Identifying relationship - where the child entity's identity/existence relies solely on the parent entity. No parent entity means no child entity. For example, if you delete an order (order table), you probable want all the order's line items to disappear as well (order_line_item), because line items without an order are pointless. So an order line item's identity is solely dependent on a matching order existing.
Non-identifying relationship - the child entity can stand on its own without the parent entity. For example, if you have an author table and a book table. Maybe you want to store data about a book, but you don't know who the author is. The book's identity/existence is independent of having the author information.
For an identifying relationship, you put the primary key column from the parent into the primary key column of the child (along with other columns needed to provide uniqueness).
For a non-identifying relationship, you put the primary key column of the parent into the table of the child, but not in the primary key.
Andrew Simkovsky
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