Chuong 6 - Distributed Database

5/23/2018 Chuong 6 - Distributed Database

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Distributed Database

TS. Nguyn nh Thun


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* Thit k h thng thng tin c CSDL phn tn

bao gm:- Phn tn v chn nhng v tri t d liu;- Cc chng trnh ng dng ti cc im;- Thit k t chc khai thc h thng trn mng

*nh ngha 1:C s d liu (CSDL) phn tn l tp hp d liu,

m v mt log ictp hp ny thuc cng mt hthng, nhng v mt vt ld liu c phntntrn cc v tr khc nhau ca mt mng my tnh.

3.1 Gii thiu v CSDLPT


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S phn tn d liu(data distribution): d liu phi c phn

tn nhiu ni.S tng quan lun l(logical correlation): d liu ca cc nic s dng chung cng gii quyt mt vn .

V d:- Mt ngn hng c ba chi nhnh cc v tr a l khc nhau.- Ti mi chi nhnh c mt my tnh v mt c s d liu tikhon, to thnh mt ni(site) ca c s d liu phn tn.- Cc my tnh c kt ni vi nhau thng qua mt mngmy tnh truyn thng.- Mt khch hng c th gi tin v rt tin ti cc chi nhnh.



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nh ngha 2: C s d liu phn tnl tp hp d liu c

phn tntrn cc my tnh khc nhau ca mt mng my tnh.Mi ni ca mng my tnh c kh nng x l t tr v c th thchincc ng dng cc b. Mi ni cng tham gia thc hintnht mt ng dng ton cc, m ni ny yu cu truy xut d liu

nhiu ni bng cch dng h thng truyn thng.- S phn tn d liu(data distribution): d liu phi c phntn nhiu ni.- ng dng cc b(local application): ng dng c chy hon

thnh ti mt ni v ch s dng d liu cc b ca ni ny.- ng dng ton cc(hoc ng dng phn tn) (global application/ distributed application): ng dng c chy hon thnh v sdng d liu ca t nht hai ni.



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My tnh 1

TerminalTT

My tnh 3TTT

Mng truynthng

C sd liu 1

My tnh 2

TTT

C sd liu 2

C sd liu 3

Chi nhnh 1 Chi nhnh 2

Chi nhnh 3



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My tnh 1 My tnh 2

My tnh 3

Mng cc b

Trung tm my tnhChi nhnh 1

TTT C s

d liu 1C s

d liu 2

C sd liu 3

Chi nhnh 2TTT

Chi nhnh 3TTT

C s d liu phn tn trn mt mng cc b.



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H thng a x l (multiprocessor system)

My tnhpha sau 1

Mng cc b

My tnh ng dng (pha trc)

C sd liu 1

C sd liu 2

C sd liu 3

Trung tm my tnh

My tnhpha sau 2

My tnhpha sau 3

Chi nhnh 1TTT

Chi nhnh 2TTT

Chi nhnh 3TTT



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Hquntrcsdliuphn tn (DDBMSs)

Chcnng:- Htrvictov botr csdliuphn tn- C cc thnh phntngtnhmthquntrcsdliutptrung- Cc thnh phnhtrtrong vicchuyntidliuncctrmv ngcli.

Thnh phn ca DDBMS:- Qun tr d liu (Database management): DB- Truyn thng d liu (Data Communication): DC

- T in d liu (Data Dictionary): DDdng m t thngtin v s phn tn ca d liu trn mng.- C s d liu phn tn (Distributed Database): DDB



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Localdatabase 1

DB DCDDB

TT T

Site 1

Site 2

Localdatabase 2 DB DC DDB

T

Cc thnh phncamtDDBMS thngmi

T T

DD

DD

3.1 Gii thiu v CSDLPT`


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So snh csdl phn tn v csdl tptrung

Nhn xt: CSDL phn tn khng ngin l nhngs thchinphn tn caCSDL tp trung, biv chng cho php

thitkcc ctrngkhc viCSDL tptrung.

Cc cimtiu biucaCSDL truynthng: iukhintptrung

clpdliu

gimdtha

bitlpv bomtdliu.



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a. iu khin tp trungTrong CSDL tpt rung:

- Khnngiukhintptrung trn ton ngunti nguyn thngtin catchc- Mingdngc cc tptin ring can.

Trong CSDL phn tn,- CSDL phn tn ciukhinvicutrc phn lpdavomt h qun tr CSDL ton cc (c trch nhim trn ton bCSDL phn tn) v hquntrCSDL ccb(c trch nhimviCSDL ccb).- HquntrCSDL ccbc thc mtmcttrcao.- Cc CSDL phn tn c th rtkhc nhau vmc t tr: thon ton ttr,khng c btcmthquntrCSDL tptrungno, nhunhhon ton iukhintptrung.



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b. c lp d liu

Trong sut phn tn:- Vi trong sut phn tn chng ta hiu rng cc chngtrnh ng dng c th s dng CSDL nh l n khng ct chc phn tn.- S chnh xc ca chng trnh khng b nh hng bi

vic dch chuyn d liu t trm ny n trm khc. Tuynhin, tc thc hin ca chng b nh hng.`



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c. GimdthadliuTrong CSDL tptrung:

- Dliudthacgimnmctithiubiv: Skhng tngthch gianhiubnsao cacng mt

tpdliu. Titkim khng gian lu trbngcch loibcc d

tha.Trong CSDL phn tn:- Dthaphctphnv Hotngcacc trnh ngdngc thbtngln khi

d liucsao li ttccc vtr, nitrnh ngdngcnn.

Tnh thngtrccahthngstngln, biv khi cli xy ra mt trm no s khng dng vic thchincc ngdngca trmkhc nud liuc

sao chp li.



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u v nhc im ca h phn tn

u im p ng nhanh hu ht cc ng dng s dng d liu ti

cc trm

Tng cng cc n th ng dng v CSDL m khng lmcn tr ngi s dng hin ti.

Kim sot d liu a phng theo hng hon thin s

tch hp v qun tr d liu t xa.

Tng cng kh nng ca h thng lin quan n s dtha d liu.



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u v nhc im ca h phn tn

Nhc im

Phn mm t v phc tp

Phi x l cc thay i thng bo trong mi a im

Kh kim sot tnh ton vn d liu vi nhiu bn sao d

liu c phn b khp mi ni.

p ng chm nhu cu ca cc trm trong trng hp cc

phn mm ng dng khng c phn b ph hp vi vic

s dng chung.



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Kin trc CSDL phn tn


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3.2 KIN TRC C BN CA CSDL PHN TN

S tng th(Global Schema)

S phn mnh(Fragmentation Schema)

S nh v(Allocation Schema)

CcS

clpvtr

S nh x a phng 1(Local mapping Schema 1)

S nh x a phng n(Local mapping Schema n)

H qun tr CSDL ti v tr 1(DBMS 1)

H qun tr CSDL ti v tr n(DBMS n)

Kin trc tham kho dng cho CSDL phn tn

CSDL aphng 1

(LocalDatabase 1)

CSDL aphng n

(LocalDatabase n)


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3.2 Kin trc c bn ca mt c s d liuphn tn

a. Stngth(GlobalSchema):

Xc nhttccc d liusc lutrtrong csd

liuphn tn cngnh cc d liu khng cphn tn

cc trmtrong hthng.

