1nf-> 2nf: removes some function dependencies of non-primary attributes on codes.
2nf-> 3nf: removes the function dependency on code passing by non-primary attributes
3nf-> bcnf: removes the part and function dependency of the primary attribute on the code. Example: The following dependencies are full function dependencies:
(SNO, CNO)-> grade
Sno-> sdept
Sdept-> sloc
(SNO, CNO)-> teacher
(SNO, teacher)-> CNO
Teacher-> CNO Sno: Student No. CNO: course No. sdept: department sloc: Address Teacher: Instructor 2nf:
S-L-C (SNO, sdept, sloc, CNO, grade)
Master code: (SNO, CNO), the above mode does not meet 2nf, can be split as follows:
(SNO, CNO, grade) (SNO, sdept, sloc) 3nf:
S-D-C (SNO, sdept, sloc)
Primary code: SnO
The above mode does not meet 3nf. You can split it as follows:
(SNO, sdept) (sdept, sloc) Bcnf:
SCT (SNO, CNO, teacher)
Candidate Code: (SNO, teacher), (SNO, CNO)
If the above mode does not meet bcnf, you can split it as follows:
(SNO, teacher)
(Teacher, CNO) |
