Domain-Key Normal Form (DKNF) Designed to specify the “ultimate normal form” which uses all possible types of dependencies and constraints. A relation is in DKNF if all constraints and dependencies on the relation can be enforced by enforcing the domain constraints and key constraints on the relation. The practical utility of DKNF is limited, because it is difficult to specify general integrity constraints. It has been shown that a relation in DKNF is in 5NF and that DKNF is not always achievable. Example of relations with complex constraints:CAR = {MAKE, VIN#}, MANUFACTURE = {VIN#, COUNTRY} where COUNTRY is the country where the car was manufactured. A complex constraint isFor a Toyota or Lexus made in Japan, the first character of the VIN# is a “J”; for a Honda or Acura made in Japan, the second character of the VIN# is a “J”. Example: R = {BRANCH, ACCTNUM, BALANCE}Constraint: An ACCTNUM beginning with 9 is a special account which requires a minimum balance of $2,500.R is not in DKNF. Replace R by the decomposition D = {R1, R2} where R1 = {BRANCH, ACCTNUM, BALANCE} with the constraint that an ACCTNUM does not begin with 9 and R2 = {BRANCH, ACCTNUM, BALANCE} with the constraints that an ACCTNUM begins with 9 and the BALANCE is greater than or equal to 2500. D is in DKNF.
不过我们一般使用的表都不会高于3NF,只有个别的是BCNF,
更不用说4NF \5NF \DKNF了，这些东西一般只存在于论文中：）在工程中使用较低级的范式是一种空间换速度的好方法。
如果你想了解的话，随便找一本经典数据库教材，里边都有讲述。
account which requires a minimum balance of $2,500.R is not in DKNF. Replace R by the decomposition D = {R1, R2} where R1 = {BRANCH, ACCTNUM, BALANCE} with the constraint that an ACCTNUM does not begin with 9 and R2 = {BRANCH, ACCTNUM, BALANCE} with the constraints that an ACCTNUM begins with 9 and the BALANCE is greater than or equal to 2500. D is in DKNF.