur in such a scenario: T2 reads T1's uncommitted data, then T1 rolls back. So the statement's description of the phenomenon is correct? Wait, no—wait, the phenomenon of uncommitted data (the problem's statement) is that when two transactions run concurrently, T2 accesses T1's uncommitted data, then T1 rolls back. So the phenomenon (dirty read) is when a transaction reads uncommitted data from another. So the statement is describing a scenario that is a dirty read (uncommitted data access), which is a violation of isolation. But wait, the question is: "The phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data—thus violating the isolation property of transactions." Wait, the term "uncommitted data phenomenon"—maybe the question is about the "dirty read" (also called uncommitted data read) which is a transaction isolation violation. So in this scenario, T2 reads T1's uncommitted data, then T1 rolls back. So the phenomenon (dirty read) does occur in this way, and it does violate isolation. Wait, but maybe I got it wrong. Wait, no—let's recall: Dirty Read: Transaction A modifies a row, Transaction B reads the modified row before A commits. If A then rolls back, B has read a row that never existed (in a committed sense). So the statement is describing a dirty read, which is a type of uncommitted data access, and it does violate isolation. So the statement is True? Wait, no—wait, the question's statement: "The phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data—thus violating the isolation property of transactions." So the phenomenon (uncommitted data, i.e., dirty read) is correctly described here: T2 accesses T1's uncommitted data, T1 rolls back. So the statement is correct, so the answer is True? Wait, no—wait, maybe I messed up. Wait, the phenomenon of uncommitted data (the problem's statement) is that the occurrence is when T2 accesses T1's uncommitted data, then T1 rolls back. So the statement is saying that this scenario is when the phenomenon of uncommitted data (dirty read) occurs. So the statement is correct, so the answer is True? Wait, but let's check again. The isolation property (like in ACID) requires that transactions are isolated, so dirty reads violate isolation. So the scenario described is a dirty read (uncommitted data read), which is a violation of isolation. So the statement is correct, so the answer is True? Wait, no—wait, maybe the question is a trick. Wait, the phenomenon of uncommitted data (the term) is the dirty read. So the statement is describing the scenario where dirty read happens, so the statement is True. Wait, but I'm confused. Let me re-express: The statement says: "The phenomenon of uncommitted data occurs when two transactions are executed concurrently and the first transaction is rolled back after the second transaction has already accessed the uncommitted data—thus violating the isolation property of transactions." So:

- Phenomenon: uncommitted data (dirty read) occurs in this scenario.

- Is this correct? Yes, because dirty read is when a transaction reads data from another uncommitted transaction. If the first is rolled back, the second has read data that is now invalid (since first was rolled back), which is a dirty read and violates isolation. So the statement is correct, so the answer is True? Wait, but maybe the answer is False? Wait, no—wait, maybe I got the phenomenon wrong. Wait, the "uncommitted data" phenomenon (dirty read) is when a transaction reads uncommitted data. The scenario here is T2 reads T1's uncommitted data, then T1 rolls back. So the phenomenon (dirty read) does occur in this way. So the statement is correct, so the answer is True.
# Answer:
True

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