The relationship set R with descriptive attributes r1, r2, ..., rn, relating entity set A and entity set B with a cardinality of N on both ends, is always converted into a relation of the same name R with n distinct attributes, each of which corresponds to an attribute of the relationship set, plus the attributes, that form the primary key of A and the primary key of B. The primary key of the derived relation will be formed by the combination of the primary keys of the relations involved in the relationship. Moreover, the attributes, that form the primary key of the derived relation, will also have to be indicated as foreign keys in the schema definition, as they refer to “foreign” relations
R = ( a1(PK)(FK), b1(PK)(FK), r1, r2, ..., rn )
Notice that N:N relationship sets may have a degree greater then 2 (the degree of a relationship set is the number of participating entity sets).