title: Does Entity Framework support a parent referring to 0..1 children with a child referring to 1 parent?
body: <p>I have two tables. One is <code>Request</code> and the other is <code>Response</code>. Each request has a <strong>nullable</strong> foreign key reference to a<code>Response</code> record.</p>
  
  <p>Each <code>Response</code> record has a <strong>non-nullable</strong> foreign key reference to the <code>Request</code> entry that it came from.</p>
  
  <p>I'm trying to generate the entities for this model and it fails validation with the error: <code>Multiplicity is not valid in role Response [...]. Because the dependent role properties are not the key properties, the upper bound of the multiplicity of the dependent role must be *</code>.</p>
  
  <p>The mapping that fails:</p>
  
  <p>Request -[0..1]-> Response</p>
  
  <p>Response -[1]-> Request</p>
  
  <p>Why doesn't this work? I know EF doesn't like foreign keys much, but this seems simple enough.</p>