Databases:

1
???? ???????????

• Databases
• An Introduction

2
????? ??????? ?????? ????? ?????? ???? ??????

• ?? ??? ???????? ?????????

3
??? ??? ???????

• ??? ?????? ??? ???? ?? ?????? ?????? ????? ???
  ????? ??????? ????? ?????? ???? ??????, ????????
• Database Management System (DBMS)
• ???? ????? ??? ????? ??? ??? ?? ???? ???? ?????
  ????? ??????
• ???? ????? ???? ???? ????????

4
??? ????????

• ?????? ?????? ???? ???? ???? ??????? ??????
  ????????
• ??? ?????? ?????? ????? ??????? ??????? ??????
  ??????? ?????? ??????? ???? ?????? ???? ??????
  ????? ??????? ?? ??????
• ?? ?? ????? ??????? ?????? ?????? ?-PC ????
  ?????????? ?? ???? ??????, ???? ????? ??????
  (????, spreadsheets)

5
???????

• ?.?.?., ????? ????? ?????? ???????, ????? ????
  ??????? ???????
• ??????? ??????? ??? (????? ?????, ????? ???') ???
  ?????? ???? ??????? ????? ????? ???? ?????? ????
  ????? ?????? ????? ?????, ????? ?????? ?.?.?.
  ?????? ????? ??????

6
??? ?? ?????

• ???? ???? ??? ???? ????? (????? ????? ???????)
  ??? ???? ??????, ???? ????? ?? ???? ?????
• ????? ????? ???? ???? ?????? ?????? ??? ?????
  ????? ?? ??????? ?????? ??????? ????? ?? ?.?.?.
  (?? ?? ??? ????? ???? ?? ??????? ????? ?????? ?"?
  ??????)

7
?? ???? DBMS?
8
?????? ??????
DBMS ???? ?? ??? ????? ?????? ?????? ??????? ??
???? ???? ?????? ?????
??? ?????? ???? ?????? ???? ???? ???? ????? ????
??? ?????? ????
?? ?????? ????? ?????? ???? ??? ??????, ???
??????? ?????? ???? (?? ?????) ?? ???? ????????
????? ????
9
??? DBMS?????? ?????? ???? ??????

• ????? ????? ?????? ???? ???? ?????? ????? (??????
  ?????????), ???????
• ?????? ????? ??? ?? ????? ?? ???????
• ???? ???? ??? ?????? ???????? ?? ?? ???????
• ???? ???? ??? ??????? ???????? ???????
• ????? ?????? ????? ?"? ??? ???????
• ??? ??, ?????? ???? ?????? ?????? ??????

10
??? DBMS? (????)???? ?????? ???????

• ???? ?????? ??-????? (??????)
• ????? ?????? ????? ?"? ???? ????? ????? ????
• ???? ????? ????????? (backup recovery)
• ?????? ????? ?????? ????? ?? ?????
• ????? ?? ????? ??????? (data integrity)
• ?????? ????? ???????, ????
• ?? ???? ???? ??? ?????? ?????
• ??? ???? ??? ???? ??? ???
• ???? ??? ???? ???? ??? 0 ?- 100
• ????? ?? ?????? ??????? (security) ?"? ??? ??????
  ??????? (authorization)

11
?????? ??????

• ???? ???????
• ???? ?????
• ???? ?????
• ???? ?????

12
???? ???????

• ???? ??????? ??? ???? ?? ?????? ???????? ??? ????
  ????? ?????? ?? ??????? ??? ??????? (???,
  ???????? ?? ???????)
• ??????? ??? ???? ??????? ???? ??????? ????
• ???? ????? ?? ???? ???????
• ????? ?????? ??? ????? ????? ??????
• ???? ??????? ?????? ????? ??????
• ????? ????? ????? ??? ????? ????? (????? ????????
  ?? Relational Model)

13
???? ?????

