To begin designing a relational database, one must define the by defining each table and the fields in it. primary key physical structure foreign key logical structure

To begin designing a relational database, one must define the Logical structure

Explanation:

Primary key: It is a unique key which uniquely identifies each record in a table. So this does not purely defines the relationship of the table during the beginning of the design.

Foreign key: It is a key which is closely connected to the primary key. The value of the column will accept values only if the values exists in the base table.

Physical structure: This is not going to be related to the relationship of the structure since the storage management is done by Operating system.

Only the logical structure clearly defines the relationship in the database. It will have information about the list of tables and fields. It will also mark the relationship between one table and another.