14. Describe the information the DBMS maintains in the system catalog. What are the generic names for three tables in the catalog and their corresponding names in Oracle? 15. The CUSTOMER table contains a foreign key, REP_NUM, that must match the primary key of the REP table. What type of update(s) to the CUSTOMER table would violate the foreign key constraint? 16. Which command do you use to obtain information from the system catalog in Oracle? 17. How is the system catalog updated? 18. What are integrity constraints? 19. How do you specify a general integrity constraint? 20. When would you usually specify primary key constraints? Can you specify them after cre- ating a table? How? 21. How do you specify a foreign key in Oracle