Stngthcnhnghatheo cch nhtrong CSDL

tptrung.

Trong m hnh quan h,stngthbao gmnhngha

catpcc quan htngth(Global relation) .


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b. Sphn on/ phn mnh(fragment schema):

Miquan htngthc thchia thnh mtvi phnkhnggiao nhau gil phn mnh(fragment).

C nhiucch khc nhau thchinvicphn chia ny

Sphn mnhm tcc nh xgiacc quan htngth v cc on c nh ngha trong s phn mnh

(fragmentation Schema),

Cc oncm tbngtn caquan htngthcngvichmccamnh. Chnghn,Richiul onthi

caquan hR.



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c. Snhv(allocation schema):

Cc onl cc phnlogic camtquan htngthcnhvvtl trn mthay nhiutrm.

S nh v xc nh on d liu no c nh v ti

trmno trn mng.

Ttc cc onc lin ktvi cng mtquan h tng

thR v cnhvticng mttrmj cuthnh nhvtl

quan htngthR titrmj.

Do ta c thnh xmt-mtgiamtnhvtl v mtcp(quan htngth,trm).

Cc nhvtl c thchra bngtn camtquan htng

thv mtchmctrm.



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K hiu Ri ch on/mnh th i ca quan h tng th R

K hiu Rj ch nh vt l ca quan h tng th R titrm j

Tng t nh vy, bn sao ca on i thuc quan h R

ti trm j c k hiu l Rij

d. S nh x a phng (Local mapping schema):

Thc hin nh x cc nh vt l ln cc i tng c

thc hin bi h qun tr c s d liu a phng Tt c cc on ca mt quan h tng th trn cng mt

trm to ra mt nh vt l



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RR1

R2

R3

R4

R11

R2

1

R12

R2

2

R23

R33

R43

Cc onQuan h tng th Hnh nh vt l

R1

(Trm 1 )

R2(Trm 2 )

R3

(Trm 3 )

Cc on v hnh nh vt l ca mt quan h tng th



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3.3 CC C IM CHNH CA H PHN TN

1. Ch ia sti nguyn

cthchinqua mngtruynthng.Mi ti nguyn cn phi c qun l bi mt chngtrnh c giao dintruynthngCc ti nguyn c thctruy nhp,cpnhtmtcch

tin cyv nhtqun.Qunl ti nguyn: bao gmLpkhochdphngttn cho cc lpti nguyn

Cho php ti nguyn c truy nhptniny nnikhcnh xtn ti nguyn vo achtruynthng.


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2. Tnh mTnh mcahthngphn tn l tnh ddng mrng

phncngcan. Mththngcgil c tnh mthphic cc iukinsau: H thng c th to nn bi nhiu loi phn cng vphnmmcanhiunh cung cpkhc nhau.

C thbsung vo cc dchvdng chung ti nguynm khng ph hnghay nhn icc dchvangtnti. Tnh mchon thinbngcch xc nhhay phnnh r cc giao din chnh ca mt h v lm cho n

tngthch vicc nh pht trinphnmm. Tnh mcahphn tn datrn viccung cpcchtruynthng giacc tintrnh v cng khai cc giao dindng truy nhpcc ti nguyn chung.



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3. Khnngsong song

H phn tn hot ng trn mt mng truyn thng cnhiumy tnh, mimy c thc mthay nhiuCPU. C th thc hin nhiu tin trnh trong cng mt thiim. Vic thchin tintrnh theo cchphn chia thi

gian (mtCPU) hay (nhiuCPU).

Khnnglm vicsong song t rong hphn tncthhinqua hai tnh hungsau:

Nhiungisdngngthiara cc lnhhay cctngtc vicc chngtrnh ngdng. Nhiu tin trnh Server chy ng thi, mi tin trnhphipngyu cutcc Clients.



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4. Khnngmrng

Khnngmrngcamthphn tn cctrngbitnh khng thay iphnmmhthngv phnmmngdngkhi hcmrng.

Yu cu cho vic m rng khng ch l m rng phn

cng,vmngm n tritrn cc kha cnhkhi thitkhphn tn.V d: tnsutsdngtrn mngtngt,trnh tnh

trng tcnghnxy ra khi ch c mtServer v phip

ngcc yu cutruy nhpcc file . Ngita nhn bncc file trn mtServer khc v hthngcthitksaocho victhm Server cddng. Mtsgiiphp khcl sdngCache v cc bngsao dliu.



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5.Khnngchuli

Victhitkkhnngchulicc hthngmy tnh da

trn hai giiphp sau:

Dng khnng thay thmboshotng lintcv hiuqu.

Dng cc chng trnh hi phc d liu khi xy ra s

c.



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6. mbot in cyvnhtqun

Hthngyu cutin cynh:

. B mtcadliu

. Cc chcnngkhi phchhngphimbo

. Ngoi ra cc yu cucah thngv tnh nhtqun

cng thhinch: khng c mu thun trong nidung

csdliu.



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7. Tnh trong sut

Tnh trong sut ca mt h phn tn c hiu nh l vic

che khut i cc thnh phn ring bit ca h i vi ngi

s dng v nhng ngi lp trnh ng dng.Cc loi trong sut trong h phn tn:

a.Trong sut phn on (fragmentation transparency)

b.Trong sut v v tr (location transparency)c.Trong sut nh x a phng (local mapping transparency)


3 4 TRONG SUT PHN TN


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a. Trong sut phn on(fragmentation transparency):Khi d liu c phn on th vic truy cp vo CSDL

c thc hin bnh thng nh l cha b phn tn vkhng nh hng ti ngi s dng.V d:Xt quan h tng th NCC (Id, Tn, Tui)v cc phn on c tch ra t n:

NCC1 (Id, Tn, Tui)NCC2 (Id, Tn, Tui)NCC3 (Id, Tn, Tui)

Gi s DDBMS cung cp tnh trong sut v phn on,khi ta c th thy tnh trong sut ny c th hin nh

sau:Khi mun tm mt ngi c Id=Id1th ch cn tm trn

quan h tng th NCC m khng cn bit quan h NCC cphn tn hay khng.

3.4 TRONG SUT PHN TN



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SELECT *

FROM NCCWHERE Id=Id1

DDBMS

NCC1

NCC2

NCC3

V tr1

V tr2

V tr3

Trong sut phn on




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b.Tnh trong sutvvtr(location transparency):

Ngisdngkhng cnbitvvtr vtl cad lium c quyntruy cpncsdliutibtcvtr no.

Cc thao tc lyhoccpnhtmtdliutxa c

tngthchinbihthngtiimara yu cu.

Tnh trong sutvv tr rthu ch, n cho php ngi

sdngbqua cc bnsao d liutntimivtr.

Do c thdi chuynmtbnsao dliutmtvtr ny

nmtv tr khc v cho php to cc bn sao mi m

khng nhhngncc ngdng.




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V d: Viquan h tng thR v cc phn onnh

ni trn nhnggisrngDDBMS cung cptrong sutvvtr nhngkhng cung cptrong sutvphn on.

Xt cu truy vn tm ngi c Id=Id1.

