Previously, we discussed the core database elements: entities, records, and fields. Another important element of databases is the relationship between entities/records.

The database defines the relationships between record types. Relationships between entities dictate the relationship between records.

Entities are related to one another in set ways, often in a hierarchical manner. For example, contact records belong to accounts. Accounts can have one contact record that is the primary contact.

ACCOUNTS
PRIMARY CONTACT
CONTACTS

These relationships also often have restrictions, such as the number of entities allowed. Thus, an account record may have only one primary contact record, but can have many related contact records.