title: draw UML class diagram with Service classes
body: <p>this is a small scenario of a big system.
  i want to model this scenario in class diagram and then implement it in code</p>
  
  <p>this is a scenario in book store.there is customer and books
  customer can buy books,search books by name,and read books</p>
  
  <p>class diagram implemented in following ways</p>
  
  <p>1.put all operations to the customer class because customer is the one who perform these actions
  but <code>buyBooks(),searchBook(),readBooks()</code> methods are not responsible for changing the state of customer class
  (these methods are not working on data inside of customer class ) there for it violate basic oop principle encapsulation.</p>
  
  <p>customer can buy,search,read 1 or more books therefore association marked as shown in image.</p>
  
  <p>i have found lots of class diagrams draw this way when referring the INTERNET </p>
  
  <p><a href="https://i.stack.imgur.com/gzA82.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/gzA82.jpg" alt="enter image description here"></a></p>
  
  <p>2.
  put all operations to the customer class same as above.
  and mark each associations seperately, with three separate lines</p>
  
  <p>associations</p>
  
  <ul>
  <li>customer can buy one or more books</li>
  <li>customer can search one or more books</li>
  <li>customer can read one or more books</li>
  </ul>
  
  <p><a href="https://i.stack.imgur.com/rtgUQ.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rtgUQ.jpg" alt="enter image description here"></a></p>
  
  <p>3.in here put all operations to the service class because those methods are not responsible for changing state of neither customer,book class</p>
  
  <p>and then mark association.</p>
  
  <p><a href="https://i.stack.imgur.com/hN1SY.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hN1SY.jpg" alt="enter image description here"></a>
   - among theses which one is correct class diagram ?<br>
   - is it  acceptable to draw service classes in uml class diagrams ?</p>