07. Data Normalization & More.pdf

Bi 7: Chun ho d liu,

Mt s vn khc

1 EE4509, EE4253, EE6133 HK1 2013/2014 TS. o Trung Kin H Bch khoa H Ni

Chun ho d liu

(data normalization)


Khi nim

Vic thit k mt CSDL quan h l xy dng mt lc quan h

cho php lu tr nhng d liu mong mun

gim thiu tnh d tha d liu

cho php trch xut thng tin d dng

s dng cc dng chun (normal forms): l tp hp cc tiu chun cho CSDL

Chun ho d liu l qu trnh cu trc mt CSDL quan h nhm gim thiu d tha v ph thuc ca d liu (da vo kho v cc ph thuc dng hm)


Cc dng chun

Dng chun th nht (First normal form 1NF): 1970

Dng chun th hai (Second normal form 2NF): 1971

Dng chun th ba (Third normal form 3NF): 1971

Dng chun Boyce-Codd (Boyce-Codd normal form BCNF): 1974

Dng chun th t (Forth normal form 4NF): 1977

Dng chun th nm (Fifth normal form 5NF): 1979

Dng chun th su (Sixth normal form 6NF): 2003


Dng chun th nht 1NF

Mt thc th tho mn 1NF nu n khng c nhm thuc tnh no c lp li

Loi b cc thuc tnh a tr

Phn VD: thc th Order vi phm 1NF v nhm (item_name, item_number, item_price)

lp li 9 ln

y l dng chun n gin nht

Chuyn v 1NF:

Chia cc nhm thuc tnh lp li thnh cc quan h nh hn

S dng thuc tnh kho v kho ngoi

Lin kt 1..n gia cc quan h


Order

id: int

shipdate: date

customer: string

address: string

item_name1: string

item_number1: int

item_price1: int

item_name2: string

item_number2: int

item_price2: int

item_name9: string

item_number9: int

item_price9: int

...

V d: Chuyn mt thc th v 1NF

nh ngha thm quan h ph: OrderItem

Lin kt 1..n

Ch s dng thm kho ngoi: order_id


Order

id: int

shipdate: date

customer: string

address: string

item_name: string

item_number: int

item_price: int

OrderItem

order_id: int

Dng chun th hai 2NF

Mt quan h tho mn 2NF khi v ch khi ng thi:

tho mn 1NF

khng c thuc tnh no c xc nh bi mt tp con ca kho


m-sv lp h-tn

123 CSDL Trn Khnh Linh

123 KTLT Trn Khnh Linh

456 LTM Bill Gates

456 CSDL Bill Gates

456 KTLT Bill Gates

789 VXL L Lin Kit

789 LTM L Lin Kit

Phn VD: quan h bn khng tho mn 2NF v:

h-tn c xc nh hon ton bi m-sv

m-sv l tp con ca kho (m-sv, lp)

Tnh d tha d liu: h tn c lu tr nhiu ln

Chuyn v 2NF

chuyn mt quan h v 2NF:

Tch thnh cc quan h nh hn

S dng lin kt 1..n


M SV H tn

123 Trn Khnh Linh

456 Bill Gates

789 L Lin Kit

M SV Lp

123 CSDL

123 KTLT

456 LTM

456 CSDL

456 KTLT

789 VXL

789 LTM

Ph thuc dng hm

2NF s dng khi nim ph thuc dng hm (functional dependencies): l s tng qut ho ca khi nim kho

nh ngha: Trn mt quan h R, cho R v R l hai tp thuc tnh ca R. Gi ph thuc dng hm vo (k hiu: ) khi v ch khi mi gi tr ca xc nh mt gi tr ca .

Vi v d trc ta c:

m-sv h-tn

Vi khi nim ny, c th nh ngha li 2NF: khng c tp thuc tnh khng kho no ph thuc dng hm vo mt tp con ca thuc tnh kho


Cc tnh cht ca ph thuc dng hm

Cc tin Armstrong

Phn x (ph thuc tm thng): nu th

Tng cng: nu th (, ) (, )

Bc cu: nu v th

Mt s tnh cht khc

Hp: nu v th (, )

Phn r: nu (, ) v th

Gi bc cu: nu v (, ) th (, )


Dng chun th ba 3NF

Mt quan h tho mn 3NF khi v ch khi ng thi:

tho mn 2NF

khng c ph thuc dng hm no vi thuc tnh khng kho

Phn v d:

(Tn ti ph thuc dng hm: tc-gi nm-sinh-tg)


tn sch nm tc-gi nm-sinh-tg

The universe in a nutshell 2001 Stephen Hawking 1942

The Da Vinci code 2003 Dan Brown 1964

A brief history of time 1988 Stephen Hawking 1942

Digital fortress 1998 Dan Brown 1964

The lost symbol 2009 Dan Brown 1964

Chuyn v 3NF

chuyn mt quan h v 3NF (tng t vi 2NF):

