Research on Relational Schema Decomposition Under Null Value Circumstances

On the basis of literatures 1 2 3,the problem of incomplete relational schema decompositions is discussed.Since incomplete relations contain many kinds of functional dependency holds,these kinds of functional dependency holds cause the dependent relations among attributes in incomplete relations to be complicated and have dynamic properties.Therefore a new decomposi- tion theory and method should be given in schema decomposition in order to solve the problems bring- ing from null values.So the problems of candidate keys,projection and join under null value circ- umstances are discussed in this paper.And the method to decomposit incomplete relational schema con- taining definite candidate keys into 2NF with null values with lcssless joins and its decision algorithm are proposed.