title: How to correctly import modules from a file?
body: <p>My question has 3 parts:</p>
  
  <ol>
  <li><p>Given a file <code>.sig</code> with a signature, how to import it correctly into a file <code>.sml</code> specifying a structure implementation?</p></li>
  <li><p>Given a file <code>.sml</code> specifying a structure implementation, how to correctly import it into other <code>.sml</code> files?</p></li>
  <li><p>Where can I find more information on structuring SML projects? Simple websearch didn't help.</p></li>
  </ol>
  
  <p>I was told that <code>open SomeStructure</code> is not a safe way. I am new to ML-family idioms, hence the question. Thanks.</p>