Identifying relationships losing meaning in relating entity

Question

So as you can see I have an Identifying 1 to many relationship in the tables above.

If I was to change this relationship to a Identifying 1 to 1 relationship, then the auto_leads table will still contain two composite primary keys from its parent leads table. In other words, nothing will change.

Does an identifying relationship have any meaning in the context of relational models? It doesnt appear to change its effect with respect to relationships.

Answer 1

Identifying relationship is an ER-modelling concept which arises because ER modelling assumes there is some semantic significance to having a primary key for each entity. Primary keys have no special role in relational database design and therefore the concept of an identifying relationship is usually of no great importance.

Consider the example of a table with two candidate keys, A and B. A is also a foreign key. According to ER-modelling convention if A is chosen as a primary key then the foreign key relationship is an identifying one. If A is an alternate key then the relationship is deemed to be non-identifying. Yet the form, function, integrity constraints and presumably the business meaning is exactly the same in both cases. The concept of identifying relationships is only as important as you want it to be.