CHNG 2: D LIU TRONG H THNG THNG TIN
2.1. Nhng vn chung v c s d liu
2.1.1. D liu v kho d liu
2.1.1.1 Khi nim:
- D liu : Khi ni n d liu l ni nhng s kin bit; chng hn trong c s
d liu (CSDL) v cc cun sch, d liu bao gm cc s kin nh tn sch, nm xut
bn, nh xut bn, hay trong CSDL v s in thoi, gm tn ngi quen, s in
thoi, a ch ca h. Cc d liu tun theo loi d liu c m t trc v c th hin
di dng vn bn, hnh nh, m thanh thm ch c nhng on video. Chng hn CSDL
v th vin c th lu nh ca bn c. D liu l cc s kin, vn bn, ha, hnh nh v
on phim video c ngha trong mi trng ca ngi dng.
- Kho d liu: l kho lu tr d liu lu tr bng thit b in t ca mt t
chc. Cc kho d liu c thit k h tr vic phn tch d liu v lp bo co.
2.1.1.2 Cc mc d liu
Nhng ngi s dng khng phi lun thnh tho v my tnh, v vy cc nh tin hc
phi che du s phc tp v biu din bn trong ca d liu my tnh thng qua
nhiu mc tru tng ho d liu lm n gin ho s tng tc gia ngi s dng v h
thng.
- Mc vt l (physical level): Mc thp nht ca s tru tng ho, m t cch
thc d liu c lu tr thc s.
V d: Cc mu tin c lu thnh nhng khi lin tip nhau (bye, t nh,).
Trnh bin dch che du cc chi tit ny khng cho ngi lp trnh thng thng
bit, tr nhng ngi qun tr CSDL.
- Mc logic (logical level): Mc trung gian, m t nhng d liu no c
lu tr trong CSDL v mi lin kt gia chng. Ngi qun tr CSDL (database
administrator) v cc nh lp trnh thng xuyn lm vic mc ny.
- Mc quan nim (conceptual level) hay con gi l mc khung nhn (view
level): y l mc cao nht ca s tru tng ho. Mc d mc lun l n gin ho i
nhiu nhng do CSDL c kch thc qu ln, n vn cn phc tp. Nhiu ngi s dng
ch cn truy xut mt phn CSDL trong ton b CSDL. V vy khung nhn c t ra
m t ch mt phn ca ton b CSDL cho mt nhm ngi s dng no . Ngoi ra,
khung nhn cn cung cp c ch an ton ngn nga ngi s dng truy xut tri php
cc phn thm quyn.
2.1.2 C s d liu
2.1.2.1 Khi nim
- C s d liu: l tp hp c t chc ca cc d liu v th gii thc trong mt
lnh vc no c lin quan vi nhau v mt logic. Chng c lu tr b nh
ngoi.
Cc c s d liu (CSDL) dng lu tr cc thuc tnh v cc i tng ca th gii
thc, x l v tm kim d liu trong hu ht cc t chc, t kinh doanh, bo him,
gio dc, n th vin, Cng ngh CSDL c th s dng trn my tnh n hoc nhiu my
tnh ni nhau (mng), trong quy m rng ln
2.1.2.2 M hnh c s d liu
Cc m hnh d liu c vai tr quan trng trong vic phn tch v thit k bt
k mt h thng thng tin no. C cc m hnh c s d liu nh sau:
* M hnh lin h thc th
Mc ch ca m hnh thc th lin h l cho php m t lc khi nim ca mt t chc
m khng cn ch n tnh hiu qu hoc thit k CSDL vt l.
Thc th (entity) khng c mt nh ngha hnh thc, cng ging nh cc thut
ng im v ng trong hnh hc ngm c nh ngha bng cc tin v cc c tnh ca
chng. Han tan ni rng : thc th l mt s vt tn ti v phn bit c ngha l c
th phn bit thc th ny vi thc th khc.
