Bi 3 M hnh ERD v Chun Ho

Nhc li

CSDL l tp hp cc d liu quan h c lu tr di dng bng H thng tp tin phng n c nhng hn ch v d liu d tha, kh kim sot d liu, v khng c kh nng thao tc d liu d dng H thng qun l CSDL c th nh ngha l tp hp cc bn ghi c quan h v tp hp cc cc chng trnh c dng truy cp v thao tc vi cc bn ghi . H thng qun l CSDL l tp hp cc chng trnh m ngi dng c th thc hin lu tr, sa i v rt trch thng tin t CSDL. H thng qun l CSDL quan h ging nh l cc chng trnh phn mm c dng to, bo tr, sa i v thao tc trn CSDL quan h. CSDL quan h lu d liu trn bng. Cc bng c quan h vi nhau bn trong CSDL.RDBMS and Data Management/ Session 2/2 of 15

Cc mc tiu ca bi hc

nh ngha v m t v s m hnh ho d liu Nhn dng v m t cc thnh phn trong m hnh E-R (m hnh quan h thc th) . Nhn dng mi quan h gia cc thc th. Gii thch cc s E-R v l do ti sao chng li hu ch. M t biu , cc k hiu c s dng v v hin th cc mi quan h khc nhau. M t cc dng chun khc nhau

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M hnh ho d liu

M hnh d liu - Mt nhm ca cc cng c nim m m t d liu. Mi quan h ca n v ng ngha. N cng bao gm cc rng buc ton vn m d liu gn b ti. M hnh ho d liu c chia nh thnh ba bc: Conceptual Data Modeling (M hnh d liu nim) Logical Data Modeling (M hnh d liu lun l) Physical Data Modeling (M hnh d liu vt l)RDBMS and Data Management/ Session 2/4 of 15

M hnh Thc th- Mi quan h (ER) 1-4

Cc m hnh c th phn thnh cc nhm khc nhau:

Cc Cc Cc

Human Resource M hnh thc th thuc phn loi u tin. M hnh c da trn tng works in D liu c th c hiu nh l n gin. Production cc i tng trong th gii thc c gi l thc th v cc mi Accounts quan h tn ti gia cc thc th ny.

M hnh E-R bao gm nm thnh phn c bn. l:

Tp thc th m hnh lun l da trn i tng Employee m hnh lun l da trn bn ghi m hnh vt l

Tp thc th Department

Relationship Set Mi quan h (E-R)

Logistics

Thc th -Entity Mi quan h- Relationship Cc thc th Thuc tnh - Attributes Tp Employee-Entity Set thc th Tp quan h -Relationship Set

Cc thc th

Department

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M hnh Thc th- Mi quan h (ER) 2-4

Cc mi quan h c kt hp t mt hoc nhiu thc th. Chng c 3 kiu:

Mi quan hh thn: Cc mi quan h h m hthc Mi quan tam phn: Cc mi mi gia cc ti Mi quan h t nh phn: Cc quan quan tn m th ca cc tp thc th ging nhau c gi l mi gia ti t thn. thuc th ca thcthc khc thuc tn h thc th quan ba gia cc thc cc tp hai th th nhau c tp l mi th khc nhau c gi l quan h cc gi thc quan h tam phn.

nh phn.

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M hnh Thc th- Mi quan h (ER) 3-4Cc mi quan h c th c phn loi da trn nh x tp hp. Cc nh x phn loi khc nhau l: Mt - mt: nh x ny tn ti khi mt thc th ca mt tp thc th c th kt hp vi ch mt thc th ca tp thc th khc. Mt - nhiu: nh x ny tn ti khi mt thc th ca mt tp thc th c kt hp vi nhiu hn mt thc th ca tp thc th khc. VehicleEntity Set

f f fVehicle Customer Entity Set Entity Set

Registration Entity Set

registration

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M hnh Thc th- Mi quan h (ER) 4-4

Nhiu-mt: nh x ny tn ti khi nhiu thc th ca mt tp thc th c kt hp vi mt thc th ca tp thc th khc. Vehicle Nhiu-nhiu: nh x ny tn ti khi s cc thc th ca Entity set tp thc th c kt hp vi s thc th ca tp thc th khc. Location

f h fCustomer Entity Set

Account Entity set Entity Set

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Cc biu Thc th - Mi quan h

Biu E-R l gin trnh by ca m hnh E-R. Cc k hiu c dng cho cc thnh phn khc nhau c th nhn thy trong bng di y:

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Cc biu Thc th - Mi quan h

Cc bc xy dng biu E-R l:

Thu thp tt c cc d liu m cn c m hnh. Nhn bit d liu m c th c m hnh nh l cc thc th trong th gii thc. Nhn bit cc thuc tnh cho mi thc th. Sp xp cc tp thc th yu, cc tp thc th mnh. Sp xp cc thuc tnh ng vai tr kho, cc thuc tnh a tr, cc thuc tnh kt hp, cc thuc tnh dn sut. Xc nh cc mi quan h gia cc thc th. S dng cc k hiu khc nhau v cc thc th, thuc tnh v mi quan h gia chng. Dng cc k hiu thch hp trong khi v cc thuc tnh.

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Chun ho

N l tin trnh t chc d liu mt cch hiu qu trong CSDL.Mc ch ca tin trnh chun ho: Loi b d liu b d tha v m bo d liu ph thuc tr nn ngha. Vo lc u, Codd (1972) trnh by 3 dng chun (1NF, 2NF and 3NF), tt c da trn s ph thuc gia cc thuc tnh ca quan h. Dng chun mt - tr thnh dng chun mt: To ra cc bng ring bit cho mi nhm d liu c lin quan Cc ct ca bng phi c gi tr n. Tt c cc thuc tnh kho phi c xc nhRDBMS and Data Management/ Session 2/11 of 15

Chun ho

Dng chun hai Cc bng t dng chun hai nu:

Chng phi tho cc yu cu ca dng chun mt Chng khng ph thuc mt phn trong bng Cc bng quan h thng qua cc kho ngoi Cc bng phi tho cc yu cu dng chun hai Khng tn ti ph thuc bc cu trong bng.

Dng chun ba - t dng chun ba:

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V d: Invoices

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Chun 1

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Chun 2

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Chun 3

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Tm tt

M hnh ho d liu l qu trnh p dng m hnh d liu thch hp cho cc d liu th. M hnh E-R xem th gii thc nh tp cc i tng c bn v cc mi quan h gia chng. Thc th, thuc tnh, tp thc th, mi quan h v tp mi quan h t nm thnh phn c bn ca m hnh ER. nh x l yu t trong tp hp nhn mnh s cc thc th c kt hp vi nhau. Tin trnh g b s d tha d liu t cc bng ca CSDL quan h c gi l chun ho.

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