title: Database Access Layer
body: <p>I am using Visual Studio 2012 and i have created a .sdf and .edmx for my database. 
  I was wondering what would be the best way to set the relationships between the entities. 
  I have tried just setting the association with the multiplicity set and get an error saying that they are not mapped. 
  Also how do you set the foreign keys. 
  I am trying to create a estate agent like system to book appointments online and in branch. I am creating it in C#. </p>