title: Which layer of the application should contain DTO implementation
body: <p>Lately I've been hearing a lot about DTOs and how useful they are but I can't find a good example of using it in ASP.NET context.</p>
  
  <p>Let's say I use three tier architecture:</p>
  
  <ol>
  <li>Data layer(using Entity Framework)</li>
  <li>Business Layer(WCF Service)</li>
  <li>Presentation Layer (MVC 4.0 web application)</li>
  </ol>
  
  <p>Where should I convert from the EF Employee object to an EmployeeDTO POCO?</p>
  
  <p>Lets say I do the conversion in the Data Access layer but what happens in the WCF service? Should it then be converted to another <code>DataMember</code> object and when it get's to the UI layer(MVC web app) should it then be converted for the third time to a model? I would appreciate it if someone could please clear this for me</p>