Ngokwexhomekeke komsebenzi ongenamsebenzi omnye umxholo wesinye
Kwihlabathi le-theory ye-database, ukuxhomekeka komsebenzi kukhona xa enye impawu ibeka enye into ebonakalayo kwi-database. Ukuxhomekeka kokusebenza okungafaniyo kukuxhomekeka kwenkcukacha ezikhoyo xa kuchaza ukuxhomekeka kokusebenza kombono okanye ukuqokelela kweempawu ezibandakanya umlingiso wokuqala.
Imizekelo yokuxhomekeka kokuSebenzayo okungekho
Olu hlobo lokuxhomekeka lubizwa ngokuba luyingcipheko ngenxa yokuba lunokuvela kwisimo esivakalayo. Ukuba elinye "icala" lincinane yesinye, kuthathwa njengento encinci. Icala lasekhohlo libhekwa njengelisigxina kunye nelungelo elixhomekeke kulo .
- {A, B} -> B kukuxhomekeka kokusebenza okuncinci ngenxa yokuba uB i-subset ye- A, B. Ekubeni { A, B} -> B iquka iB , ixabiso leB liyakunikwa. Ukuxhomekeka okuyingcosana kokusebenza ngenxa yokuba u-B unelisekile ngolwalamano lwawo no-A, B. Ekubeni iinqununu ze- B zichongiwe ziimpawu ze- A , nayiphi na enye ilandelelwano ekwabelana ngexabiso le- A iya kuba nexabiso elifanayo njengeB . Enye indlela yokuyibeka kukuba yonke iB ibandakanywe kwi- A , yintoni eyenza i - subset.
- {Employee_ID, Employee_Name} -> U-Employee_ID uphinde uxhomekeke kumsebenzi osebenzayo ukususela ngo- Employee_ID kukusetyenzana {Employee_ID, Employee_Name} .
- Kuyafana ne- A -> A okanye i- Employee_ID -> Employee_ID, kunye ne- Employee_Name-> Employee_Name . Ezi zizo zonke izinto ezincinci ezixhomekeke kuzo.
- Ukuba ukuxhomekeka komsebenzi X-> Y, kunye neY kuyinxalenye yesigxina se-X, oku kukuxhomekeke kumsebenzi ongenanto. Ukuba i-Y ayilona i-subset ye-X, oku akusiko kuxhomekeke kumsebenzi ongenanto.