BCNF in DBMS

What is BCNF?

3NF vs BCNF

Every BCNF table is in 3NF, but not every 3NF table is in BCNF. BCNF removes anomalies that 3NF can still leave when there are multiple overlapping candidate keys.

Example

Table (student, subject, teacher) where each teacher teaches one subject. Here teacher → subject but teacher is not a candidate key — so it violates BCNF. Split into (student, teacher) and (teacher, subject).

Summary

• BCNF: for every dependency X → Y, X must be a candidate key.
• Stricter than 3NF; removes anomalies from overlapping candidate keys.

BCNF क्या है?

3NF बनाम BCNF

हर BCNF table 3NF में है, पर हर 3NF table BCNF में नहीं। BCNF उन anomalies को हटाता है जो overlapping candidate keys होने पर 3NF में भी रह सकती हैं।

Example

Table (student, subject, teacher) जहाँ हर teacher एक subject पढ़ाता है। यहाँ teacher → subject पर teacher candidate key नहीं — तो BCNF violate होता है। (student, teacher) और (teacher, subject) में split करें।

सारांश

• BCNF: हर dependency X → Y के लिए X candidate key हो।
• 3NF से सख्त; overlapping candidate keys की anomalies हटाता है।