title: Primary Key of Associative Entity
body: <p>In this ERD:</p>
  
  <p><a href="https://i.stack.imgur.com/37xRI.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/37xRI.jpg" alt="enter image description here"></a></p>
  
  <p>Certificate Entity is an Associative Entity and it has a unique identifier - Certificate Number. Since an Associative Entity inherits its primary key from other entities. The key field of associated entity are primary key of each end entity is a foreign key on the associated entity, and both foreign keys combined together become a primary key(Concepts from Textbook). </p>
  
  <p>Is the primary key of the Certificate Entity should be a composite key which contains three parts: CertificateNumber, EmployeeID, CourseID ?</p>
  
  <p>Or its primary key is CertificateNumber, and takes EmployeeID, CourseID as attributes of this entity??</p>
  
  <p>I'm confused on this question because normally an associated entity doesn't have its own identifier(Certificate Number). It just take primary keys from other entities combined as composite key(EmployeeID, CourseID), then use that composite key as its identifier.</p>
  
  <p>Thank you</p>
  
  <p>Alex</p>