SELECT *

FROM NCC1

WHERE Id=Id1

IF NOT #FOUND THEN

SELECT *FROM NCC2

WHERE Id=Id1




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u tin h thng s thc hin tm kim phn on NCC1

v nu DBMS tr v bin iu khin #FOUND th mt culnh truy vn tng t c thc hin trn phn on NCC2,... y quan h NCC2c sao lm hai bn trn hai v tr2v v tr3, ta ch cn tm thng tin trn quan h NCC2m

khng cn quan tm n v tr no.DBMS

NCC1

NCC2

NCC2

V tr 1

V tr 2

V tr 3

S trong sut v v tr




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c. Trong sut nh x a phng(local mapping transparency): L mt c tnh quan trng trong mt h thng DBMS khng

ng nht ng dng tham chiu n cc i tng c cc tn c lp tcc h thng cc b a phng. ng dng c ci t trn mt h thng khng ng nht

nhng c s dng nh mt h thng ng nht.

DBMS

NCC1

NCC2

V tr 1

V tr 2

S trong sut nh x a phng


3 5 Ph bit CSDL h t CSDL


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3.5 Phn bit CSDL phn tn v CSDL song song+ Kintrc bnhcam hnh song

song: B nh chia s hoc B nhphn tn

+ Cc hqun trCSDL c thitk s dng kin trc bnh lhqun trCSDL song song: tndngcng nghmy song song

+ Kin trc khng chia s: mi bx l c b nh chnh v b nh thcp ring, khng c b nh dngchung, cc bx l giao tipvinhaubng mng tc cao (bus hoc

switch)+ Kin trc khng chia s cngc xem nh mi trng cho CSDLsong song theo tnh ixngv ngnhtcacc nt.

M hnh kin trc khng chia s


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M hnh d liu tp trung

M hnh d liu phn tn

3 6 L i h CSDLPT


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3.6 Li ch ca CSDLPT

Qun l d liu phn tn vi cc mc trong sut

khc nhau:+ Phn tn trong sut hay mng trong sut: chia

thnh cc phntrong sutv tn trong sut

+ Bnsao (replication) trong sut: khincho ngidng khng nhnthysc mtcacc bnsao+ Phn on (fragmentation) trong sut: khinngidng khng nhn thys c mtca cc

phn on(phn ontheo chiudc/ngang)

3 6 L i h CSDLPT (tt)


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Tng tnh tin cy (reliability): l xc sut h thng

chy(khng dng)tithiimxc nh,- Tnh sn sng (availability): l xc suth thngckhnngvnhnh lin tctrong sutmtkhongthigian.

Nng cao nng lchthng: do vicnhvd liulm gimstngtranh giaCPU v cc dchvI/Ov dnnvictrtrong cc mngdinrng.

Ddng mrng.

3.6 Li ch ca CSDLPT (tt)

3 6 L i h CSDLPT (tt)


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Cc chcnngkhc caCSDL phn tn:+ Luvtcadliuphn tn, phn onv bnsao bngvic

mrngcatalog DDBMS+ Tin trnh truy vnphn tn: truy cpcc site txa v truyncc cu truy vnv dliugiacc site thng qua mng

+ Qunl cc giao dchphn tn: nhra cch thchincccu truy vnv giao dch truy cpd liu t xa tnhiu site,ngbv mbotnh ton vn

+ Qunl sao ludliu: quytnhxem truy cpbnsao nov duy tr tnh nhtqun ca cc i tngd liu trong bnsao

+ Khi phcdliuphn tn: khi phctcc site bcrash, cclin ktbhng

+ Bomt: bomqunl trnvntnh bomtcadliuvquyntruy cp/cpphp (authorization/access) cangidng

+ Qunl cc khonmcphn tn

3.6 Li ch ca CSDLPT (tt)

3 7 PHNG PHP THIT K CSDL PHN TN


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3.7 PHNG PHP THIT K CSDL PHN TN

S thit k tng th c s d liu phn tn

Hin nay cha c mt k thut c th no ni mt cchchi tit vic thit k mt CSDL phn tn.

Thit k lc quan h tng th

Thit k phn on

Thit k nh v cc on(To cc nh vt l)

Thit k CSDL vt l

S thit k tng th



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1. Thit k lc quan h tng th:

Thit k cc quan h tng th M t ton b d liu s c dng trong h thng2. Thit k phn on:thc hin chia nh d liu thnh

cc phn.

3. Thit k nh v cc on: l qu trnh thc hin nh x cc on vo cc trmkhc nhau

To cc nh vt l ti cc trm.

Cc on d liu c a vo cc v tr lu tr thchhp vi yu cu hot ng thc t ca h thng.4. Thit k c s d liu vt l:thit k d liu vt l cho

cc quan h ti cc trm




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Cc phng php thit k CSDL phn tn

C 2 phng php thit k CSDL phn tn

Phng php tip cn t trn xung

Phng php tip cn t di ln.




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3.7.1 Phng php thit k t trn xung (Top-Down)

Thit k t tng th n ring bit

Phn r mt h thng ln thnh cc h thng con

Phn tch cc yu cu nhm nh ngha mi trng h thng

Thu thp cc yu cu v d liu v nhu cu x l ca cc

trm c s dng CSDL.




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Thit k view: xy dng khung nhn d liu cho ngi

s dng cc trm.

Thit k mc quan nim: l mt tin trnh kim tra v

xc nh r hai nhm quan h:phn tch thc thv

phn tch chc nng.

+ Phn tch thc th: xc nh cc tp thc th, cc

thuc tnh v cc mi quan h gia chng.

+ Phn tch chc nng: xc nh cc chc nng ca

h thng v a ra cc chc nng c s.




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Thit k phn tn: bao gm hai phn:

+ Thit k phn on

+ Thit k nh v

Thit k lc quan nim a phng: to ra cc

lc mc quan nim ti cc a phng

Thit k vt l: thc hin nh x lc mc quan

nim ti cc a phng ra cc n v lu tr vt l

Quan st v kim tra: kim tra cc giai on ca qu

trnh thit k c s d liu




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3.7.2 Phng php thit k t di ln (Bottom-Up)Nhn xt

Phng php thit k trn xung thc s c hiu qu khixy dng mt h thng mi. Trong thc t, mt s CSDL tn ti trc, c t

chc trong mi trng tp trung v CSDL phn tn cpht trin bng cch lin kt chng li thnh mt CSDLmi thng nht (Cc DBMS cc b khc nhau c sdng)

Cch thit k1. Chn mt m hnh d liu chung m t lc tng

th2. Chuyn mi lc cc btheo m hnh d liu chung

chn3. Tch hp cc lc cc b vo lc tng th


3 8 PHN MNH D LIU


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Phn mnh (theo chiu ngang, dc,kthp),bn

sao (replication), cppht trong CSDL phn tn: M hnh phn on ca mt CSDL l vic nhngha tp cc cch phn on bao gm cc thuctnh v tuple trong CSDL v vic thocc iukin

c xy dng CSDL ban u t cc phn onbng cch s dng cc ton t OUTER UNION(hocOUTER JOIN) v UNION

Numtphn onclutrnhiusite, ta ni

rngphn oncsao lu(replicated)

3.8 PHN MNH D LIU

3 8 1 Phn mnh ngang (horizontal fragmentation)


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- Phn mnh ngang mt quan h tng th n-b R l tch Rthnh cc quan hcon n-bR1, R2, ..., Rksao cho quan hR

c thckhi phclitcc quan hcon ny bngphphp: R = R1R2 ... RkPhn mnhonngang mtquan h l tp con ca cc b

trong quan h.Cc bthucvphn onno th cchra bngiukin

vtnh chtcaquan h.Phn onngang chia ngang mtquan hbngcch nhm

cc dng tothnh tpcon cc b. Phn on ngang c c t vic phn hoch quan h

primary thnh cc cc quan h secondary, cc quan hnylin ktviquan hprimary thng qua kho ngoi.

