Wat ass Boyce-Codd Normal Form (BCNF)?

by Mike Chapple

BCNF miniméiert Reduktiounen an erhéit d'Integritéit vu Daten

D'Zil vum Boyce-Codd Normal Form (BCNF) ass fir d' Integritéit vun Daten ze vergréisseren an d'Säiten a Tabellen vun enger relationaler Datenbank ze organiséieren fir d'Standardiséierung vun der Datebank z'erreechen. D'Normaliséierung vun der Database trëfft wann et Bezéiungen tëschent Dëschen gefall sinn a wann d'Tabellen Regelen definéiert hunn fir d'Datebank méi flexibel ze maachen an d'Daten ze konservéieren.

D'Ziler vun der Datebanknormaliséierung sollen d'Redundante Donnéeën eliminéieren an fir d'Ofhängegkeet vu Daten ze suergen.

Eng Datebank normaliséiert wann déi selwecht Daten net a méi wéi enger Tabelle gelagert sinn an wann nëmmen verwandte Donnéeën an enger Tabelle gelagert sinn.

Ursprénglech vun Boyce-Codd Normal Form

No enger Rei vu Richtlinne suergen datt Datenbanken normaliséiert ginn. Dës Richtlinne ginn normalt Formen bezeechent an nummeréiert vun enger vun fënnef. Eng relational Datenbank gëtt norméierend bezeechent, wann et den éischten dräi Formen entsprécht: 1NF, 2NF a 3NF.

BCNF gouf als Ausdehnung vun der drëtter normaler Form oder 3NF, 1974 vun Raymond Boyce an Edgar Codd geschaf. D'Männer hu missen Aarbechtsplazen schafen, déi Reduktiounen mat dem Ziel fir d'Zäit ze reduzéieren. Déi drëtt normale Form remt Spalten, déi net vun der Primärschreiwe sinn abegraff fir d'Richtlinnen an der éischter an zweeter normaler Form ze treffen. BCNF, deen heiansdo 3.5NF bezeechent gëtt, entsprécht all de Viraussetzungen vun 3NF a verlaangt datt Kandidaten keng Abhängie vu aner Attributer an engem Dësch hunn.

Zu der Zäit vun der Grënnung vun der BCNF ass de Boyce eng vun den Haaptentwéckler vun der Strukturéierter englescher Query Language (SQL), déi d'Datebezuche mat Hëllef vu Relatiounsmodul Codd verbessert huet. An dësem Modell huet Codd de strukturelle Komplexitéit vu Datenbanken reduzéiert, wat Ufroen misst méi staark a flexibel sinn.

Mat senger relationaler Datebankinnentitele benotzt Codd definéiert 1NF, 2NF a 3NF Richtlinnen. Hien huet mat Boyce mat der BCNF definéiert.

Kandidat Keys a BCNF

E Kandidatschloss ass eng Kolonn oder eng Kombinatioun vun Spalten an enger Tabell déi e unique e Schlëssel an der Datebank bildet. D'Kombinatioun vun Attributer kann benotzt ginn fir e Datebank ze identifizéieren ouni datt aner aner Donnéeën. Jiddfer Tafel kann méi Kandidaten, an deenen een als Primärschlass qualifizéiert ka sinn. Eng Tabelle enthält nëmmen een éischte Grondschlag.

Kandidatentschlüser mussen eegent ginn.

Eng Relatioun ass an der BCNF wann all Determinante e Kandidatschloss ass. Bedenkt eng Datebankstabelle déi Mataarbechterinformatioune späichert an huet déi Attributer , , , an . </p> <p> An dëser Tafel ass de Feld <Employee_Id> den éischte Numm an d'lescht_Name. Andeems de Tupel (<First_name>, <Last_Name>) bestëmmen <Employee_id>. </p> <table><tbody><tr><td> <strong>Employé Id</strong> </td><td> <strong>Virnumm</strong> </td><td> <strong>Familljennumm</strong> </td><td> <strong>Titelen</strong> </td></tr><tr><td> 13133 </td><td> Emily </td><td> Smith </td><td> Manager </td></tr><tr><td> 13134 </td><td> Jim </td><td> Smith </td><td> Associate </td></tr><tr><td> 13135 </td><td> Emily </td><td> Jones </td><td> Associate </td></tr></tbody></table><p><br> De Kandidatschléier fir dës <a href="https://lb.eyewated.com/glossary-vun-der-gemeinsamer-datenbank-bedengungen/">Datebank</a> ass de <Employee_Id>, well et ass deen eenzegen Wäert deen net vun enger anerer Zeil benotzt ka ginn. </p> </div> <div class="amp-related-wrapper"> <h2>Alike posts</h2> <div class="amp-related-content"> <a href="https://lb.eyewated.com/microsoft-access-2007-books-for-beginners/"> <amp-img src="https://exse.eyewated.com/pict/734f7bd077372f3a-120x86.jpg" width="120" 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