Kedu Ụdị Ụdị Ụdị Ụdị (Cdd Normal Form (BCNF)?

BCNF na - ebelata redundancies ma na - eme ka njikarị data dị

Ihe mgbaru ọsọ nke Boyce-Codd Normal Form (BCNF) bụ ịbawanye njikwa data site na ịhazi ogidi na tebụl nke data nchekwa data iji nweta nhazi data nchekwa. Usoro nhazi data na- eme mgbe enwere mmekọrịta dị n'etiti tebụl na mgbe tebụl kọwaa iwu iji mee ka nchekwa data gbanwee ma chebe data.

Ihe mgbaru ọsọ nke normalization data bụ iji kpochapụ data redundant na iji hụ na ịdabere na data nwere uche.

A na-edozi nchekwa data mgbe anaghi echekwa data a karịa otu tebụl na mgbe naanị data metụtara dị na tebụl.

Mmalite nke Boyce-Codd Normal Form

Ịgbaso usoro ntụziaka ga-eme ka ịchọta data ịntanetị. A na-akpọ ụkpụrụ nduzi ndị a dị ka ụdị nkịtị ma na-agụnye site na otu n'ime ise. A na-akọwa nchekwa data na-eme ka ọ bụrụ nke ọma ma ọ bụrụ na ọ na-ezute ụdị atọ mbụ: 1NF, 2NF, na 3NF.

E mere DNNF dị ka mgbatị na ụdị nke atọ, ma ọ bụ 3NF, na 1974 site n'aka Raymond Boyce na Edgar Codd. Ndị ikom ahụ na-arụ ọrụ iji mepụta nkesa nchekwa data nke na-eme ka redundancies dị ntakịrị na mgbaru ọsọ iwelata oge nhazi. Ụdị nkeji nke atọ na-ewepu ogidi ndị na-adabere na isi isi na mgbakwunye na ịgbaso ntụziaka na ụdị nke mbụ na nke abụọ. BCNF, nke a na-akpọkarị 3.5NF, na-eme ihe niile chọrọ 3NF ma na-achọ ka igodo ndị ọrụ ahụ ghara ịdabere na àgwà ndị ọzọ na tebụl.

N'oge BCNF kere, Boyce bụ otu n'ime ndị mmepe nke Structured English Query Language (SQL), nke nweliteghachi data site na iji usoro mmekọrịta nke Codd. N'ihe atụ a, Codd kwadoro na mgbagwoju anya nke ọdụ data nwere ike belata, nke pụtara na ajụjụ nwere ike ịdị ike ma gbanwee.

N'iji ihe omuma nchekwa data ya, Codd kọwara 1NF, 2NF, na 3NF ntụziaka. O sooro Boyce kwupụta BCNF.

Okpukpe ndị Candidate na BCNF

Otu igodo ndi choro bu udi ma obu nchikota nke akwukwo na tebulu nke puru isi na nchekwa data. Njikọ nke njirimara nwere ike iji mee ka ihe ndekọ nchekwa data chọpụta ihe ọ bụla data. Tebulu ọ bụla nwere ike ịnwe ọtụtụ igodo ndị ntinye, nke ọ bụla n'ime ha nwere ike iru eru dị ka isi ihe dị mkpa. Otu tebụl nwere naanị isi isi.

Igodo igodo kwesịrị ịbụ ihe pụrụ iche.

Otu mmekọrịta dị na BCNF ọ bụrụ na onye ọ bụla kpebiri bụ isi ihe ntinye. Tụlee table nke nchekwa data na-echekwa ozi ndị ọrụ ma nwee àgwà , , , na .

Na tebụl a, ubi na-ekpebi aha mbido na aha ikpeazụ. N'otu aka ahụ, tuple (, ) na-ahọpụta .

Ihe ntinye akwukwo maka nchekwa data a bu n'ihi na obu nani uru nke enweghi ike iji ya.