Consider the global conceptual schema $C=C1|><msub><mrow><mi>|</mi></mrow><mrow><mn>0</mn></mrow></msub><mi>C</mi><mn>2</mn>$ of two local databases C $1$ and C $2.$ Optimize the

computation of the following expression:

${}_{\text{m}\text{i}\text{n}}(C1.$ Salary,$C2.$Salary

where $C1-C$ consists of tuples of C $1$ that have matching tuples in C $2,$ and C $2-$ C consists of tuples of C $2$

that have matching tuples in C$1.$