Phn onngang caquan hR cvitl (R) trong isquan h

3.8.1 Phn mnh ngang (horizontal fragmentation)

3 8 2 Phn mnh dc (vertical fragmentation)


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Phn on dc chia mt quan h theo chiu dc bi cc ct Mi phn on dc ca quan h ch lu cc thuc tnh ca quan h

Phn on dc ca quan h R c vit l trong i s quan h Mt tp cc phn on dc m php chiu danh sch L1,L2,,Lngm tt c cc thuc tnh trong R nhng ch chia s ch thuc tnhkho ca R gi l phn on y ca R

Trong trng hp ny, php chiu danh sch tho:

++ vi mi i j trong ATTTRS(R) l tp cc thuc tnhca R v PK(R) l kho chnh ca R

xy dng li R t cc phn on dc ta s dng ton t OUTERUNION trn phn on dc

- Phn mnh dc mt quan h tng th n-b R l tch R thnh cc quanh con R1, R2, ..., Rk sao cho quan h R c th c khi phc lit cc quan h con ny bng php ni:

R = R1 R2 ..., Rk

3.8.2 Phn mnh dc (vertical fragmentation)

3 8 3 Phn mnh kt hp (hybrid fragmentation)


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3.8.3 Phn mnh kt hp (hybrid fragmentation)

L victhpphn ondcv phn onngang

Quan hban uc thxy dng libngcch pdngcc ton tUNION v OUTER UNION Thng thng, mi phn on ca quan h R ccbngcch thpton tSELECTPROJECT,k

hiuL(C(R)):+ If C = TRUE and L ATTRS(R): phn ondc+ If C TRUE and L = ATTRS(R): phn onngang+ If C TRUE and L ATTRS(R): phn onhnhp

V d v phn mnh d liu


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V d:Xt c s d liu ca mt cng ty phn mm c t

chc nh sau: NHANVIEN (MANV, TENNV, CHUCVU): quan h ny

cha d liu v nhn vin ca cng ty.

TLUONG (CHUCVU, LUONG):quan h ny cha d liu

lin quan v lng v chc v ca nhn vin.

DUAN (MADA, TENDA, NGANSACH):quan h ny cha

d liu v cc d n m cng ty ang thc hin.

HOSO (MANV, MADA, NHIEMVU, THOIGIAN):quan hny cha d liu v h s ca nhn vin c phn cng

thc hin d n).

V d v phn mnh d liu

C s d liu ca mt cng ty my tnh


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NHANVIEN (E) HOSO(G)


MANV TENNV CHUCVU

A1

A2

A3

A4

A5

A6A7

A8

Nam

Trung

ng

Bc

Ty

HngDng

Chin

Phn tch HT

Lp trnh vin

Phn tch HT

Phn tch HT

Lp trnh vin

K s inPhn tch HT

Thit k DL

MANV MADA NHIEMVU THOIGIAN

A1A2

A2

A3

A3

A4A5

A6

A7

A8

D1D1

D2

D3

D4

D2D2

D4

D3

D3

Qun lPhn tch

Phn tch

K thut

Lp trnh

Qun lQun l

K thut

Qun l

Lp trnh

1234

6

12

10

620

36

48

15

MADA TENDA NGANSACH

D1D2D3D4

CSDLCITBOTRPHT TRIN

20000120002800025000

CHUCVU LUONG

K s inPhn tch HT

Lp trnh vinThit k DL

1000

2500

3000

4000

DUAN (J) TLUONG (S)

V d v phn mnh d liu


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V d v phn mnh d liu

V d v phn mnh d liu


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V d v phn mnh d liu

3.8.4 Bn sao (replication) v cp pht (allocation)


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3.8.4 Bn sao (replication) v cp pht (allocation)

Bn sao c dng tng tnh sn sng (availability) ca dliu

+ Vic sao lu ton b d liu ca tt c cc site trong h phntn s to ra bn sao y ca CSDL phn tn+ Mi phn on c lu ng mt site s khng c bn

sao (khng c tnh hon nguyn). Trong trng hp ny mi

phn on c tch ri ra tr kho chnh c lp li trongphn on dc (hoc hn hp)+ Mt s phn on ca CSDL c th c sao lu trong khi

mt s khc li khng: sao lu tng phn Mi phn on (hoc mi bn sao phn on) cn c ch

nh vo mt site ring bit trong h phn tn. Cng vic nyc hi l phn tn d liu (data distribution) hay cp pht dliu (data allocation)

3.9 Cp pht ti nguyn trong h phn tn


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3.9.1 Bi ton cp pht (allocation problem):

Gi s c mt tp cc mnh F = {F1, F2, ..., Fk } v mtmng my tnh bao gm cc v tr S= {S1, S2, ..., Sm }trn c mt tp cc ng dng Q={Q1, Q2, ..., Qq }ang thc thi.

Hy tm mt phn phi ti u cc mnh F cho cc vtr S.



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59

a. Chi ph nh nht: hm chi ph bao gm:

Chi ph lu mi mnh d liu Fiti v tr Sj Chi ph truy vn Fiti v tr Sj Chi ph cp nht Fi ti tt c cc v tr c cha n

Chi ph truyn d liu.Bi ton cp pht s tm mt lc cp pht vi hm chi ph

l cc tiu.

b. Hiu qu: chin lc cp pht c thit k nhm cc tiuha thi gian thc hin v tng ti a lu lng h thng ti

mi v tr.

3 9 Cp p t t guy t o g p tMt phn phi c gi l ti u nu tha mn hai yu t sau:



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60

Bi ton cp pht tng qut, k hiu DAP (Database

Allocation Problem), l mtbi ton NP-y. V thhuhtcc nghin cucdnh cho victm ra ccc

thut gii heuristic c c li gii ti u cho loi bi

ton ny. Hinnay chac mtm hnh heuristic tngqut no nhn

mt tpcc mnhv sinh ra mtchin lccppht gn

tiungvicc rng buccho trcm chmiara

mt s gi thit n gin ha v d p dng cho mt s

cch tvnngin.

p p g y g p



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3.9.2 Thng tin cp pht

giai on cp pht, chng ta cn cc thng tin nh lngv c s d liu, v cc ng dng chy trn , v cu trc

mng, v kh nng x l v gii hn lu tr ca mi v tr

trn mng.a. Thng tin v c s d liu

b. Thng tin v ng dng

c. Thng tin v v tr

d. Thng tin v mng

p p g y g p

3.10 X L TRUY VN TRONG CSDL PHN TN


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+ Vai tr cath xl vntin phn tn l nh xcu truy vncpcao trn mtCSDL phn tn vo mtchuicc thao tc cais

quan htrn cc mnh,thhinccbc:- Cu truy vnphicphn r thnh mtchuicc php ton

quan hcgil vntin is.- Th hai, d liu cn truy xutphi c ccb ha cc

thao tc trn cc quan hcchuynthnh cc thao tc trndliuccb(cc mnh).- Cui cng cu truy vn i s trn cc mnhphi c m

rngbao gmcc thao tc truynthng v ctiuha

hm chi ph l thpnht.+ Hm chi ph munni ncc tnh ton nh thao tc xutnhp

a,ti nguyn CPU, v mngtruynthng.