Tch thnh cc quan h nh hn

S dng lin kt 1..n

Thm thuc tnh kho ca quan h mi


tn sch nm tc-gi

The universe in a nutshell 2001 Stephen Hawking

The Da Vinci code 2003 Dan Brown

A brief history of time 1988 Stephen Hawking

Digital fortress 1998 Dan Brown

The lost symbol 2009 Dan Brown tc-gi nm-sinh-tg

Stephen Hawking 1942

Dan Brown 1964

Dng chun Boyce-Codd BCNF

BCNF c nh ngha b tr cho 3NF cn c gi l 3.5NF

nh ngha: quan h R tho mn BCNF khi v ch khi: vi mi ph thuc dng hm , mt trong hai iu kin sau tho mn:

l ph thuc dng hm tm thng (tc )

l kho ca R

Tnh cht:

Nu R tho mn BCNF th tho mn 3NF

Ngc li cha chc ng, nhng ch mt s t trng hp


Khung nhn

(views)


Khi nim

Khung nhn l cc quan h o thun tu v mt logic, c to ra da trn cc quan h thc, nhm gip thun tin trong s dng

V d:

Trn CSDL nhn vin, n thng tin v mc lng, a ch nh vi cc ngi dng thng thng

Trn CSDL sinh vin, gp cc quan h SinhVien, LopHoc, DangKy thnh mt quan h o khc d s dng

Vic sa i hay trch thng tin trn khung nhn phi m bo phn nh ng nh khi thao tc trn cc quan h thc


L do chnh dng khung nhn

Ch lm vic trn mt phn ca d liu

C th gp nhiu quan h thnh mt quan h o

To ra cc quan h c kh nng tu bin cao theo nhu cu s dng


Khung nhn khng lu tr thm d liu, m thc thi trn cc quan h thc

H tr thm kh nng bo mt thng tin

n nhng phn d liu khng mun th hin ra bn ngoi

SQL

To khung nhn:

create view tn as select ;

nh ngha ca khung nhn ph thuc vo cu lnh select

Xo khung nhn:

drop view tn;

Sau khi c to, vic truy vn v cp nht d liu ca khung nhn tng t nh vi cc quan h thng


V d (MySQL) mysql> select * from t; +------+-------+ | qty | price | +------+-------+ | 3 | 50 | | 5 | 60 | | 2 | 20 | +------+-------+ 3 rows in set (0.00 sec) mysql> create view t1 as select qty, price as value from t where qty>2; Query OK, 0 rows affected (0.02 sec) mysql> select * from t1; +------+-------+ | qty | value | +------+-------+ | 3 | 50 | | 5 | 60 | +------+-------+ 2 rows in set (0.01 sec) mysql> _


nh ch mc

(indexing)


Khi nim

Vic tm kim vi d liu c sp xp s nhanh hn nhiu so vi d liu khng c sp xp

V d: bi ton tra t in

nh ch mc (indexing) l vic to ra cc cu trc d liu (cy, bng bm,) ph gip tm kim d liu nhanh hn

C th to nhiu index cho mi quan h

Nn to index cho cc thuc tnh hay c dng trong cc iu kin tm kim (mnh where..)

Khng phi iu kin tm kim no cng c th dng c index (VD: tm kim chui con,)


SQL

To index:

create index tn-index

on tn-quan-h(tn-thuc-tnh);

Xo index:

drop index tn-index on tn-quan-h;

Lit k cc index:

(MySQL) show indexes from tn-quan-h;

(SQL Server) exec sp_helpindex tn-quan-h;

Sau khi index c to, vic s dng cc quan h vn nh trc. Vic s dng ti cc index l t ng do DBMS t quyt nh.


V d (MySQL) mysql> select count(*) from thivien_poem where AUTHOR=20; +----------+ | count(*) | +----------+ | 158 | +----------+ 1 row in set (1.74 sec) mysql> create index thivien_poem_AUTHOR on thivien_poem(AUTHOR); Query OK, 40349 rows affected (1 min 14.00 sec) Records: 40349 Duplicates: 0 Warnings: 0 mysql> select count(*) from thivien_poem where AUTHOR=20; +----------+ | count(*) | +----------+ | 158 | +----------+ 1 row in set (0.00 sec) mysql> _


Bi tp

1. Xc nh xem quan h sau thuc dng chun no: ITEM (SKU, PromID, Vendor, Style, Price)

(SKU, PromID) (Vendor, Style, Price)

SKU (Vendor, Style)

2. Chun ho quan h trn v dng cao hn

3. Chn mt kho v lit k cc ph thuc dng hm cho: ITEMS (PONum, ItemNum, PartNum, Desc, Price, Qty)


Documents

07. Data Normalization & More.pdf