Mt nhm bao gm tt c cc thc th tng t nhau to ra mt tp thc th. V d
:
- Tt c mi ngi
- Tt c mi ngi c tc mu
- Tt c mi xe gn my
Mt trong cc bc mu cht chn mt lc cho th gii thc khi n thuc v mt
CSDL c th l chn cc tp thc th, v vy cn m t c im ca tt c cc phn t ca
mt tp thc th bng mt tp cc c tnh gi l thuc tnh, v nh vy tnh tng t t
nht cng i hi tm c mt tp cc c tnh chung cho tt c cc phn t ca mt tp
thc th.
V d :
Phng qun l xe gn my TP. HCM thit k mt lc CSDL c mt tp thc th
XE2BANH. Th hin ca tp thc th l tt c cc xe gn my 2 bnh hin thi c ng
k ti TP. H Ch Minh, ch khng phi tt c cc xe gn my 2 bnh trn th gii
hay cc xe c t trc n gi.
Chn thuc tnh thch hp cho cc tp thc th l mt bc quan trng khc
trong vic thit k lc CSDL khi nim.
Mt thuc tnh hay mt tp cc thuc tnh dng xc nh duy nht mi thc th
trong tp thc th gi l kha i vi tp thc th .
Mi lin h gia cc tp thc th l mt danh sch c th t ca cc tp thc
th.
Mt tp thc th c bit c th xut hin nhiu ln trong danh sch. Danh sch
cc tp thc th ny l khi nim mc lc ca mt mi lin h. Nu c mt mi lin h R
gia cc tp thc th E1, E2, , Ek, th th hin ca R l mt tp cc k-b. Chng
ta gi mt tp nh th l mt tp lin h.
Kha ca tp thc th (Entity Key): l cc thuc tnh nhn din ca loi thc
th. Cn c vo cc gi tr ca cc thuc tnh nhn din ny ngi ta c th xc nh mt
thc th duy nht ca mt loi thc th. V d, kha ca loi thc th LP-HC c th
l M-Lp; kha ca loi thc th HC-VIN c th l M-Hc-Vin; kha ca loi thc th
MN-HC c th l M-Mn-Hc ...
Mi lin h hay kt hp (Entity Relationship): Tng t nh loi mi lin h
trong m hnh d liu mng. Trong th biu din ca m hnh ny ngi ta s dng
hnh thoi th hin mt mi lin h gia cc thc th. Gia 2 tp thc th c th tn
ti nhiu hn mt mi lin h.
m hnh ha y cho th gii thc, cn phi phn loi cc mi lin h theo s lng
cc thc th t mi tp tham gia trong n.
Dng n gin v him gp nht ca mi lin h trn hai tp l mi lin h mt mt,
ngha l i vi mi thc th trong mt tp ch c nhiu nht mt phn t c lin kt
trong tp kia. Ch rng y ch l mt gi thit v th gii thc, v vy ngi thit
k CSDL c th ty chn.
Mi lin h nhiu mt : y mt thc th trong tp E2 c th khng lin kt vi
thc th no hoc lin kt vi mt hay nhiu thc th trong tp E1, nhng mi thc
th trong E1 ch lin kt nhiu nht vi mt thc th trong E2. Mi lin kt ny
c gi l nhiu mt t E1 n E2. Khi nim mi lin h nhiu mt tng qut ha thnh
cc mi lin h gia 3 tp tr ln.
Mi lin h nhiu nhiu : y khng c mt hn ch no trn tp cc k-b ca cc
thc th khi xut hin trong tp lin h. V d mi lin h gia sinh vin v mn
hc : Bi mi mn hc s c nhiu sinh vin ng k hc v mt sinh vin c th ng k
hc nhiu mn. Biu din tnh cht hm trong cc s thc th lin h :
Dng cc cung hay cc cnh c hng c ch ra bi mi tn cho bit, khi no mt
mi lin h l nhiu mt hoc mt mt. Trong trng hp n gin nht, mi lin h
nhiu mt R t A n B, chng ta t mt cung t hnh thoi R n hnh ch nht
B.
V d, gi s mi nhn vin ch c phn cng ti a vo mt phng, iu ny gii
thch mi tn i t PHCONG n PHONG:
Nu R l mi lin h mt mt gia A v B chng ta v mt mi tn t R n c A v
B. V d : cc trng phng ch qun l mt phng, v cc phng ch c 1 trng
phng.
