title: UML sequence for validation before saving
body: <p>I'm new to UML but I'm tasked to draw some UML diagrams that describe some complex parts of our system.</p>
  
  <p>One of these parts is the saving of data in the db, and the steps said data goes through before it can actually be saved.</p>
  
  <p>These are roughly the steps involved:</p>
  
  <ol>
  <li>User wants to save</li>
  <li>App validates that all mandatory fields have values set</li>
  <li>If not valid, app shows a message. If valid, app sends a post request</li>
  <li>The controller maps the dto to the domain model object and passes it to the service layer</li>
  <li>Service layer validates the model according to business rules. If not valid, throws a validation exception</li>
  <li>If valid, model moves down to the data access layer, where EF is used to commit the changes to the db</li>
  <li>On trying to commit, EF might throw a validation exception (mapping) or database exception (bubbled up from the db itself)</li>
  <li>If commit succeeds, the model is passed to the controller which maps it back to its dto counterpart and displayed to the user</li>
  <li>If validation or database exception is thrown, these are displayed to the user</li>
  </ol>
  
  <p>So far this is what I came up with:</p>
  
  <p><a href="https://i.stack.imgur.com/BY94v.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BY94v.png" alt="Sequence Diagram"></a></p>
  
  <p>Is this good enough to display the above steps or might there be improvements to the diagram?</p>