title: What is a Primary/Foreign Key Field in this Database Model?
body: <p>I'm looking at this database model and I'm confused about the "PF" in some of the tables. My understanding is that the PF is a "Primary/Foreign key" which could also be a composite key. I understand this situation for a many-to-many relationship, but what about situations such as the <code>Menu_Courses</code> table? The primary key would obviously be an auto-incremented column of type int, but what about the <code>menu_id</code> field? How would that be implemented in a database such as SQL Server? </p>
  
  <p>The author also explains PF fields on this page: <a href="http://www.databaseanswers.org/tutorial4_db_schema/tutorial_slide_5.htm" rel="noreferrer">http://www.databaseanswers.org/tutorial4_db_schema/tutorial_slide_5.htm</a></p>
  
  <p><img src="https://i.stack.imgur.com/dRK2i.gif" alt="http://www.databaseanswers.org/data_models/recipes/index.htm"></p>