When you create a relationship between two tables, it is usually a good idea to enforce referential integrity. Referential integrity keeps data accurate and ensures that you don’t accidentally change or delete related data in one table but not in the other.
Access creates the relationship between the two tables and enforces referential integrity between them.
The join line between the tables looks different than normal. This relationship indicates that referential integrity is being enforced between the two tables and that the tables have a one-to-many relationship.