Consider a many-to-one relationship set AB from entity set A to entity set B. Using
our table-construction scheme outlined previously, we get three tables: A, B, and AB.
Suppose further that the participation of A in the relationship is total; that is, every
entity a in the entity set A must participate in the relationship AB. Then we can
combine the tables A and AB to form a single table consisting of the union of columns
of both tables.
As an illustration, consider the E-R diagram of Figure 2.27. The double line in the
E-R diagram indicates that the participation of account in the account-branch is total.
Hence, an account cannot exist without being associated with a particular branch.
Further, the relationship set account-branch is many to one from account to branch.
Therefore, we can combine the table for account-branch with the table for account and
require only the following two tables:
• account, with attributes account-number, balance, and branch-name
• branch, with attributes branch-name, branch-city, and assets