Zomwe Zimagwira Ntchito Zomwe Zimagwiritsidwa Ntchito M'zinenero Zambiri

Kudalira kwathunthu kumagwiridwe ndi machitidwe omwe amafanana ndi a normalization of Form Formal Second Form (2NF) . Mwachidule, izi zikutanthauza kuti zimakwaniritsa zofunikira za Fomu Yoyamba Yoyamba (1NF), ndipo zonse zomwe sizinthu zofunikira zimadalira kotheratu pachifungulo chachikulu.

Izi sizili zovuta monga zingamveka. Tiyeni tione izi mwatsatanetsatane.

Chidule cha Fomu Yoyamba Yoyamba

Pambuyo pa malo osungirako deta akhoza kukhala wodalirika mokwanira, ayenera kuyamba choyamba ndi Fomu Yoyamba Yoyamba .

Zonsezi zikutanthauza kuti malingaliro onse ayenera kukhala ndi mtengo umodzi, wa atomiki.

Mwachitsanzo, tebulo lotsatira silikugwirizana ndi 1NF, chifukwa wogwira ntchito Tina akugwirizanitsidwa ndi malo awiri, onse awiri mu selo limodzi:

Kulolera kuti mapangidwe awa akhoza kuthandizira kwambiri kusintha kwa deta kapena zolembera. Kuti muonetsetse kuti mukutsatira 1NF, konzekerani tebulo kuti zonse (kapena maselo a maselo) akhale ndi mtengo umodzi:

Koma 1NF akadakalibe kupeŵa mavuto ndi deta.

Momwe 2NF imathandizira kuti mukhale otsimikizirika

Kukhala wodalirika kwathunthu, malingaliro onse omwe sali ovomerezeka ayenera kudalira pachinsinsi chachikulu. (Kumbukirani, chinthu chofunika kwambiri ndichinsinsi (mwachitsanzo, choyimira chachikulu kapena chachilendo) chomwe chimagwiritsidwa ntchito podziŵika bwino mbiri yachinsinsi.

Anthu ogwiritsa ntchito malowa amagwiritsira ntchito ndondomeko kuti afotokoze ubale wodalirika pakati pa zikhumbo:

Ngati chidziwitso A chimayesa ubwino wa B, timalemba izi A -> B - kutanthawuza kuti B imadalira kwambiri A. Mu ubale umenewu, A amadziwa kufunika kwa B, pamene B ikudalira A.

Mwachitsanzo, m'tawuni yotsatila antchito, EmployeIDID ndi DeptID ndizo mafungulo onse oyenera: Ogwira ntchito ndiye galasi lofunika kwambiri pamene DeptID ndichinsinsi chachilendo.

Chidziwitso china chilichonse - pa ntchitoyi, EmployeeName ndi DeptName - chiyenera kudalira chimfungulo chachikulu kuti chipeze phindu lake.

Pankhaniyi, tebulo silidalira kwambiri chifukwa, pamene EmployeeName imadalira ntchito yaikulu ya EmployeeID, DeptName imadalira pa DeptID. Izi zimatchedwa kudalira kwathunthu .

Kuti pangani tebulo ili likhale lofanana ndi 2NF, tifunika kulekanitsa deta mu magome awiri:

Timachotsa chidziwitso cha DeptName ku gome la antchito ndikupanga magalimoto atsopano:

Tsopano mgwirizano pakati pa magomewo umadalira kwathunthu, kapena 2NF.

Chifukwa Chake Kudalira Kwambiri N'kofunika

Kugonjera kwathunthu pakati pa zida za databases kumathandiza kutsimikizira kukhulupirika kwa deta ndikupewa zolakwika za deta.

Mwachitsanzo, taganizirani tebulo mugawo lomwe lili pamwambapa limene limatsatira 1NF yokha. Ndi izi apa, kachiwiri:

Tina ali ndi zolemba ziwiri. Ngati tikusintha imodzi popanda kuzindikira kuti pali ziwiri, zotsatira zake zikanakhala deta yosagwirizana.

Kapena, nanga bwanji ngati tikufuna kuwonjezera wogwira ntchito patebulo lino, koma sitikudziwa malowa? Tikhoza kuvomerezedwa ngakhale kuwonjezera antchito atsopano ngati chiwonetsero cha malo sichilola miyezo ya NULL.

Kudalira kwathunthu sizithunzi zonse, komabe, pankhani ya normalization. Muyenera kuonetsetsa kuti malo anu otchulidwa m'ndandanda ali mu Fomu Yachiwiri (3NF).