• ????? ?????? ????? ?? ?????? ????? ?? ???????
• ???? ???????
• ????? ??????? ?? ?????
• ????????
• ????, ?????? (?? ????? ?? ????? (hashing)) ??
  ???? ?????, ?????? ????? ??????? ????? ?? ??????
  ??? ???? ?????

14
???? ?????

• ????? ?????? ????? ?? ???????? (???, ??????
  ???????) ?? ?????? ?????, ?? ??????? ??????,
  ??????
• ??????? ?????? ????????, ?????, ??????, ?????
  ???'
• ?????? ????? ????? ????, ????? ???'
• ?? ??? ??? ?????? ???? ??????? ???
• ?? ??? ??? ?????? ???? ?????? ???

15
???? ?????Levels of Abstraction

• ????? ????? ???? ???? ?? ?????
• ???? ????? (Physical Schema)
• ???? ?????? (Conceptual Schema)
• ???? ???? ????? ?? ?? ???????
• ????? (Views)
• ??? ????? ??????, ??? ??? ??? ?????? ??? ????????
  ?????? ???? ????????? ???????

16
Levels of Abstraction

• ?? ??? (View) ???? ???? ????? ??????? ?????? ????
  ?? ???????
• ?????, ?? ???????? (??????) ????? ???? ???? ?????
  ??? ???? ????? ???????

View 1
View 2
View 3
Conceptual Schema
Physical Schema
??????, ???????? ??????? ?????? ?????? ?? ??????
???? ??? ??? ????? ?? ?? ??????? ?? ????????
??????? ????? ???? ?? ????? ???? ?? ?????
???????????

• .

17
???? ??? ???? ??????

• ????? ?????? ?????? ??????? ??????? ????? ???
  ??????, ??????
• Data Definition Language (DDL)
• ?????? ??????? ?- SQL (????? ?????)
• ??????? ?? ????? ?????? ?????? ????? ?? ?? ??????
  ?? ?? ??? ???? ???????

18
???? ???? ???? ???? ????? ?

• ????? ?? ???? ???? ????? ????? ????? ?? ?? ????
  ??????? (Data Independence)
• ?? ???? ??????? ?????? ???????? ???????? ???? ???
  ?? ??????? ?? ???? ?????? ?? ?????? (????? ??????
  ???? ?? ?????? ??? ?????)
• ??????, ????? ?????? (????? ????? ????? ??
  ??????) ???? ?????? ????? ???? ???????

19
?????? ????? ?????? ???? ?????? ?????

• ???? ?????? ????? ???? ???? ?????
• ??? ??????? ????? ?????? ?????? ?????? ??????
• ?????? ???? ?????? ("?????") ??-?????
• ????? ????????? (backup recovery)
• ????? ??????? (data integrity)
• ????? ???? (data security) ???????
  (authorization)
• ??? ?????? ?? ?????? (views) ?????? ???? ??????

20
????? ????? ??????

• The Relational Model Briefly

21
??? ??? ????? ????

• ??? ????? ?????? ?????
• ??? ?????? ????? ????? ??????
• ??????, ????? ???? ????? ?????? ???? ???? ??????,
  ?? ?????? ???? ???????? ?? ???????

???? ????? ????? ?????
year sname sid
3 white 240
3 jones 202
1 adams 450
?? ?? ????? ???? ????????
22
???? ?????? (?????)

• ????? ??? ????? n-?? ?? ?????
• ????????? ??? n-??? ????? ?? ??? ????? ?? ?? ???
  ?????? ????, ??????
• (240,white,3) ? (white,240,3)
• ??? ?????? ?? ???? ??????? ???? ??????? ?????
  ???? ?? ???

year sname sid
3 white 240
year sid sname
3 240 white

23
???? ???? (???, ???? ?????) ????? ??????

• ??????????? (???, ???????) ??????? ?? ????? ?????
  ?? ?????, ????? ???? (?? ????? ?????? ??????)
• ??????? ??? ????? ??' ??????, ?? ?????? ????
  ???????? ?? ???????
• ??????? ?????? ?????? ??????? ?? ????
• ?????? ????? ????????
• ?????? ?????? ?????? ?? ????????

