This a question of Advances Database please help me

a) Given the table Products (ProductID, ProductName, CategoryID, UnitPrice), please write code to declare a stored procedure listing all products cheaper than the average price of their corresponding CategoryID. (2pts) b) What is Trigger? Give and explain 3 examples in which Trigger is useful. (4 pts) c) What is the lost update problem in a multi-user DB environment? Given an example when this problem occurs (2 pts). d) (3pts) Draw a precedence graph for below execution plan of 3 transactions (1,2,3) with 2 resources (X and Y). Note: r stands for "read" while w stands for "write". r2(x), r1(Y), w2(X), r3(X), w1(Y), w3(X), r2[Y), w2[Y) Is this execution serializable? e) (5pts) According to the Data warehouse definition of W.H. Inmon, what are characteristics of a datawarehouse? Explain one of them