Trouble deciding on identifying or non-identifying relationship

NickC Said: one-to- relationships are identifying relationships, and many-to-many relationships are non-identifying relationships

The explanation seems totally wrong to me. You can have:

• Ono-to-One Non-identifying Relationships
• One-to-Many Non-identifying Relationships
• One-to-One Identifying Relationships
• One-to-Many Identifying Relationships
• Many-to-Many Identifying Relationships

Imagine you have the following tables: customer, products and feedback. All of them are based on the customer_id which exists on the cutomer table. So, by NickC definition there shouldn't be exists any kind of Many-to-Many Identifying Relationships, however in my example, you can clearly see that: A Feedback can exists only if the relevant Product exists and has been bought by the Customer, so Customer, Products and Feedback should be Identifying.

You can take a look at MySQL Manual, explaining how to add Foreign Keys on MySQL Workbench as well.

Both sound like identifying relationships to me. If you have heard the terms one-to-one or one-to-many, and many-to-many, one-to- relationships are identifying relationships, and many-to-many relationships are non-identifying relationships.

• If the child identifies its parent, it is an identifying relationship. In the link you have given, if you have a phone number, you know who it belongs to (it only belongs to one).

• If the child does not identify its parent, it is a non-identifying relationship. In the link, it mentions states. Think of a state as a row in a table representing mood. "Happy" doesn't identify a particular person, but many people.

Edit: Other real life examples:

• A physical address is a non-identifying relationship, because many people may reside at one address. On the other hand, an email address is (usually considered) an identifying relationship.
• A Social Security Number is an identifying relationship, because it only belongs to one person
• Comments on Youtube videos are identifying relationships, because they only belong to one video.
• An original of a painting only has one owner (identifying), while many people may own reprints of the painting (non-identifying).

I think that an easier way to visualize it is to ask yourself if the child record can exist without the parent. For example, an order line item requires an order header to exist. Thus, an order line item must have the order header identifier as part of its key and hence, this is an example of an identifying relationship.
On the other hand, telephone numbers can exist without ownership of a person, although a person may have several phone numbers. In this case, the person who owns the phone number is a non-key or non-identifying relationship since the phone numbers can exist irrespective of the owner person (hence, the phone number owner person can be null whereas in the order line item example, the order header identifier cannot be null.