title: INCLUDE statement in the alternate flow of a business use case
body: <p>I'm doing a requirements analysis for a system and currently I try to write the business use cases (BUC) and make business use case diagram. I currently use the following guidelines:</p>
  
  <ul>
  <li><p>When I have optional extra steps for a BUC I use an EXTEND-statement to point to the BUC where these optional steps can be found. Both the BUC that extends and the one that is extended can exist on it's own.</p></li>
  <li><p>When I have duplicate functionality in multiple BUC's I try to extract the this and put it in a separate BUC. Then I use an INCLUDE-statement in the BUC where I extracted the functionality, to point to the BUC where this functionality can be found. The BUC in which you point to the external BUC with the INCLUDE-statement cannot work on it's own.</p></li>
  </ul>
  
  <p>This all worked fine for until I arrived at the following situation:</p>
  
  <ul>
  <li>In the alternate flow of a BUC (let's call this one A) there's duplicate functionality that I already have specified in another BUC (let's call this one B).</li>
  <li>So naturally I want to use the INCLUDE-statement to point to B.</li>
  <li>If I do this I also have to show this in my business use case diagram.</li>
  <li>If I draw an INCLUDE arrow in the diagram (from A to B) it looks like A cannot exist without B.</li>
  <li>However this is not the case, as A only needs B when it's in the alternate flow.</li>
  </ul>
  
  <p>I considered following options:</p>
  
  <ol>
  <li>I keep all the functionality in the the alternate flow, but this makes the alternate flow too long and creates duplicate functionality.</li>
  <li>I use extend instead, but this imposes that B is optional while if you are in the alternate flow of A, you have to go through B.</li>
  </ol>
  
  <p>Any thoughts?</p>