Database Management System

Q201.

Amongst the ACID properties of a transaction, the 'Durability' property requires that the changes made to the database by a successful transaction persist
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Q202.

Consider the following schedules involving two transactions. Which one of the following statements is TRUE? S_1 :r_1(X); r_1(Y); r_2(X); r_2(Y); w_2(Y); w_1(X) S_2 :r_1(X); r_2(X); r_2(Y); w_2(Y); r_1(Y); w_1(X)
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Q203.

Consider the following two transactions : T1 and T2. T1:read (A); read (B); if A = 0 then B \leftarrow B + 1; write (B); T2 : read (B); read (A); if B \neq 0 then A \leftarrow A - 1; write (A); Which of the following schemes, using shared and exclusive locks, satisfy the requirements for strict two phase locking for the above transactions?
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Q204.

Consider the following schedule S of transactions T1 and T2:{\begin{array}{l|l} \textbf{T1}& \textbf{T2} \\\hline \text{Read(A)} \\ \text{A = A ? 10}\\ & \text{Read(A) }\\ & \text{Temp = 0.2*A} \\ & \text{Write(A)} \\ & \text{Read(B)} \\ \text{Write(A)}\\ \text{Read(B)}\\ \text{B = B + 10}\\ \text{Write(B)} \\ & \text{B = B + Temp} \\ & \text{Write(B)}\\ \end{array}}Which of the following is TRUE about the schedule S ?
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Q205.

Consider the following schema:Emp (Empcode, Name, Sex, Salary, Deptt)A simple SQL query is executed as follows: SELECT Deptt FROM Emp GROUP by Dept Having avg (Salary) > {select avg (Salary) from Emp}The output will be
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Q206.

Which of the following scenarios may lead to an irrecoverable error in a database system?
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Q207.

For the schedule given below, which of the following is correct:\begin{array}{lll} \text{1} & \text{Read A} & \text{} \\ \text{2} & \text{} & \text{Read B} \\ \text{3} & \text{Write A} & \text{} \\ \text{4} & \text{} & \text{Read A} \\ \text{5} & \text{} & \text{Write A} \\ \text{6} & \text{} & \text{Write B} \\ \text{7} & \text{Read B} & \text{} \\ \text{8} & \text{Write B} & \text{} \\\end{array}
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Q208.

Consider three data items D1,D2 and D3 and the following execution schedule of transactions T1,T2 and T3. In the diagram, R(D) and W(D) denote the actions reading and writing the data item D respectively. Which of the following statements is correct?
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Q209.

Let R and S be relational schemes such that R={a,b,c} and S={c}. Now consider the following queries on the database: I.\pi _{R-S}(r)-\pi_{R-S}(\pi_{R-S}(r) \times S -\pi_{R-S,S}(r)) II.\{t|t\in \pi _{R-S}(r)\wedge \forall u \in s (\exists v \in r(u=v[s]\wedge t=v[R-S]))\} III.\{t|t\in \pi _{R-S}(r)\wedge \forall v\in r(\exists u\in s(u=v[s]\wedge t=v[R-S]))\} IV. Select R.a, R.b From R,S Where R.c=S.c Which of the above queries are equivalent?
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Q210.

Consider the relation employee(name, sex, supervisorName) with name as the key. supervisorName gives the name of the supervisor of the employee under consideration. What does the following Tuple Relational Calculus query produce?
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