The relationship set R with descriptive attributes r1, r2, ..., rn, relating entity set A on the 1 end to entity set B on the other 1 end, is normally not converted into a relation of its own. Instead, the relationship is realized either by moving the primary key of A into B, together with all the attributes of R or, vice versa, by moving the primary key of B into A, together with all the attributes of R. Supposing {b1} is the primary key of B and the second option is chosen, then the schema definition would be
A = ( a1(PK), ..., an, r1, ..., rn, b1(FK) )
Notice how the relational model's representation of 1:1 relationship sets is functionally the same as that of 1:N relationship sets. Refer to the Integrity Constraints chapter to see how the distinction can be imposed and how total participation is realized.