Consider a database with objects x and y and assume that there are two transactions t1 and t2. transaction t1 reads objects x and y and then writes object x. transaction t2 reads objects x and y and then writes objects x and y. give three example histories over transactions t1 and t2 that result in :

a)a write-read conflict

b)a read-write conflict

c)a write-write conflict

show that each serial history involving transactions t1 and t2 preserves the consistency requirement of the database.

specify a recovery strategy which would never require undoing or re-doing side-effects (both undoing and redoing are not required).

how would such a recovery strategy be implemented?

Write a program that displays the following menu: geometry calculator 1. calculate the area of a circle 2. calculate the area of a rectangle 3. calculate the area of a triangle 4. quit enter your choice (1-4): if the user enters 1, the program should ask for the radius of the circle and then display its area. use the following formula: area = ď€(the square of r) use 3.14159 for ď€ and the radius of the circle for r. if the user enters 2, the program should ask for the length and width of the rectangle and then display the rectangle’s area. use the following formula: area = length * width if the user enters 3, the program should ask for the length of the triangle’s base and its height, and then display its area. use the following formula: area = base * height * .5 if the user enters 4, the program should end. input validation: display an error message if the user enters a number outside the range of 1 through 4 when selecting an item from the menu. do not accept negative values for the circle’s radius, the rectangle’s length or width, or the triangle’s base or height. note: if the user enters an improper menu choice (1-4), the program prints "the valid choices are 1 through 4. run the program again and select one of those." if the user enters a negative radius, the program prints "the radius can not be less than zero." if the user enters a negative value for height or base, the program prints "only enter positive values for base and height."