title: Do classes in an UML class diagram always translate to entities in a conceptual data model?
body: <p>I'm currently working on a project for my university and one teacher told me I was wrong to think that there could be classes in a UML class diagram (thinking of it as a design diagram) to which there would be no equivalent in a data model. He then pressured me to provide a counter-example to prove my point but I just couldn't think of one.</p>
  
  <p>I checked a few books I had about UML like "Learning UML 2.0," "Applying UML and Patterns" and UML 2 for dummies, but I couldn't find any information regarding which classes appear on a class diagram. I asked him about implementation classes but he told me that they shouldn't be included in a class diagram. So I'm at a loss here.</p>
  
  <p>I also checked this questions before posting:</p>
  
  <p><a href="https://stackoverflow.com/questions/4680231/differences-between-a-conceptual-uml-class-diagram-and-an-erd">Differences between a conceptual UML class diagram and an ERD?</a></p>
  
  <p><a href="https://stackoverflow.com/questions/8578645/generate-uml-from-a-conceptual-data-model">Generate UML from a conceptual data model</a></p>
  
  <p><a href="https://stackoverflow.com/questions/11628287/how-to-relate-data-with-function-in-uml-class-diagram">how to relate data with function in uml class diagram</a></p>
  
  <p>But they don't really solve the question I have.</p>
  
  <p>Thanks for any insight you might have.</p>