24
????? ?????? ?? ??? ????? ???????

• ????? ?????? ?? ??? ??? ????? ??????????? (????
  ???????) ?? ????
• ????? ?????? ?? ???? ????? ???
• sid, sname, year
• ???? ??? ?????, ?? ???? ??
  ??????? ???? ???? ???? ???
  ?????? ?? ???? ??

year sname sid
3 white 240
3 jones 202
1 adams 450
25
????? ???? ????? ?????? ?? ??? ????? ????? ??????

• ?????? ???????? ?? ???? ????? ????? ????? ????
  ????? ???? ??? ?????? ??????? ?????????
• ????? ???? (???, ????????? ???? ????? ?? ???
  ?????? ?????? ???? ??????), ????? ?????? ?? ???
  ????? ????? ??????, ????
• ?- type ?? ?? ????????
• ?? ???? (????? ?? ?? ??? ????? ????? ?? ????
  ??????????)
• ??????? ????? ?????

26
??? ????? ?????? ?? ????

• ????? ?????? ?? ??? ????? ????? ???? ???? ???????
  (data structure) ?? ????
• ??????, ???? ?????? ????? ???? B-tree, ????
  ????? ??? ????? ??? ??? ???? ??????
• ?????? ???? ??? ????? ?????? ????? ?????
  (hashing)
• ????? ?????? ????? ?? ????? ??????
• ????, ?? ?????? ?? ?? ??????, ?????? ?????
  ??????? ????? ??? ?? ???????

27
???? ?????? ?????

• An Introduction to Schema Design

28
???? ????? ??? ?????? ???, ????

• ????? ?? ????? ??????
• ????? ??? ?? ????? ?????? ????? ????? ????? ?????
  ????? ?? ?? ??????? ????????? ????? ????? ???????
  ??????????
• ????? ?? ????? ??????
• ????? ??? ?? ????? ?????? ????? ???????
  ?????????? ?? ??????? ??????????
• ????? ??????? ?????????? ????? ?????? (????, ????
  ???? ??????)

29
???? ????? ???? ?????

• ????? ???? ??? ?????? ???????, ????? ??????
  ?????? ?????? ??? ?????? (?? ?????? ??????
  ??????)
• ?????, ?????? ????? ?????? ?????? ?????? ?? ?????
  ????? ????
• ?????? ?????? ?? "????" ??? ???? ????? ?? "?????"
  ?? "?????" ?????? ??? ????? ?????? (???????
  ??????? ?????? ?? ?????)
• ?????? ????? ????? ????? ??????

30
????? ????? ?????? ?????

• ????? ???? ?????? ???? ?? ????? ???? ???? ??????
  ?????? (?? ?? ???? ?????)
• ???? ???? ??? ????? ????? ???? ????? ???? ????
  ???? (?????? ???????) ?????? ????? ???? ?? ?????
  ???? ?? ????? ?????
• ?? ?????? ????? ?????, ???? ?? ????? ?? ?????
  ???????? ?????? ??????? ????? (??????, ????
  ?????? ????? ?????)

31
????? ?????? ????? (??? ?? ?????) ????? ????
?????? ?????? ????? ?????

• ????? ??????? ???? ?? ???? ?? ????? ????? ??????
  ?????? ?????
• ??????, "????? ????????????" ????
• ????????
• ?????
• ??????
• ???? ?????
• ????? ????
• ?????? ????
• ????...

32
???? ??????? ???????

• The Entity-Relationship Model

33
???? ????? ???????Entity-Relationship Model

• ???? ??????? ??????? ??? ???? ?????? ?????? ?????
  ?????, ?????? ????? ???? ???????
• ???? ??????? ??????? ???? ????? ?????? ??????
  ????? ????? ?? ??????? ?????
• ???? ????????
• ????? ?????? ????? ?????? ?????

34
?????

