Weak Entities + Partial Keys + 2NF I'm a bit confused on the concept of weak entities and normalization and couldn't find any answers online. I know that generally weak entities have a partial key to uniquely identify its own records but the primary key is usually a composite key made up of this partial key and the foreign key (that refers to the weak entity's parent's primary key). Before I thought we could just have the foreign key be the sole primary key for the weak entity but apparently this is not such a good idea.  

I am confused however on normalization, specifically 2NF where we have to make sure that no non-prime attribute is solely dependent on a subset of the primary key. 

I'm missing something crucial in my understanding here. So wouldn't a weak entity be in violation of 2nf? Because a non-prime attribute could be dependent solely on the foreign key?
So wouldn't a weak entity be in violation of 2nf? Because a non-prime attribute could be dependent solely on the foreign key?


No.  Consider a typical example:

SalesOrder(OrderId,OrderDate) PK (OrderID)
SalesOrderItem(OrderId,OrderItemNum,ProductId,Quantity,Price) PK (OrderId,OrderItemNum)


No OrderItem non-key attribute is functionally dependent on OrderItemNum.  OrderItemNum could be repeated for multiple orders.  In practice it's often not, but for the purposes of normalization it's just the trailing column of the primary key.