[database] What's the difference between identifying and non-identifying relationships?

Non-identifying relationship

A non-identifying relationship means that a child is related to parent but it can be identified by its own.

PERSON    ACCOUNT
======    =======
pk(id)    pk(id)
name      fk(person_id)
          balance

The relationship between ACCOUNT and PERSON is non-identifying.

Identifying relationship

An identifying relationship means that the parent is needed to give identity to child. The child solely exists because of parent.

This means that foreign key is a primary key too.

ITEM      LANGUAGE    ITEM_LANG
====      ========    =========
pk(id)    pk(id)      pk(fk(item_id))
name      name        pk(fk(lang_id))
                      name

The relationship between ITEM_LANG and ITEM is identifying. And between ITEM_LANG and LANGUAGE too.

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