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63

1. Bi ton x l vn tin C hai phng php ti u ha c bn c s dng trong

cc b x l vn tin:- Phng php bin i i s- Chin lc c lng chi ph.

Phng php bin i i s n gin ha cc cu vn tinnh cc php bin i i s nhm h thp chi ph tr licu vn tin, c lp vi d liu thc v cu trc vt l cad liu.

Nhim v chnh ca th x l vn tin quan h l bin icu vn tin cp cao thnh mt cu vn tin tng ng cp thp hn c din t bng i s quan h. Vic bini ny phi t c c tnh ng n ln tnh hiu qu.



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64

Th d 3.1:Xt mt tp con ca lc CSDL c cho

NV( MNV, TnNV, Chc v)PC (MNV, MDA, Nhim v, Thi gian)

V mt cu truy vn n gin sau:Lit k tn ca cc nhn vin hin ang qun l mt d n

Biu thc truy vn bng php tnh quan h theo c php caSQL l:

SELECT TnNVFROM NV, PC

WHERE NV.MNV=PC.MNV

AND Nhimv=Qunl



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65

Th d 3.1:Hai biu thc tng ng trong i s quan h do bin i chnh xc

t cu vn tin trn l:TnNV( Nhimv=Qunl NV.MNV=PC.MNV (NV x PC))

v

TnNV(NV|>


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Th d 3.2:

Th d ny minh ha tm quan trng ca vic chn la v tr v cch

truyn d liu ca mt cu vn tin i s. Chng ta xt cu vn tin cath d trn:

TnNV(NV|> E3(NV)

PC1=MNV E3(PC)

PC2=MNV E3(PC)

Cc mnh PC1, PC2, NV1, NV2 theo th t c lu ti cc v tr 1, 2,3 v 4 v kt qu c lu ti v tr 5


67/114

67


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68

Mitn tvtr i nvtr j c nhn R chra rngquan hRcchuyntv tr i nvtr j. Chinlca) sdngskin l cc quan hcphn mnh theo cng mt cch thchinsong song cc php ton chnv ni. Chinlcbtptrung ttccc dliutivtr luktqutrckhi xlcu truy vn.



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69

Sdngm hnh chi ph ngin,gis:

- Thao tc truy xutmtb(tuple access) ck hiul tupacc, l mtnvv thao tc truynmtb(tupletransfer) tuptrans l 10 nv.

- Cc quan hNV v PC tngngc 400 v 1000b,v c 20 gim cdn thngnhtcho cc vtr.

- Cc quan h PC v NV c gom ccb tngng

theo cc thuc tnh Nhimv v MNV. V vy c thtruy xuttrctipnccbcaPC datrn gi trcathuctnhNhimv(tngngl MNV cho NV)



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70

* Tng chi ph ca chin lc a c th c tnh nh sau:

1.To ra PC bng cch chn trn PC cn (10+10)* tupacc = 20

2. Truyn PC n v tr ca NV cn (10+10)*tuptrans = 200

3. To NV bng cch ni PC v NV cn (10+10)*tupacc*2 = 40

4. Truyn NV n v tr nhn kt qu cn (10+10)*tuptrans = 200

Tng chi ph 460* Tng chi ph cho chin lc b c th c tnh nh sau:

1. Truyn NV n v tr 5 cn 400*tuptrans = 4.000

2. truyn PC n v tr 5 cn 1000*tuptrans =10.000

3. To ra PC bng cch chn trn PC cn 1000*tupacc = 1.0004. Ni NVv PC cn 400*20*tupacc = 8.000

Tng chi ph l 23.000



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71

- Ch s nh gi tiu dng ti nguyn l tng chi ph (totalcost) phi tr khi x l truy vn.- Tng chi ph l tng thi gian cn x l cc php tonvn tin ti cc v tr khc nhau v truyn d liu gia ccv tr.

- Mt cng c khc l thi gian p ng ca cu vn tin, lthi gian cn thit chy cu vn tin.- Trong mi trng CSDL phn tn, tng chi ph cn phigim thiu l chi ph CPU, chi ph xut nhp v chi ph

truyn.



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72

- phctpcacc php ton quan h:+ Cc php ton chn,Chiu(Khng loibtrng lp)c phctpl O(n);+ Cc php chiu(C loibtrng lp),trng lp,ni,nina,chia c phctpl O(n*logn);

+ Tch Descartes c phctpl O(n2

)(Nbiuthlclngcaquan hnuccbthu cclpvinhau)

nhgi:

- Cc thao tc c tnh chnlalm gimilclngcnphithchintrctin.- Cc php ton cnphicspxptrnh thchintch Descartes hoclithchinsau.

3.11 X l truy vn trong mi trng phn tn


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73

Lc tngth

Truy vn mnh c ti u vi cc php ton truyn thng

Ti u ho cc b

Cc truy vn cc b ti u

S phn lp chung cho x l truy vn phn tn

Cc trma phng

Cu truy vn phn tn

Phn r truy vn

Truy vn i s trn cc quan h phn tn

nh v d liu

Truy vn mnh

Ti u ho ton cc

Trmiu

khin

Lc phnmnh

Cc thng ktrn cc mnh

Lc aphng



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74

Phn r truy vnGiai onny chia lm bnbc: chunho, phn tch, loi

bdthav vitli.1. ChunhoMc ch: chuyn i truy vn thnh mt dng chun

thun licho cc xl tiptheo.

Vi SQL, c hai dng chun cho cc v t trong mnh WHERE l:Dngchunhi l hi() canhngphp ton tuyn():

(p11p12... p1n) ... (pm1pm2... pmn)

Dngchuntuynl tuyn() canhngphp ton hi():(p11p12 ... p1n) ... (pm1pm2... pmn), trong pij

l cc biuthcnguyn t.

I S MNH


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75

Bng cc tng ng logic thng dngt T= hng ng, F = hng sai

1. pF F

2. pT T

3. pF p

4. pT p5. pp p

6. pp p

7. (p) p

8. pp F9. pp T

10.pq qp

I S MNH


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76

Bng cc tng ng logic thng dng(tt)

11. pq qp12. (pq)r p(qr)

13. (pq)r p(qr)

14. p(qr) (pq)(pr)

15. p(qr) (pq)(pr)16. (pq) pq

17. (pq) pq

18. (pq) (pq)

19. p ( p q ) = p

20. p ( p q ) = p



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77

V d minh ha: xt CSDL cng ty phn mm cho

T cc quan h: E= E (MANV, TENNV, CHUCVU) v

G= HOSO (MANV, MADA, NHIEMVU, THOIGIAN).Xt truy vn:Tm tn cc nhn vin lm d n c m s J1 vi thi gian 12

hoc 24 thng .

