title: Are class members mandatory?
body: <p>I remember reading (or hearing) somewhere a few years back that classes must have either an operation, an attribute and an operation, or at least an attribute as a mandatory requirement -- not empty. What I'm asking is whether it's a violation of the Software Engineering rules to have an empty class, or a class with either attributes or operations without the other.</p>
  
  <p>I just want to make sure so that my class diagrams are correct for my project.</p>
  
  <p>Thank you.</p>