Consider concurrent execution of two transactions $T1$ and $T2$ in a DBMS, both of which access a data object $A$. For these two transactions to not conflict on $A$, which one of the following statements must be true?

Two operations on the same data item by different concurrent transactions are in conflict if and only if at least one of the operations is a write operation (i.e., read-write, write-read, or write-write).

Therefore, for transactions $T1$ and $T2$ to not conflict on data object $A$, neither transaction can perform a write operation on $A$. Both transactions must only read $A$.

• (A) Both $T1$ and $T2$ only read $A$ (Read-Read): Non-conflicting. Correct.

• (B) $T1$ reads $A$ and $T2$ writes $A$ (Read-Write conflict): Conflicting.

• (C) $T1$ writes $A$ and $T2$ reads $A$ (Write-Read conflict): Conflicting.

• (D) Both $T1$ and $T2$ write $A$ (Write-Write conflict): Conflicting.