* M hnh d liu mng
M hnh d liu mng (Network Data Model) - cn c gi tt l m hnh mng
hoc m hnh li (Network Model) l m hnh c biu din bi mt th c hng.
Trong m hnh ny ngi ta a vo cc khi nim: mu tin hay bn ghi (Record),
loi mu tin (Record Type) v loi lin h (Set Type): - Loi mu tin
(Recorde Type) l mu c trng cho 1 loi i tng ring bit. Chng hn nh
trong vic qun l nhn s ti mt n v, i tng cn phn nh ca th gii thc c th
l Phng, Nhn vin, Cng vic, l lch ... do c cc loi mu tin c trng cho
tng i tng ny. Trong th biu din m hnh mng mi loi mu tin c biu din bi
mt hnh ch nht, mt th hin (Instance) ca mt loi mu tin c gi l bn ghi.
Trong v d trn loi mu tin Phng c cc mu tin l cc phng, ban trong n v;
loi mu tin nhn vin c cc mu tin l cc nhn vin ang lm vic ti cc phng
ban ca c quan...- Loi lin h (Set Type) l s lin kt gia mt loi mu tin
ch vi mt loi mu tin thnh vin. Trong th biu din m hnh mng mi loi lin
h c biu din bi mt hnh bu dc (oval) v s lin kt gia 2 loi mu tin c th
hin bi cc cung c hng (cc mi tn) i t loi mu tin ch ti loi lin h v t
loi lin h ti loi mu tin thnh vin. Trong loi lin kt ngi ta cn ch ra
s lng cc mu tin tham gia trong mi kt hp. C cc loi lin h sau:
1 - 1 (One-to-One): Mi mu tin ca loi mu tin ch chi kt hp vi ng 1
mu tin ca loi mu tin thnh vin. V d, mi nhn vin c duy nht mt l lch c
nhn.
1 - n (One-to-Many): Mi mu tin ca loi mu tin ch chi kt hp vi 1
hay nhiu mu tin ca loi mu tin thnh vin. V d, mi phng ban c t 1 n
nhiu nhn vin. Mi 1 nhn vin ch thuc mt phng ban nht nh.
n - 1 (Many-to-One): Nhiu mu tin ca loi mu tin ch ch kt hp vi ng
1 mu tin ca loi mu tin thnh vin. V d, nhiu nhn vin cng lm mt cng
vic.
quy (Recursive): Mt loi mu tin ch cng c th ng thi l loi mu tin
thnh vin vi chnh n. Ta ni rng loi lin h ny l quy.
V d v m hnh d liu mng i vi CSDL nhn s ca mt n v.
Trong th ny, chng ta c 4 loi mu tin: PHNG, NHN-VIN, CNG-VIC v
L-LCH;
4 loi lin h:
Phng gm 1 n nhiu nhn vin;
Nhn vin c ng 1 l lch;
Nhiu nhn vin cng lm mt cng-vic;
- 1 nhn vin c th c 1 hay nhiu nhn vin l thn nhn ca mnh.
* M hnh d liu phn cp
M hnh d liu phn cp (Hierachical Data Model) - c gi tt l m hnh
phn cp (Hierachical Model): M hnh l mt cy (Tree), trong mi nt ca cy
biu din mt thc th, gia nt con v nt cha c lin h vi nhau theo mt mi
quan h xc nh.
M hnh d liu phn cp s dng cc khi nim sau:
Loi mu tin: ging khi nim mu tin trong m hnh d liu mng.
Loi mi lin h: Kiu lin h l phn cp, theo cch:
+ Mu tin thnh vin ch ng vai tr thnh vin ca mt mi lin h duy nht,
tc l n thuc mt ch duy nht. Nh vy, mi lin h t mu tin ch ti cc mu tin
thnh vin l 1n, v t mu tin (hay bn ghi - record) thnh vin vi mu tin
ch l 11.
+ Gia 2 loi mu tin ch tn ti 1 mi lin h duy nht.
V d Mu phiu iu tra dn s
Cc dng l cc mu tin (hay bn ghi) c di thay i.