Truy vn trn c biu din trong SQL:

SELECT E. TENNVFROM E, G

WHERE E.MANV= G.MANV

AND G.MADA=J1

AND THOIGIAN=12 OR THOIGIAN=24

iu kin trong dng chun hi l:

E.MANV=G.MANV G.MADA=J1 (THOIGIAN=12 THOIGIAN=24)

iu kin trong dng chun tuyn l:

(E.MANV=G.MANV G.MADA=J1 THOIGIAN=12)

(E.MANV=G.MANV G.MADA=J1 THOIGIAN=24)



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78

2. Phn tch

Mc ch: Pht hin ra nhng thnh phn khng ng (sai

kiu hoc sai ng ngha) v loi b chng sm nht nu c th.Truy vn sai kiu:nu mt thuc tnh bt k hoc tn quan

h ca n khng c nh ngha trong lc tng th, hocphp ton p dng cho cc thuc tnh sai kiu.

V d: truy vn di y l sai kiuSELECT E#FROM EWHERE E.TENNV > 200

v hai l do: Thuc tnh E# khng khai bo trong lc Php ton >200 khng thch hp vi kiu chui ca thuctnh E.TENNV



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79

Truy vn sai ng ngha:nu cc thnh phn ca nkhng tham gia vo vic to ra kt qu.

xc nh truy vn c sai v ng ngha hay khng, ta

da trn vic biu din truy vn nh mt th gi l th

truy vn. th ny c xc nh bi cc truy vn lin quan

n php chn, chiu v ni. Nu th truy vn m khnglin thng th truy vn l sai ng ngha



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80

tht ruy vn:

C mtnt dng biudincho quan hktqu Cc nt khc biudincho cc ton hngtrong cu truy vn(cc

quan h)

Cnhnigiahai nt m khng phi l nt ktquth biudin

mtphp ni. Cnhc nt chl nt ktquth biudinmtphp chiu.

Mtnt khng phil nt ktquc thcgn nhn biphp

chnhocphp tni(seft-join: nicaquan hvichnh n).

thktni: L mtthcon cathtruy vn(join graph), trong chc

php ni.



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81

V d: T cc quan h E=E (MANV, TENNV, CHUCVU) v G =

HOSO (MANV, MADA, NHIEMVU, THOIGIAN) v J=DUAN

(MADA, TENDA, NGANSACH).Hy xc nh Tn v nhim v cc lp trnh vin lm d n

CSDL c thi gian ln hn 3 nm.

Truy vn SQL tng ng l:

SELECT E.TENNV, G.NHIEMVU

FROM E, G, JWHERE E.MANV=G.MANV

AND G.MADA.= J.MADAAND TENDA=CSDLAND THOIGIAN36AND NHIEMVU=LTRINH



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82

G.MANV=G.MANV G.MANV=J.MANV

E J(b) th kt ni tng ng

G

th truy vn v th kt ni tng ng

THOIGIAN 36

E.MANV=G.MANV G.MADA=J.MADA

CHUCVU= Lp trnh

TENDA=CSDL

E JG.NHIEMVU

E.TENNV

(a) th truy vn

G

Ktqu



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83

Xt cu truy vnSQL tngng:

SELECT E.TENNV, NHIEMVU

FROM E, G, JWHERE E.MANV=G.MANV

AND TENDA=CSDL

AND THOIGIAN 36

AND CHUCVU=Lptrnh

Truy vn ny l sai ng ngha v th truy vn ca n khng lin thng.

THOIGIAN 36

E.MANV=G.MANV

thiu AND G.MADA=J.MADA

CHUCVU= Lp trnh

TENDA=CSDL

G

E J

Kt qu

G.NHIEMVU

E.TENNV

th truy vn



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84

3. Loi b d tha iu kin trong cc truy vn c th c cha cc v t d

tha. Mt nh gi s si v mt iu kin d tha c th dn

n lp li mt s cng vic. S d tha v t v d tha cng vic c th c loi b

bng cch lm n gin ho cc iu kin thng qua cclut lu ng sau:1. p pp 2. p true true3. p pp 4. p p false

5. p true p 6. p p true7. p false p 8. p1(p1p2) p19. p false false 10.p1(p1p2) p1

V d: n gin ho cu truy vn sau:



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85

SELECT E.CHUCVUFROM E

WHERE (NOT(E.CHUCVU=Lp trnh)AND (E.CHUCVU=Lp trnh ORE.CHUCVU=K s in)ANDNOT(E.CHUCVU=K s in)OR E.TENNV=Dng

t p1:, p2:,

p3: .Cc v t sau mnh WHERE c m t li:p: (p1 (p1 p2) p2) p3((p1 p1 p2) (p1 p2 p2)) p3 (p dng lut 7)((false p2) (p1 false) )p3 (p dng lut 5)

(false false ) p3 (p dng lut 4) P3Vy cu truy vn c bin i thnh:SELECT E.CHUCVUFROM E

WHERE E.TENNV=Dng



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86

4. Vit li

Bc ny c chia lm hai bc con nh sau: Bin i trc tip truy vn php tnh sang i s quan h.

Cu trc li truy vn i s quan h ci thin hiu qu

thc hin. i s quan h l mt cy m nt lbiu din

mt quan h trong CSDL, cc nt khng ll cc quan h

trung gian c sinh ra bi cc php ton i s quan h.



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87

Cch chuyn mt truy vn php tnh quan h thnh mt cy

i s quan h:

Cc nt l khc nhau c to cho mi bin b khc nhau

(tng ng mt quan h). Trong SQL cc nt l chnh l

cc quan h trong mnh FROM.

Nt gc c to ra bi mt php chiu ln cc thuc tnhkt qu. Trong SQL nt gc c xc nh qua mnh

SELECT.

iu kin (mnh WHERE trong SQL) c bin i

thnh dy cc php ton i s thch hp (php chn, ni,php hp, v.v...) i t l n gc, c th thc hin theo th

t xut hin ca cc v t v cc php ton.



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88

V d:

Truy vn Tm tn cc nhn vin khng phi l Dng, lm

vic cho d n CSDL vi thi gian mt hoc hai nm.

Biu din truy vn ny trong SQL l:

SELECT E.TENNVFROM J, G, E

WHERE G.MANV=E.MANV

AND G.MADA= J.MADA

AND E.TENNV Dng

AND J.TENDA= CSDL

AND (THOIGIAN=12 OR THOIGIAN=24)



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89

NHANVIEN (E) HOSO(G)MANV TENNV CHUCVU

A1

A2

A3

A4

A5

A6

A7

A8

Nam

Trung

ng

Bc

Ty

Hng

Dng

Chin

Phn tch HT

Lp trnh vinPhn tch HT

Phn tch HT

Lp trnh vin

K s in

Phn tch HT

Thit k DL

MANV MADA NHIEMVU THOIGIAN

A1A2

A2

A3

A3

A4A5

A6

A7

A8

D1D1

D2

D3

D4

D2D2

D4

D3

D3

Qun lPhn tch

Phn tch

K thut

Lp trnh

Qun lQun l

K thut

Qun l

Lp trnh

1234

6

12

10

620

36

48

15

MADA TENDA NGANSACH

D1D2D3D4

CSDLCITBOTRPHT TRIN

20000120002800025000

CHUCVU LUONG

K s inPhn tch HT

Lp trnh vin

Thit k DL

1000

2500

3000

4000

DUAN (J) TLUONG (S)



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90

SELECTE.TENNV

FROM J, G, E

WHEREG.MANV=E.MANV

ANDG.MADA= J.MADA

ANDE.TENNV Dng

ANDJ.TENDA= CSDL

AND(THOIGIAN=12 OR

THOIGIAN=24)



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91

6 lutbiniphp ton isquan h:Mcch: dng binicy isquan h thnh cc

cy tngng(trong c thc cy tiu).Gi s R, S, T l cc quan h, R c nh ngha trn tonb thuc tnh A={A1, ..., An}, S c nh ngha trn ton bthuc tnh B={B1, ..., Bn}.

