How to identify a strong vs weak relationship on ERD?

We draw a solid line if and only if we have an ID-dependent relationship; otherwise it would be a dashed line.

Consider a weak but not ID-dependent relationship; We draw a dashed line because it is a weak relationship.

1. Weak (Non-Identifying) Relationship

   • Entity is existence-independent of other enties

   • PK of Child doesn’t contain PK component of Parent Entity

2. Strong (Identifying) Relationship

   • Child entity is existence-dependent on parent

   • PK of Child Entity contains PK component of Parent Entity

   • Usually occurs utilizing a composite key for primary key, which means one of this composite key components must be the primary key of the parent entity.