C 6 loi mu tin:
+ Mu tin c trng cho tnh, thnh ph gm M s tnh thnh, Tn tnh thnh
ph.
'02' l M s Thnh ph H Ch Minh.
+ Mu tin c trng cho qun huyn gm M s tnh thnh + M s qun huyn, Tn
qun huyn trong tnh thnh ph . '0201' l M s qun Nht ca TP.H Ch
Minh.
+ Mu tin c trng cho phng x gm M s tnh thnh + M s qun huyn + M s
phng x, Tn phng x thuc qun huyn trong tnh thnh ph . '020101' l M s
phng Bn Ngh, Qun Nht, TP.H Ch Minh.
+ Mu tin c trng cho a bn iu tra trong mt phng x. '02010101' l m
s a bn iu tra s 01 trong phng Bn Ngh.
+Mu tin c trng cho h iu tra, gm M s tnh + M s qun + M s phng + M
s a bn + S th t h iu tra trong a bn, Tng s nhn khu trong h, Trong :
N, Tng s tr di 16 tui.
+ Mu tin c trng cho nhn khu ca h, gm cc thng tin xc nh h iu tra,
S th t nhn khu trong h, Quan h vi ch h (19), Gii tnh (1,2,3), Thng
sinh, Nm sinh, Trnh vn ha, ...
y r rng l mt s phn cp trong file CSDL.
Mt tnh thnh ph (th) c nhiu qun huyn, mt qun huyn ch thuc mt tnh
thnh duy nht. Mt qun huyn (th) c nhiu phng x v mt phng x ch thuc mt
qun huyn duy nht. Mi phng x c chia thnh nhiu a bn iu tra, mi a bn
ch thuc mt phng x duy nht v.v... * M hnh hng i tng
M hnh d liu hng i tng (Object Oriented Data Model) ra i t cui
nhng nm 80 v u nhng nm 90. y l loi m hnh tin tin nht hin nay da trn
cch tip cn hng i tng quen thuc trong cc phng php lp trnh hng i tng,
n s dng cc khi nim nh lp (class), s k tha (inheritance), k tha bi
(tc l kt tha t nhiu lp c s multi-inheritance). c trng c bn ca cch
tip cn ny l tnh ng gi (encapsulation), tnh a hnh (polymorphism) v
tnh ti s dng (Reusability).
- Lp (class) l mt kiu d liu c cu trc bao gm cc thnh phn d liu v
cc phng thc x l thao tc trn cu trc d liu . N l mt kiu (hay cu trc)
d liu c tru tng ha, bi v cc tc ng (cn gi l cc phng thc - method) l
phc v hoc thao tc trn kiu d liu ny.
D liu v phng thc ha quyn vo nhau thnh mt th thng nht: d liu cn c
nhng cch thc x l tha ng, v phng thc x l c a vo trong kiu d liu l
phc v cho cc i tng c cu trc nh th. Ngi ta gi s thng nht l s ng
gi.
Phng php tip cn hng i tng trong m hnh d liu mc d cn mi m nhng
hin nay ang c nhiu ngi quan tm nghin cu pht trin v p dng. Cc h qun
tr CSDL hng i tng hin nay vn cha nhiu, mt s cn cha thun nht (ngha l
vic lp trnh l hng i tng nhng CSDL vn ch yu da trn m hnh quan
h).
2.1.2.3 Li ch v hn ch khi s dng CSDL
* Li ch:
- Gim bt d tha d liu: Khi c hai h ng dng khc nhau cng i hi nhng
tp d liu nh nhau th ch lu tr mt ln v dng chung cho c hai h ni trn.
Tuy nhin vic d tha d liu khng th ht c; chng hn nh cc d liu lin kt
cc tp tin d liu khc nhau vn c lu tr trn nhiu tp tin.
- C th trnh c s khng nht qun trong d liu lu tr: Nu d liu lu tr
nhiu ni khc nhau th c th khng nht qun do nhng thao tc cp nht. y
CSDL gim c d tha th kh nng ri ro do thay i gi tr cng gim i.