1.Tnh giao hon ca cc php ton hai ngi:Php tch Decartes v php ni hai quan h c tnh giao hon.i. R S S R ii. R S S R

2. Tnh kt hp ca cc php ton hai ngi:Php tch Decartes v php ni hai quan h c tnh kt hp.i. (RS) T R (ST) ii. (R S) T R (S T)



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3. Tnh lu ng ca nhng php ton mt ngi

Dy cc php chiu khc nhau trn cng quan h c thp thnh mt php chiu v ngc li:

A(A(R)) A(R) A, AR v A A Dy cc php chn khc nhau trn cng mt quan

h, vipil mt v t c gn vo thuc tnhAi, c th

c t hp thnh mt php chn.

)())(( )()()()( 22112211 RR ApApApAp

)( ii Ap



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93

4. Php chn giao hon vi php chiu

NuApl thnh vin ca {A1, ..., An}, biu thc trn tr thnh

5. Php chn giao hon vi nhng php ton hai ngi Php chn vi php nhn: Php chn vi php ni:

Php chn vi php hp: Nu R v T cng b thuc tnh.

S)()( ),()()( ),( kiik

B

i

Ai BAApAp RSR

)))((())(( ,,...,)(,...,)(,..., 111 RR pnpnpn AAAApAAApAA

))(())(( ,,...,)()(,..., 11 RR pnppn AAAApApAA

SRSRpp ApAp

)()( )()(

)()()( )()()( TRTR iii ApApAp



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94

)()()( ''),p(A ),ip(AiSRSR BABC

jBj

6. Php chiu giao hon vi nhng php ton hai ngi Php chiu v tch Decartes:

Nu C=AB vi AA, BB, v A, B l tp cc thuc tnhtrn quan h R, S ta c:

Php chiu v php ni:

Php chiu v php hp:

Ch :Vic s dng su lut trn c kh nng sinh ra nhiucy i s quan h tng ng nhau. Vn l xc nhcho c cy ti u.

)()()( '' SRSR BAC

)()()( '' SRSR BAC



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95

Ch :Trong giai on ti u, s so snh cc cy c th thc hin

da trn chi ph d on ca chng. Tuy nhin, nu slng cc cy qu ln th cch tip cn ny s khng hiuqu. Chng ta c th dng 6 lut trn cu trc li cy,nhm loi b nhng cy i s quan h ti.

Cc lut trn c th s dng theo bn cch nh sau: Phn r cc php ton mt ngi, n gin ha biu thc truyvn .

Nhm cc php ton mt ngi trn cng mt quan h gim s ln thc hin.

Giao hon cc php ton mt ngi vi cc php ton haingi u tin cho mt s php ton (chng hn phpchn).

Sp th t cc php ton hai ngi trong thc hin truy vn.



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96

V d: Cu trc li cy truy vn v d trn, cho ra cy kt qu tt hn cyban u.

tuy nhin vncn xa cy ti u



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2. nh v d liu phn tn-Ti u ha cc b

Lp nh v bin i mt truy vn i s quan h tng ththnh mt truy vn i s c biu th trn cc mnh vt l.

S dng thng tin c lu tr trn cc lc phn mnh nh v.

Chng trnh i s quan h xy dng li quan h tng tht cc phn mnh ca n gi l chng trnh nh v.

Truy vn c c t chng trnh nh v gi l truy vn banu.

Ch : Trong phn di y, vi mi kiu phn mnhchng ta s biu din mt k thut rt gn sinh ra truyvn c ti u v n gin ho.



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98

1. Rt gn theo phn mnh ngang nguyn thuXt quan h E(MANV,TENNV,CHUCVU). Tch quan h ny

thnh ba mnh ngang E1, E2v E3nh sau:E1=MANVE3(E) E2=E3< MANVE6(E) E3=MANV > E6(E)

Chng trnh nh v cho quan h E: E = E1E2E3.

Dng ban u ca bt k truy vn no c xc nh trn El c c bng cch thay th n bi E1E2E3. Vic rt gn cc truy vn trn cc quan h c phn

mnh ngang bao gm vicxc nh cu truy vn, sau khi cu trc li cy con. iu ny s sinh ra mt s quan h

rng, v s loi bchng. Phn mnh ngang c th c khai thc lm n gin c

php chn v php ni.



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a. Rt gn vi php chn: cho mt quan h R c phnmnh ngang thnh R1, R2,..., Rn vi

Lut 1: nu xR : (pi(x) pj(x)).Trong ,pi, pjl v t chn, x l b d liu, p(x) l v t p chim gi x.V d: Hy rt gn truy vn

SELECT *FROM EWHERE MANV=E5

Vi E c tch thnh ba mnh ngang E1, E2v E3:E1=MANVE3(E) E2=E3< MANVE6(E) E3=MANV > E6(E)

)( jp Rj

)(RRjpj



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MANV=E5 MANV=E5

E1 E2 E3E2

(a) Truy vn ban u (b) Truy vn rt gn

Rt gn bng cch s dng tnh cht giao hon php chn vi phphp, chng ta thy v t chn i lp vi v t E1 v E3 nn sinh ra cc

quan h rng.

E1=MANV E3(E)E2=E3< MANV E6(E)

E3=MANV > E6(E)



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b. Rt gn vi php ni

Cc php ni trn quan h c phn mnh ngang cth n gin khi chng c phn mnh theo thuc tnh ni.

Vic rt gn c thc hin da trn tnh phn phi gia

php ni v php hpv loi b cc php ni v ch. Vi tnh cht, (R1R2) R3= (R1 R3) (R2 R3) , Ril

cc phn mnh. Chng ta c th xc nh c cc php

ni v ch ca cc mnh khi cc iu kin ni mu thunnhau. Sau , dng lut 2 di y loi b cc php ni

v ch.



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102

Lut 2: Ri Rj=nu xRi, yRj : (pi(x)pj(y)). Trong Ri, Rjc xc nh theo cc v t pi, pjtrn cng thuctnh.

Nhn xt:

Vic xc nh cc php ni v ch c thc hin bngcch ch xem xt cc v t mnh.

Truy vn rt gn khng phi lun tt hn hoc n gin hn

truy vn ban u. Mt thun li ca truy vn rt gn l nhng php ni c th

thc hin song song.



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103

V d: Gi s quan h E c phn mnh thnh cc mnh

E1=

MANV E3(E) E

2=

E3< MANV E6(E) E

3=

MANV > E6(E)

Quan h G c phn lm hai mnh:

G1=MANVE3(G) v G2=MANV>E3(G).

