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2. Mc ch chn ha CSDL

Biu din c mi quan h trong CSDL

3. Trnh sai st khi thm, xa, sa d liu 4. Trnh phi xy dng li cu trc ca cc quan h khi cn n cc kiu d liu mi 5. Gii thiu

Cc dng chun : C 4 dng chun c bn.

• Dng chun1 (1 Normal Form - 1NF)

6. Dng chun 2 (2 Normal Form - 2NF

7. Dng chun 3 (3 Normal Form - 3NF) 8. Dng chun Boyce-Codd 9. Dng chun 1(1/3)

nh ngha:

• Mt lc quan h Q c gi l t chun 1 nu mi thuc tnh ca Q u lthuc tnh n .

10. Mt lc CSDL c gi l t chun 1 nu mi lc quan h con Qi ca n u t dng chun 1.

11. Thuc tnh n :

• • Gi s c lc quan h Q.
• 12. Mt thuc tnh A c gi l thuc tnh nnu n khng phi l s tch hp ca nhiu thuc tnh khc.

13. Dng chun 1(2/3)

V d:

• Ta c quan h sau :

• • Phan_Cong( MaNV , MaPhong)

• MaPhong khng l thuc tnh n.

14. Quan h Phan_Cong khng t chun 1.

15. Cch khc phc :

• • Phan_Cong( MaNV, MaPhong )

16. Dng chun 1 (3/3)

• Quan h Phan_Cong t chun 1.

17. Dng chun 2(1/3)

nh ngha :

• Mt lc quan h Q c gi l t chun 2 nu :

• • Q t chun 1
• 18. Mi thuc tnh khng kha ca Q iu ph thuc y vo cc kha ca Q.

Mt lc CSDL c gi l t chun 2 nu mi lc con Qi ca n u t chun 2.

19. Dng chun 2(2/3)

V d : Ta c quan h Q sau :

• NhanVien_DuAn ( MaNV, MaDA, TenNV, TenDA, DiaDiemDA, SoGio). Vi cc ph thuc hm:

• • F1: MaNV, MaDU SoGio
• 20. F2: MaNV TenNV

21. F3: MaDA TenDA, DiaDiemDA.

Lc quan h Q ny cha t chun 2 v :

• MaDA TenDA, DiaDiemDA cha t chun 2

22. MaNV TenNV cha t chun 2.

23. Dng chun 2(3/3)

Cch khc phc : Tch lc quan h Q ny thnh cc lc quan h sau :

• Q1 ( MaNV ,TenNV)

24. Q2 ( MaDA , TenDA, DiaDiemDA)

25. Q3 ( MaDA,MaNV ,SoGio)

Lc quan h Q t chun 2.

26. Nhn xt:

• Nu lc quan h Q ch c 1 kha K v K ch c mt thuc tnh th Q t dng chun 2

27. Mt lc d quan h Q chun 2 vn c th cha ng s trng lp thng tin

28. Dng chun 3(1/3)

nh ngha :

• Mt lc quan h Q c gi l t chun 3 nu:

• • Q t chun 2
• 29. Mi thuc tnh khng kha ca Q u khng ph thuc bc cu vo mt kha no ca Q.

• Mt lc CSDL c gi l t chun 3 nu mi lc con Qi ca n u t chun 3.

30. Dng chun 3(2/3)

V d : Xt lc quan h sau :

• NhanVien_DonVi ( MaNV , HoTen, NgaySinh, DiaChi, MADV, TenDV, DiaDiemDV). Vi cc ph thuc hm:

• • F1 : MaNV HoTen, NgaySinh, DiaChi, MaDV, TenDV, DiaDiemDV.
• 31. F2: MaDVTenDV, DiaDiemDV.

• Q cha t chun 3 v cc thuc tnh TenDV, DiaDiemDV ph thuc bc cu vo kha chnh.

32. Dng chun 3(3/3)

Cch khc phc : Tch lc Q thnh cc lc con sau :

• Q1 ( MaNV , HoTen, NgaySinh, DiaChi, MaDV).

33. Q2 ( MADV , TenDV, DiaDiemDV).

Q t chun 3

34. Nhn xt:

• Chnh ph thuc hm bc cu l nguyn nhn dn n tnh trng trng lp thng tin.

35. Dng chun 3 ltiu chun ti thiutrong thit k c s d liu.

36. Dng chun Boyce-Codd (BCNF)(1/2)

L dng chun c tnh n tt c cc kha ng vin nn c nhiu rng buc hn dng chun 3

37. BCNF - Mt quan h dng chun BCNF nu vch nu mi phn t quyt nh ca cc ph thuchm (nm bn trimi tn) l cc kha ng vin. 38. Nhn xt:

• Nu 1 l c quan h Qtdng chun BC thcngtdng chun 3 .

39. Trong 1 l c quan h Qtdng chun BC, vic kim tra ph thuc hm ch yu lkim tra kha ni.

40. Dng chun Boyce-Codd (BCNF)(2/2)

V d:

• T_HNG (SH , NgyH, MKH )

• • F1 = { SHNgyH, MKH }

• CHITIT_H ( SH, MHH , SL ng )

• • F2 = { SH, MHHSL ng }

2 quan h u t dng chun Boyce-Codd.

41. Phng php phn r(1/10)

Qu trnh chun ha 1 l c CSDL:

• Nhm mc ch nng cao cht l ng thit k

42. a cc l c quan h con t dng chun thp ln dng chun cao h n m ti thiu phi l dng chun 3.

Ph ng php phn r l 1 ph ng php dng chun ha 1 l c CSDL

43.

Vic chun ha 1 l c quan h hay 1 l c CSDL phi bo m yu cu: bo ton thng tin

44. Php phn r Q thnh Q 1 , Q 2 , c gi l bo ton thng tin nu:

T Q : T Q= T Q[Q1] |>