- Tng tnh dng chung d liu: Mt CSDL c thit k phc v chung cho tt c
cc ng dng. Mi nhm ngi dng nhn nhn CSDL nh ch c mt mnh h s dng d
liu.
- Tnh chun ho cao: Khi d liu c s dng trong nhiu lnh vc th chng
cng ngy cng c chun ho cho ph hp vi nhiu nhu cu; vic theo chun chung
cho php tng hiu qu s dng d liu.
- Tng tnh an ton d liu: Ngi qun tr CSDL c th cho php mt nhm ngi
s dng no s dng ch mt nhm d liu thuc thm quyn, bng mt mt m c nh trc.
ng thi cng c th kim tra cc truy xut n d liu mt.
- C th gi c s ton vn d liu: CSDL ch c cha cc d liu ng. Nh s qun
l tp trung, n cho php ngi qun tr nh ra cc th tc kim tra cn thit khi
thc hin cc thao tc cp nht.
V d: S lng hng bn khng th vt qu s lng hng ang tn.
- C th m bo tnh c lp d liu cao. - Gim bt vic bo tr cc chng
trnh.
* Hn ch: Nh vi bt k quyt nh kinh doanh no, ng dng theo hng CSDL
cn tr gi v chu mt vi ri ro nh cn n nhn s mi v chuyn su, chi ph qun
l v thc hin, gii quyt va chm tm l
- Nhu cu v nhn s mi, chuyn mn: Cn phi thu hay t o to cc chuyn
gia cng ngh thng tin phn tch, thit k, thc hin CSDL trong t chc. Mc
khc cng ngh ngy cng pht trin nhanh khin cc h thng CSDL thng xuyn cp
nht tri thc cho cc cn b.
- Chi ph v qun l, thc hin: H thng qun tr CSDL nhiu ngi dng thng
ln v phc tp, i hi nhiu ngi tham gia v bo tr. Ngi ta cn tnh n chi ph
thit b my tnh, chi ph phn mm, chi ph truyn thng.
- Chi ph chuyn i h thng: Trc khi p dng CSDL, t chc x l d liu
theo phng php th cng, hay s dng h thng x l tp. chuyn cng ngh x l d
liu sang cch tip cn mi, t chc cn c kinh ph chuyn cc m hnh c sang m
hnh mi, chuyn i d liu cho ph hp vi mi trng mi.
- Nhu cu sao chp v khi phc d liu: Tuy khng mong mun, nhng i khi
vn xy ra ri ro vi CSDL nh mt d liu, hng phn mm, hng phn cng,H thng
CSDL c cc cng c cho php sao chp d liu phng khi hng hc v khi phc li
d liu khi xy ra s c.
- Va chm v quan im s dng CSDL: Trc khi CSDL c p dng trong t chc,
ngi ta cn thng nht v m t d liu, cc khun dng th hin d liu, Sau khi
hnh thnh CSDL, vic s dng d liu ca CSDL cn t hiu qu. Cn khuyn khch
cc b phn pht huy tt h thng CSDL v rt c th mt s b phn no mun c quyn
thng tin hay e ngi dng h thng t ng ho, cho nn c xu hng gim hiu qu
ca CSDL.
2.3. C s d liu trong h thng thng tin k ton
2.3.1 Cc thnh phn d liu
xy dng mt c s d liu cho h thng thng tin k ton, ta phi thu thp cc
d liu vi cc ni dung nh sau:
Hot ng: Cc ni dung thc heiejn trong cc qu trnh trao i ngun lc ca
qu trnh SXKD.
+ Hot ng xt duyt: Cho php qu trnh trao i c thc hin.
+ Hot ng thc hin: Thc hin trao i ngun lc.
+ Hot ng ghi nhn, theo di: Ghi nhn ni dung trao i ngun lc.
Ngun lc: Cc ngun lc kinh t lin quan n qu trnh trao i.
i tng: C nhn, b phn lin quan cn theo di cho qu trnh trao i.
Ni dung ca m hnh thu thp d liu trn c minh ho theo hnh sau:
Cc thnh phn d liu c th c thu thp trong h thng thng tin k ton bao
gm:
Chng t: Thu thp cc ni dung (d liu) ca cc hot ng thc hin qu trnh
trao i ngun lc.
