9-25. Suppose you created a file for each relation in your answer to Problem and Exercise 9-19. If the following queries represented the com- plete set of accesses to this database, suggest and justify what primary and secondary key indexes you would build.
a. For each PART, list all vendors and their associated prices for that part.
b. List all PART RECEIPTs, including related PART fields for all the parts received on a particular day.
c. For a particular VENDOR, list all the PARTs and their associated prices that VENDOR can supply.
9-26. Suppose that in a firm, employees have to undergo at least one training session of a communication course offered by the firm. Develop an E-R diagram for this situation. Identify primary keys for each entity and list some pertinent attributes. Also depict relations.
9-27. Convert the E-R diagram prepared for Prob- lem and Exercise 9-26 into relations. From Table 9-1, identify the rules that you utilized to achieve this.