Hi everyone,
I have a trouble understanding one definition of the 5th NF. My professor gave me a chapter about it from a book (I don't know which one is it, it's very old), and the definition of PJNF is as follows:
1. R is in PJNF with respect to F if for every JD *[R1, R2,...Rn] implied by F, every Ri is a superkey for R.
2. Revised definition is: R is in PJNF with respect to F for every JD *[r1,r2..rn] implied by F that applies to R, *[R1, R2, ..., Rn] is implied by the key FDs of R.
if R = A B C and F= { A->BC, C-> AB, *[AB, BC] }
I understand the first, every JD has a superkey in it, but I'm really having trouble grasping the second definition. Could anyone help me and explain why R doesn't meet the second criterion.
Thanks.
I have a trouble understanding one definition of the 5th NF. My professor gave me a chapter about it from a book (I don't know which one is it, it's very old), and the definition of PJNF is as follows:
1. R is in PJNF with respect to F if for every JD *[R1, R2,...Rn] implied by F, every Ri is a superkey for R.
2. Revised definition is: R is in PJNF with respect to F for every JD *[r1,r2..rn] implied by F that applies to R, *[R1, R2, ..., Rn] is implied by the key FDs of R.
if R = A B C and F= { A->BC, C-> AB, *[AB, BC] }
I understand the first, every JD has a superkey in it, but I'm really having trouble grasping the second definition. Could anyone help me and explain why R doesn't meet the second criterion.
Thanks.