title: Three Entity Constraint in Object Role Model in NORMA
body: <p>I am trying to model the constraint depicted in the ORM diagram below using NORMA for Visual Studio 2010:
  <img src="https://i.stack.imgur.com/XmUHh.png" alt="enter image description here"></p>
  
  <p>Merchant transacts in a Currency if and only if that Merchant uses a Processor that supports that Currency.</p>
  
  <p>According to <a href="http://www.objectrolemodeling.com/WebLog/tabid/58/EntryId/40/Join-Path-Subset-Constraints.aspx" rel="nofollow noreferrer">this</a> link, what I am trying to model is a join subset constraint. Here is an example from the link above:</p>
  
  <p><img src="https://i.stack.imgur.com/VLkf5.gif" alt="enter image description here"></p>
  
  <p>Which reads as a Person can only work on a Project if that Person works in a Department that Spansors that Project.</p>
  
  <p>That seems identical to what I am trying to model.</p>
  
  <p>I've tried several combinations if adding a subset constraint, clicking one role then another, but always end up with errors such as:</p>
  
  <ul>
  <li>Constraint 'SubsetConstraint1' in model 'ORMModel1' has role players in column '1' with incompatible types.</li>
  <li>Constraint 'SubsetConstraint1' in model 'ORMModel1' has role players in column '2' with incompatible types.</li>
  </ul>
  
  <p>How can I go about modeling this constraint?</p>