title: Weak Entity Primary Key in Many Identifying Relationship
body: <p>I am designing a distributed database (in ERD) but i am not sure about what will be the primary key of the weak entity "Purchase_Invoice" in SQL as it is related to another weak entity.</p>
  
  <p>P.S: to open the ERD i designed click on <a href="https://drive.google.com/file/d/0B6sa_-V8sfkuNXN0QUY3ZGVGN0E/edit?usp=sharing" rel="nofollow">https://drive.google.com/file/d/0B6sa_-V8sfkuNXN0QUY3ZGVGN0E/edit?usp=sharing</a></p>
  
  <p>Any help would really help. Regards</p>