title: Placement of service methods
body: <p>Let's assume I have two service classes with the following methods:</p>
  
  <ul>
  <li>GroupService
  <ul>
  <li>createGroup()</li>
  <li>deleteGroup()</li>
  <li>updateGroup()</li>
  <li>findGroup()</li>
  </ul></li>
  <li>UserService
  <ul>
  <li>createUser()</li>
  <li>deleteUser()</li>
  <li>updateUser()</li>
  <li>findUser()</li>
  </ul></li>
  </ul>
  
  <p>Now, I am thinking about the aesthetics of theses classes.
  Imagine we want to implement a method which search for all user of a specific group.
  Which service class is responsible for such a method?</p>
  
  <p>I mean, the return value is a user (or maybe a collection of users) but the parameter (which means the name of the group) is a group.
  So which service class is the better place to put this method in?</p>