• ???? ?????? ????? ???? ????, ????? UML
  (Universal Modeling Language)
• ???? ????? ??????? ????? ??????? ??????? ?????
  ?????? ????? ????? ?? ??????? ?????, ???? ????
  ?????? ????? ?????
• ????? ????? ????? ???? ????? ?? ???????
  (classes) ??? ?????????? ?????
• ISA Hierarchy (Inheritance Hierarchy)
• Aggregation (or Composition) Hierarchy

35
??? ???? ?? ???? ??????? ???????

• ????? ????? ??????? ??????? ??? ???????
• ????? ???????
• - ???????? - ??????
• - ????? - ???? ?????
• ????? ??????
• - ??? ??? ?????? ?????????
• - ??? ??? ?????? ??????
• - ??? ??? ?????? ????? ?????

36
??????

• Entities

37
???? ?????? ??????Entity and Entity Set

• ???? ??? ??? ????? ????? ???? ?? ??????
• ??????, ?????? ??? ???? ???? ???????
• ??, ?????, ????? ????, ?? ???, ???? ???? ???'
• ?? ???? ????? ?????? ????? ??? ????? ?????? ?????
  ???? ????? ?? ?????? ???????, ??????
• ?????? ????? (???? ?????) ?"? ??, ????? ???? ???
  ???
• ???? ????? ?????? ?"? ??' ???? (?? ??' ??????)
• ?? ??????? ????? ??? ?????? ?????? ?????? ???
• ??????, ????? ??????? ?? ?????????

38
???? ?????? ??????Entity and Entity Set
??? ??? ??????? ??? ????? ?? ?????? ?? ???? ????
?????

• ???? ??? ??? ????? ????? ???? ?? ??????
• ??????, ?????? ??? ???? ???? ???????
• ??, ?????, ????? ????, ?? ???, ???? ???? ???'
• ?? ???? ????? ?????? ????? ??? ????? ?????? ?????
  ???? ????? ?? ?????? ???????, ??????
• ?????? ????? (???? ?????) ?"? ??, ????? ???? ???
  ???
• ???? ????? ?????? ?"? ??' ???? (?? ??' ??????)
• ?? ??????? ????? ??? ?????? ?????? ?????? ???
• ??????, ????? ??????? ?? ?????????

39
????? ?????? ?"? ??????

• ???? ????? ???? ?"? ?????, ??????
• ???? ??????
• ?? "???? ???"
• ????? "????? ???? 107 ???????"
• ????? ???? "7.8.78"
• ?? ??? "????"
• ???? ???? "1673040"
• ????? (???? ???, ????? ???? 107 ???????, 7.8.78,
  ????, 1673040)

40
????? ?????? ?"? ??????
????? ?? ??????? ????? ???? ??? ????? ???

• ???? ????? ???? ?"? ?????, ??????
• ???? ??????
• ?? "???? ???"
• ????? "????? ???? 107 ???????"
• ????? ???? "7.8.78"
• ?? ??? "????"
• ???? ???? "1673040"
• ????? (???? ???, ????? ???? 107 ???????, 7.8.78,
  ????, 1673040)

41
???? (Key) ?? ????

• ????? ?? ????? ?????? ????? ???? ????? ??? ?????
  ????? ???? (Key)
• ??????, ??' ?????? ??? ???? ?? ??????
• ???? ???? ??? ???? ?? ????, ??? ?? ?? ???? ????
  ????, ?? ?????? ????? ??? ?????? ????? (???????
  ?????) ?? ???? ??

42
?????

• Relationships

43
??? ?????? ?????Relationship Relationship Set

• ??? ???? ????? ?? ?????? ???? ??????? ???, ??????
• ??????? "??? ???" ???? ?? ????? "?????? ?????"
  ????? ????? "????? ???"
• ??? ??? ?????, ??? ??? ???? ??????
• ????? ?????? ????????
• ??????? "??? ???" ???? ?? ????? "?????? ?????"
• ????? "????? ???" ???? ?? ????? "?????? ?????"
• ?? ?????? ????? ??? ?????? ?????? ???

