Let's assume I have two service classes with the following methods:

• GroupService
  • createGroup()
  • deleteGroup()
  • updateGroup()
  • findGroup()
• UserService
  • createUser()
  • deleteUser()
  • updateUser()
  • findUser()

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?

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?