In what type of topology is each site connected to two other sites, ?providing redundancy?

Given the expression a + b. What type of expression is this?

a. prefix b. postfix c. outfix d. infix

Consider the three transactions T1, T2, and T3, and the schedules S1 and S2 given below. Draw the serializibility (precedence) graphs for S1 and S2 and state whether each schedule is serializable or not. If a schedule is serializable, write down the equivalent serial schedule(s).

T1: r1(x); r1(z); w1(x) T2: r2(z); r2(y); w2(z); w2(y) T3: r3(x); r3(y); w3(y) S1: r1(x); r2(z); r1(x); r3(x); r3(y); w1(x); w3(y); r2(y); w2(z); w2(y) S2: r1(x); r2(z); r3(x); r1(z); r2(y); r3(y); w1(x); w2(z); w3(y); w2(y)