44
??? ?????? ?????Relationship Relationship Set
?? ????? ???? ????? ???? ????? ????? ??? ?????
??? ?? ??? ????? ????????? ???? ???? ?? ?? ?????
???????

• ??? ???? ????? ?? ?????? ???? ??????? ???, ??????
• ??????? "??? ???" ???? ?? ????? "?????? ?????"
  ????? ????? "????? ???"
• ??? ??? ?????, ??? ??? ???? ??????
• ????? ?????? ????????
• ??????? "??? ???" ???? ?? ????? "?????? ?????"
• ????? "????? ???" ???? ?? ????? "?????? ?????"
• ?? ?????? ????? ??? ?????? ?????? ???

45
????? ????? ?"? ??????

• ???? ????? ??? ?"? ?????, ??????
• ???? ??????? "??? ???" ???? ?? ????? "??????
  ?????" ????? ????? "????? ???"
• ?????? (??? ???, ?????? ?????, ????? ???)
• ???? ??????? "??? ???" ???? ?? ????? "??????
  ?????"
• ?????? (??? ???, ?????? ?????)
• ???? ????? "????? ???" ???? ?? ????? "??????
  ?????"
• ?????? (????? ???, ?????? ?????)

46
????? ????? ?"? ??????
????? ?? ?????? ????? ???? ??? ????? ???

• ???? ????? ??? ?"? ?????, ??????
• ???? ??????? "??? ???" ???? ?? ????? "??????
  ?????" ????? ????? "????? ???"
• ?????? (??? ???, ?????? ?????, ????? ???)
• ???? ??????? "??? ???" ???? ?? ????? "??????
  ?????"
• ?????? (??? ???, ?????? ?????)
• ???? ????? "????? ???" ???? ?? ????? "??????
  ?????"
• ?????? (????? ???, ?????? ?????)

47
?????? ??????

• Additional Points

48
???? ????? ??????? ??????? ????? ?????

• ??? ?????? ???? ????? ?? ????? ?????? ??? ?????
  ????? ?"? ??? ?????
• ????? ?????? ?? ????? ?????? ??????

49
???? ???? ?????

• ????? ?? ???? ????? ????????
• ????? ?? ??? ????? ????????
• ?? ??? ????? ????? ????? (Attribute) ???? ???
  ?????? ??? ?????? ?????, ??? ?? ????? ????? ?? ???

50
??? ?- ISA

• ????? ??????? ??????? ?? ??? ????? ????? ??? ?-
  ISA (is a)
• ??? ?? ???? ?? ???????? ??????
  (Inheritance Hierarchy) ?????? ??? ?????? ??
  ??????, ??????
• ????? ??????? ?? ?? ?????????
• ????? ??????? ?? ????????? ????? ?????
• ????? ??????? ?? ????????? ????? ???
• ????? ??????? ?? ????????? ??????? ?????? ?????

51
????? ????? ??? ?????

• ?????? ?????? ????? ??? ?????, ???? ????? ???
  ????? ????? ?? ??? ?- ISA
• ????? ?????? ?????? ??????

52
????? ?????? ?????? ?????? ??????

• ???? ????
• ???? ?????? ?? ???
• ???? ?????
• ???? ?????
• ??????? ?? ?????? ??????
• ???? ...

53
??????

• ???? ??????? ??????? ???? ?? ????? ????? ??????
  ?? ?????? ??????? ?? ?????
• ??? ????? ??? ??? ?- ISA
• ???? ????? ?? ????? ?????? ??? ????? ????? ????
  ?????, ?????
• ???? ????? ???? ?? ??? ?????? ???? ?"? ????? ????
  ????? ?? ????? ????? ??????? ?????? ??????,
  ?????? ?????? ????? ?????

54
???? ????? ???? ?? ??? ?????? ??? ???? ????

• Why Is It Difficult to Design a Database Schema?

55
?????? ?????

• ???? ????? ?? ?????? ????? ??????
• ????? ?? ?????
• ?????
• ???? ????? ????? ???? ?????? (??????????)
• ???????
• ????? ????? ?? ?? ?????? (???? NULL)
• ???? ????? ?? ?????????? (?- methods)

56
???? ????? ?? ?????? ????

