title: Same interface in different domains/project
body: <p>I got this issue:</p>
  
  <p>Product class in a SQLBackend that implements IProduct interface.</p>
  
  <p>I also got a Product in SAPBackend (ERP,  accounting software) that implements the same IProduct.</p>
  
  <p>Both backend is in a different project.</p>
  
  <p>I want to be able to use pass a Product between this two project so I need the same common interface.</p>
  
  <p>I was thinking placing IProduct in a common interface project but if had many common cases would that lead quite many interfaces in that project. And if just lead to that I expose those interfaces to quite many projects</p>
  
  <p>I wonder if there is a better case so SAPBackend and SQLBackend stand by them self and still share a common interface?</p>
  
  <pre><code>namespace Interfaces
  {
      public interface IProduct
      {
          string name {set; get;}
      }
  
  }
  namespace Sqlbackend
  {
      public class Product : IProduct
      {
          public string name { set; get; }
       }
  }
  namespace ERPbackend
  {
      public class Product : IProduct
      {
          public string name { set; get; }
      }
  }
  </code></pre>