1. 1 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Views and Security 3

2. 2 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Outline views generalities updating through views security

3. 3 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College 1

4. 4 General Definition a view is a perspective of the database different users may need to see the database differently; this is achieved through the view mechanism a view is part of the external level remember the three level architecture: internal, conceptual and external

5. 5 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College View - a window to the database the database - a set of base tables

6. 6 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College View named relational expression virtual relation substitution process

7. 7 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College View in SQL named SELECT statement some restrictions apply (not any SELECT statement can be declared as a view) CREATE VIEW [ ] AS [WITH CHECK OPTION] ; DROP VIEW ; ::= RESTRICT | CASCADE

8. 8 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College SQL views - examples consider Employee ( Emp_Id, Name, Address, Salary, Dept_id ) Department (Dept_id, Manager, Budget, Office ) CREATE VIEW Emp AS SELECT Emp_Id, Name, Address, Dept_id FROM Employee ; CREATE VIEW GoodEmp AS SELECT Emp_id, Name, Address, Salary, Dept_id FROM Employee WHERE Salary > 45 ;

9. 9 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College SQL views - examples consider Employee ( Emp_Id, Name, Address, Salary, Dept_id ) Department (Dept_id, Manager, Budget, Office ) CREATE VIEW SafeEmployees AS SELECTName, Employee.Dept_id FROM Employee, Department WHERE Budget > 1500 AND Employee.Dept_id = Department.Dept_id

10. 10 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College SQL views - examples consider Employee ( Emp_Id, Name, Address, Salary, Dept_id ) Department (Dept_id, Manager, Budget, Office ) CREATE VIEW TotSalPerDept AS SELECTDept_id, SUM(Salary) AS TotSal FROMEmployee GROUP BYDept_id

11. 11 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College SQL Views - use views are used as if they were base relations from the point of view of the user, a view is the same as a base relation however, certain restrictions exist in a view, a column that is based on an aggregate function cannot be subject to an aggregate function or to a WHERE clause (e.g. TotSal before) a grouped (contains GROUP BY) view may never be joined with a base table or another view

12. 12 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College With Check Option only for updateable views migrating rows a row of a view, after being updated, may not satisfy the condition of the view anymore, therefore it will migrate out of the view WITH CHECK OPTION avoids such situations; the update is not permitted if the row will no longer satisfy the condition of the defining query

13. 13 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Advantages automatic/improved security reduced complexity through macro facility customisation the same data can be seen differently by users through macro facility data integrity –WITH CHECK OPTION

14. 14 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Disadvantages update restriction will see in more detail next lecture structure restriction performance

15. 15 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College 2

16. 16 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Data manipulation operations on views retrieval operations in theory in practice (SQL92) update operations in theory - basics in practice (SQL92)

17. 17 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Application suppose Student ( S_id, Name, Address, Programme, Tutor, …) Tutor ( T_id, Name, Address, …) Course ( C_id, Name, Length, …) C_Reg ( S_id, C_id,... ) suppose all tutors need access to all course-lists, but are not allowed to see other information about students; this can be expressed as a view

18. 18 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College View Course Lists CREATE VIEW Course-lists (Student, Tutor, Course) AS SELECT (Student.Name, Tutor.Name, Course.Name) FROM Student, Tutor, Course, C_Reg WHERE Tutor = T_id AND Course.C_id = C_Reg.C_id AND Student.S_id = C_Reg.S_id ;

19. 19 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Data operations on Course Lists retrieve delete update insert ANY OPERATION ON A VIEW HAS TO BE PROPAGATED TO THE BASE RELATIONS on which the view is defined

20. 20 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Retrieving from Course Lists -- all students that take Database Systems SELECT Student FROM Course-lists WHERE Course = Database Systems ; --Marians tutees and the courses they take SELECT Student, Course FROM Course-lists WHERE Tutor = Marian ; --etc.

21. 21 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Insert into Course List insert the fact that Bob Marley, whos personal tutor is Marian Ursu, has registered for Database Systems INSERT INTO Course-lists VALUES (Bob Marley, Marian Ursu, Database Systems); how should this work? why?

22. 22 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Deleting a student from a Course Lists

23. 23 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Principle a view should look like and behave exactly like a base relation satisfied, in theory, in case of retrieval operations in practice, even in case of retrieval operations, it is sometimes violated; e.g. in SQL92 (recall restrictions – see p. 11):

24. 24 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College SQL rules for updating views the FROM clause of the SELECT statement of the defining query contains exactly one table reference (the view is defined on exactly one table), i.e. the view definition does not contain JOIN, UNION, INTERSECT or EXCEPT every element in the SELECT statement of the defining query is a column name (rather than a calculated field, aggregate function, …) the SELECT clause defining the view does not contain the word DISTINCT the defining query does not include a GROUP BY clause etc … (refer to the text book)

25. 25 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College 3

26. 26 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College The problem of data security aspects origins of security rules social - legal, ethical, political, strategic,... operational problems are the computers safe? does the operating system have a security system (passwords, storage protection keys...)?... does the DBMS have a concept of data ownership?

27. 27 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College SQLs GRANT and REVOKE GRANT ON TO | PUBLIC [ WITH GRANT OPTION ] REVOKE [ GRANT OPTION FOR] ON FROM

28. 28 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Clarifications privileges USAGE (for domains), SELECT, INSERT (column specific), UPDATE (column specific), DELETE, REFERENCES (for integrity constraint definitions) DOMAIN [ TABLE ] (a base table or a view) RESTRICT | CASCADE

29. 29 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Example #1 CREATE VIEW View1 AS SELECT S_id, S_name, Status, City FROM SuppliersWHERE City = Paris GRANT SELECT, INSERT, UPDATE ( S_name, Status ), DELETE ON View1 TO Mark, Spencer

30. 30 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Example #2 CREATE VIEW View2 AS SELECT S_id, S_name, Status, City FROM S WHERE EXISTS ( SELECT * FROM SP WHERE EXISTS (SELECT * FROM P WHERE S.S_id = SP.S_id AND P.P_id = SP.P_id AND P.City = Rome )) ; GRANT SELECT ON View2 TO John

31. 31 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Example #3 CREATE VIEW View3 AS SELECT P_id, ( SELECT SUM (Contracts.Qty) FROM Contracts WHERE Contracts.P_id = Parts.P_id ) AS Quantity FROM Parts; GRANT SELECT ON View3 TO Bill

32. 32 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Context dependent/independent rules context-independent rules the previous examples context-dependent rules the rule and/or the view definition will contain context dependent functions date(), day(), time(), terminal()

33. 33 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Example #4 GRANT INSERT ON Transactions WHERE Day() NOT IN (Saturday, Sunday) AND Time() > 9:00 AND Time() < 17:00 TO Till; --Till is a group of users

34. 34 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Other issues logical OR between security rules anything not explicitly allowed is implicitly prohibited

35. 35 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College –

36. 36 Term 2, 2004, Lecture 6, Views and SecurityMarian Ursu, Department of Computing, Goldsmiths College Conclusions views generalities updating through views security