• A Detailed Explanation
• of These Reasons

57
???? ????? ?? ?????? ????? ??????

• ????? ???? ????? ????? ?????, ?????? ???? ????
  ?????? ??????? ???? ???? ???? ????????? ?????
  ??????? ?? ??????
• ???? ?????? ?????? ?????? ?????? ????? (???? ?"?
  ?????? ??????)
• ????? ???? ????? ?? ?????? ??????? ??????? ??????
  ???? ?????? ???????
• ??????, ????? ??????? ?????? ?????? ?? ?????

58
???? ?????? ?? ????? ?????? ?????? ?? ???????
??? ???????

• ?? ???? ?????? ????? ?????? ????? ?????? (?????
  ????? ??????) ??? ????
• ???? ??????? ????? ?????? ???? ????? ?? ?? ???
• ?????? ???? ????? ?? ????? ?????
• ??????????
• ??? ???

59
?? ???? ??????

• ???? ???? ????? ???? ?? ????? ??? ??????? ????
  ??????
• ?????? ???? ????? ??
• ??????? ?? ????? ????? ????? ???????
• ??????? ?? ?????
• ??????, ??? ???? ?????? ??? ????? ???? ?????
  ?????????
• ????? ????? ???? ?? ???? ??

60
????? ?? ?????

• ????? ????? ?? ??????? ????? (toy examples) ????
  ????? ????? ??? ???? ???? ????? ??????? ??? ???
• ????? ????? ????? ???? ?????? (?? ?? ????)
  ??????? ????? ????? ??????? ?? ?????? ??????
  ?????? ??? ???
• ?????? ????? ?????? ???? "?????" ?? ????? ???????
  ????? ??????? ?? ??? ???????

61
?????

• ??? ?????? ????? ?? ?????? ???????? ???? ISA
  (inheritance), ??? ???? ?? ?????? ????
• ????? ?? ?????????
• ????? ????????? ????? ?????
• ????? ????????? ????? ???
• ????? ????????? ????? ?????
• ????? ????????? ??????? ?????? ????? (?? ?????
  ??? ?' ???? ????? ???? ????? ????? ???? ??? ???
  ????? ????? ??? ????? ????? ?????)
• ????? ????????? ??????? ?????????? (?? ?????
  ????? ??? ???? ????? ???????, ??? ???? ???? ???
  ???? ?????)
• ????? ????????? ??????? ???????????

62
?????
?? ???? ?????? ????? (multiple inheritance)

• ??? ?????? ????? ?? ?????? ???????? ???? ISA
  (inheritance), ??? ???? ?? ?????? ????
• ????? ?? ?????????
• ????? ????????? ????? ?????
• ????? ????????? ????? ???
• ????? ????????? ????? ?????
• ????? ????????? ??????? ?????? ????? (?? ?????
  ??? ?' ???? ????? ???? ????? ????? ???? ??? ???
  ????? ????? ??? ????? ????? ?????)
• ????? ????????? ??????? ?????????? (?? ?????
  ????? ??? ???? ????? ???????, ??? ???? ???? ???
  ???? ?????)
• ????? ????????? ??????? ???????????

???? ?? ?? ????? ??? ???? ??? ?????? ?????, ?? ??
?????? ???????? ?? ?????? ??? ?????
63
???? ????? ????? ???? ?????? (??????????)
??? ???? ???? ??? ?? ?? ????? ??? ????

• ????? ???? ???? ???? ?? ?????? ?????
• ??' ????, ?? ????, ??????, ??? ?? ????? ??????
  ????? ??????? ???????? ????, ??' ??????
  ???? ??????? ???
• ?????, ???? ????? ?????? ?????? ?????
• ??????(??) ??? ???? ?????, ?????, ????? ????????
  (?? ?? ???? ????? ?? ?? ???? ?????? ???? ??? ????
  ??????? ????)
• ??? ???? ??? ??? ??????? ??? ??? ISA?

