Define the relationships

After you select your database entities, you must consider the relationships between them. Relationships are not always obvious, but all the ones worth recording must be found. The only way to ensure that all the relationships are found is to list all possible relationships exhaustively. Consider every pair of entities A and B and ask, “What is the relationship between an A and a B?”

A relationship is an association between two entities. Usually, a verb or preposition that connects two entities implies a relationship. A relationship between entities is described in terms of connectivity, existence dependency, and cardinality.