How to identify a strong vs weak relationship on ERD

Question

A dashed line means that the relationship is strong  whereas a solid line means that the relationship is weak  On the following diagram how do we decide that the relationship between the Room and Class entities is strong  Is it because Room entity has a regular key  non-composite

User · Answer

Weak  Non-Identifying  Relationship   Entity is existence-independent of other enties PK of Child doesn   t contain PK component of Parent Entity  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

User · Answer

In entity relationship modeling  solid lines represent strong relationships and dashed lines represent weak relationships

User · Answer

The relationship Room to Class is considered weak  non-identifying  because the primary key components CID and DATE of entity Class doesn t contain the primary key RID of entity Room  in this case primary key of Room entity is a single component  but even if it was a composite key  one component of it also fulfills the condition    However  for instance  in the case of the relationship Class and Class Ins we see that is a strong  identifying  relationship because the primary key components EmpID and CID and DATE of Class Ins contains a component of the primary key Class  in this case it contains both components CID and DATE

User · Answer

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

[entity-relationship] How to identify a strong vs weak relationship on ERD?

Examples related to entity-relationship

Examples related to erd