???? ???? ????? ????
???? ?????? ???? ????
64
???? ????? ????? ???? ?????????? (??????)
?? ????? ??? ????? ???????, ????? ???? ???????
???? ????? ????

• ????? ???? ???? ???? ?? ?????? ?????
• ??' ????, ?? ????, ??????, ??? ?? ????? ??????
  ????? ??????? ???????? ????, ??' ??????
  ???? ??????? ???
• ?????, ???? ????? ?????? ?????? ?????
• ??????(??) ??? ???? ?????, ?????, ????? ????????
  (?? ?? ???? ????? ?? ?? ???? ?????? ???? ??? ????
  ??????? ????)
• ??? ???? ??? ??? ??????? ??? ??? ISA?

65
???? ????? ????? ???? ?????????? (??????)
???? ??? ??? ?????? ???? ????. ????? ???? ???
?????? ??????? ?????? ??? ???

• ????? ???? ???? ???? ?? ?????? ?????
• ??' ????, ?? ????, ??????, ??? ?? ????? ??????
  ????? ??????? ???????? ????, ??' ??????
  ???? ??????? ???
• ?????, ???? ????? ?????? ?????? ?????
• ??????(??) ??? ???? ?????, ?????, ????? ????????
  (?? ?? ???? ????? ?? ?? ???? ?????? ???? ??? ????
  ??????? ????)
• ??? ???? ??? ??? ??????? ??? ??? ISA?

66
???????

• ????? ????? ?????? ???? ????? ?? ???????? ??????
  ????????? ????? ????? ????? ???? ????? ???????
• ??? ???? ????? ???? ????? ???? ??? ????
• ??? ???? ????? ???? ?????? ????? ??? ?????
• ????? ???????? ??? ???"? ??? ???? ?????? ???????
  ???????
• ??? ??? ?????? ?? ????? ?? ??? ?? ??? ???? ????
  ?????? ???? ?? ??????

67
????? ????? ?? ?? ?????? (???? NULL)

• ??? ??? ?? ???????? ???? ????? NULL?
• ?? ???? ?? ?????? ???
• ???? ????? ?? ?????? ????? NULL
• ?? ?????? (???? ????????? ?? ???????) ????? ?????
  ???? ???? ?????? ????? ????? NULL
• ???? NULL ??????? ???? ?????? ?????? ?? ??????
  ???????
• ???? ???? ?? ??????? ????? ???? ???? ?? ???
  ?????????? ????

68
?????

• ??? ????? ?? ?? ????????? ?? CS ???? ????? ??
  ?????
• DEPT CS
• ??? ????? ?? ?? ????????? ?? CS ?? ??? ?????? ???
  ?- CS ???? ????? ?? ?????
• DEPT CS OR DEPT IS NULL
• ????? ???????, ????? ????? ????? ?????? ??? ???
  ???????? ???? modes ???????
• Mode ????? ?? ??????? ???????
• Mode ????? ?? ??????? ????????

?????????? ?????? ???? ?????? ???
69
???? ????? ?? ?????????? (?- methods)

• ???? ???? ?????? ??????????? ???? ???? ?? ??????,
  ???????? ???'
• ???? ????? ???? ?? ?????? ????? ???? ?- CS?
• ?? ???? ?? ???? ???? ???? ???????, ?? ???
  ???????? ???? ????? ???? method ????? ??? ??????
  ???? ?????
• ?? ???? ????? ?????? ???? ???? ?????? ???? ???
• ??????, ????? ????? ???? ??? ???? ???? ????
  ??????????? ??? ???? ???? ?- CS

70
???? ???? ????

• ????? ???? ?????? ????? ?? ?? ?????, ???? ??????
  ????? ????, ??? ??? ?? ????? ??????? ??????
• ??? ????? ???? ???? ???????? ??? ???? ???? ?- CS?
• ?? ??, ??? ???? ???? ?????? ??????? ????? ?????
  ?????????
• ????? ??????? ??? ????? ????? ?????