Ti khon: Thu thp cc ni dung ca cc ngun lc pht sinh trong qu trnh
trao i cc ngun lc theo yu cu thng tin trn bo co ti chnh v thng tin
qun l.
i tng chi tit: Thu thp cc ni dung ca cc ngun lc, i tng cn theo
di trong qu trnh trao i cc ngun lc theo yu cu thng tin qun l.
2.3.2 T chc c s d liuTrong h thng thng tin k ton, c s d liu l tt
c cc d liu c lu tr v c s dng bi doanh nghip to thnh. C s d liu ca
doanh ngip c t chc di hai dng c bn l: T chc d liu th cng bng tay v
t chc c s d liu bng my vi tr gip ca my tnh cng nh cc h qun tr c s d
liu.
D c t chc theo dng no, d liu cng s c t chc di dng logic theo m
hnh sau:
V d: Di y y l mt v d v t chc logic tp tin d liu v khch hng trong
h thng thng tin k ton:
Cc loi tp tin lu tr d liu:
C hai loi tp tin dng lu tr d liu trong h thng thng tin k
ton:
Tp tin chnh (Master File): Lu tr cc d liu t thay i v i tng trong
v ngoi h thng. VD: Khch hng, Hng ho.....
+ Tp tin chnh khng cha cc d liu v cc s kin pht sinh.
+ Cc d liu lu tr c th l cc d liu tham chiu hay d liu
VD:
tng hp.
Tp tin nghip v (Transaction File): Lu tr d liu v cc s kin: t
hng, bn hng, thu tin,...
+ Lun cha cc trng ngy ca s kin v nghip v.
+ Lun cha cc d liu v gi c, s lng lin quan n s kin.
VD:
Li ch ca tp tin chnh v tp tin nghip v: Gim thi gian nhp liu
Trnh lu tr trng lp d liu.
Tng cng kh nng kim sot d liu.
Thun tin trong vic bo qun d liu.
Thun tin cho cc hot ng kim sot d liu.
2.3.2.1 T chc cc hot ng ghi nhn d liu
Cc hot ng ghi nhn d liu bao gm:
Nhp liu, ghi nht k (recording): Nhp cc s kin pht sinh theo thi
gian vo h thng.
Cp nht, chuyn s (update): Tc ng thay i cc s liu lu tr (s d TK, s
d chi tit KH...) sau khi s kin xy ra.
Bo tr v khai bo: m bo duy tr cc d liu v cc i tng thng s dng
(Khch hng, nh cung cp, ti khon, nhn vin,...)
- Trong m hnh th cng, cc hot ng ghi nhn d liu s c t chc theo bn
hnh thc ghi s th cng nh m hnh sau:
Trong h thng thng tin k ton trn nn my tnh, cc hot ng ghi nhn d
liu c t chc theo m hnh sau:
2.3.2.2 So snh t chc d liu th cng v my tnh:
Hai hnh thc t chc d liu k ton theo th cng v bng my tnh thc cht
ch khc nhau v phng thc t chc tp tin trong c s d liu.
V d: Ngy 2/1/20X1, cng ty k hp ng s 01 bn chu cho khch hng A 300
kg hng ho CC, vi s tin 10 triu ng. Ngy 4/1/20X1, cng ty thc hin hp
ng v pht hnh ho n s 35 gi n khch hng A.
Vi v d trn, nu d liu c t chc th cng th s nh sau:
Tuy nhin nu c t chc vi h thng my tnh, d liu s c t chc nh
sau:
Qua v d trn ta c th so snh hai phng thc t chc d liu h thng thng
tin k ton qua bng cc tiu ch sau:
Th cngMy tnh
Hot ng Lu trHot ng Lu tr
Ghi nht k -> S nht kNhp liu -> Tp tin nghip v
Khai bo -> Tp tin chnh
Chuyn s -> S ci, s chi titCp nht -> Tp tin chnh
Thng tin cung cp chmThng tin cung cp nhanh chng