Nhn xt:

E1v G1c nh ngha bi cng v t. V t nh ngha G2l hp ca cc nh ngha ca nhng v

t E2v E3.

Xt truy vnSELECT *

FROM E, G

WHERE E.MANV=G.MANV



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104

MANV

MANV

E1 E3E2 G1 G2

(a) Truy vn ban u

MANV MANV

E1 E2E3G1 G2

G2

(b) Truy vn rt gn

Hnh 4.8: S rt gn phn mnh ngang vi php ni

E1=MANV E3(E) E2=E3< MANV E6(E) E3=MANV > E6(E)

G1=MANVE3(G) G2=MANV>E3(G).

E G = (E1E2E3) (G1G2)

= (E1 G1)(E1 G2)(E2 G1)(E2 G2)(E3 G1)(E3 G2)

= (E1 G1) (E2 G2) (E3 G2)



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105

2. Rt gn phn mnh dc Chc nng ca vic phn mnh dc l tch quan h da

vo thuc tnh ca cc php chiu. V php ton xy dng li i vi phn mnh dc l ni,

nn chng trnh nh v mt quan h c phn mnhdc l ni ca cc mnh trong vng thuc tnh chung.

V d: Quan h E c phn mnh dc thnh E1, E2, vithuc tnh kho MANV c lp li nh sau:E1= MANV,TENNV(E) v E2= MANV,CHUCVU(E)Chng trnh nh v l: E = E1 MANVE2 Cc truy vn trn phn mnh dc c th rt gn bng cch

xc nh cc quan h trung gian v ch v loi b cc cycon cha chng.

Cc php chiu trn mt phn mnh dc khng c thuctnh chung vi cc thuc tnh chiu (ngoi tr kha ca

quan h) l v ch mc d cc quan h l khc rng



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106

Lut 3: D,K(Ri) l v ch nu DA=. Trong , quan h Rxc nh trn A={A1, ...,An}; R = A(R), AA , K l kho ca

quan h, KA, D l tp cc thuc tnh chiu, D A.V d: Vi quan h E c phn mnh dc nh sau:E1= MANV,TENNV(E) v E2= MANV,CHUCVU(E)

Xt truy vn SQL:

SELECT TENNVFROM E

TENNV TENNV

MANV

E1 E2 E1

(a) Truy vn ban u (b) Truy vn rt gn

Hnh 4.9: Rt gn i vi vic phn mnh dc

Nhn xt: php chiu trn E2l v ch v TENNV khng c trong E2,nn php chiu ch cn gn vo E1

3 Rt gn theo phn mnh gin tip



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107

3. Rt gn theo phn mnh gin tip S phn mnh ngang gin tip l mt cch tch hai quan h

vic x l ni ca cc php chn v php ni Nu quan h R ph thuc vo s phn mnh ngang gin tip

nh quan h S, th cc mnh ca R v S, m c cng gi trthuc tnh ni s c nh v ti cng trm. Ngoi ra, S c thc phn mnh ty thuc vo v t chn.

Khi cc b ca R c t tu theo nhng b ca S, th s phnmnh gin tip ch nn s dng mi quan h mt nhiu t SR(i.e. vi mt b ca S c th ph hp vi n b ca R, Nhng vimt b ca R ch ph hp vi mt b ca S).

Truy vn trn cc phn mnh gin tip cng c th rt gn

c, nu cc v t phn mnh mu thun nhau th php ni sa ra quan h rng.

Chng trnh nh v mt quan h c phn mnh nganggin tip l hpca cc mnh.



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108

V d: Cho mi quan h mt nhiu t E n G, quan hG (MANV, MADA, NHIEMVU, THOIGIAN) c th c phn

mnh gin tip theo nhng lut sau:G1 = G MANVE1 v G2 = G MANVE2.Trong E c phn mnh ngang nh sau:E1= CHUCVU=Lp trnh(E) v E2= CHUCVULp trnh(E)

Chng trnh nh v cho mt quan h c phn mnhgin tip l hp ca cc mnh G=G1G2.

rt gn cc truy vn trn phn mnh gin tip ny, php

ni s a ra quan h rng nu cc v t phn mnh muthun nhau.

V d v t G1v E2mu thun nhau, nn G1 E2=.

G1 = G MANVE1 v G2 = G MANVE2.E1= CHUCVU=Lp trnh(E) v E2= CHUCVULp trnh(E)


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109

V d: Xt truy vnSELECT *

FROM E, GWHERE G.MANV=E.MANV

AND CHUCVU=KS c kh

CHUCVU=KS c kh

(b) Truy vn sau khi y php chn xung

MANV

G1 G2 E2

CHUCVU=KS c kh

MANV

G1 G2

E1 E2(a) Truy vn ban u

Ch : (G1G2 ) CHUCVU=ksc kh(E2)= (G1 CHUCVU=ksc kh(E2)) (G2 CHUCVU=ksc kh(E2))


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Nhn xt:

Truy vn ban u trn cc mnh E1, E2, G1v G2tng ng hnh 4.10a. Bng cch y php chn xung cc mnh E1v E2, c truy vn rtgn hnh 4.10b.

Phn phi cc php ni vi php hp, chng ta thu c cy hnh4.10c.

Cy con bn tri a ra mt quan h rng, nn cy rt gn c ctron hnh 4.10d.

Hnh 4.10: Rt gn ca phn mnh gin tip

MANV

CHUCVU=KS c kh

G1 G2E2

(c) Truy vn sau khi y php hp ln

MANV

CHUCVU=KS c kh

E2 G2

MANV

CHUCVU=KS c kh

E2

(d) Truy vn rt gn

4 Rt th h h h h



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111

4. Rt gn theo phn mnh hn hp

S phn mnh hn hp l s kt hp gia phn dc v

phn mnh ngang. Mc ch ca phn mnh hn hp l h tr cc truy vn lin

quan n php chiu, php chn v php ni

Chng trnh nh v cho mt quan h phn mnh hn

hp l php hp v php ni ca cc mnh.

V d: Xt quan h E c phn mnh hn hp nh sau:

E1=MANV E4(MANV,TENNV(E)), E2=MANV > E4(MANV,TENNV(E))

E3=MANV,CHUCVU(E)

Chng trnh nh v l: E = (E1E2) MANVE3



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Cc truy vn trn cc mnh hn hp c th c rt gn

bng cch kt hp cc lut s dng trong phn mnhngang nguyn thy, phn mnh dc, phn mnh ngang gintip, tng ng nh sau:

1.Loi b cc quan h rng sinh bi s mu thun gia cc

php chn trn cc phn mnh ngang.

2.Loi b cc quan h v ch sinh bi cc php chiu trn ccphn mnh dc.

3.Phn phi cc php ni vi cc php hp tch v loi bcc php ni v ch.

V d: E1=MANV E4(MANV,TENNV(E)), E2=MANV > E4(MANV,TENNV(E))E3=MANV,CHUCVU(E)


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SELECT TENNVFROM E

WHERE MANV=E5

TENNV

MANV=E5

E2

(b) Truy vn rt gn(a) Truy vn ban u

TENNV

MANV=E5

E1 E2 E3

Hnh 4.11: Rt gn ca phn mnh hn hp


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Distributed Database

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Chuong 6 - Distributed Database