createStudentAccount(ident username, ident studentId, string lastName, string firstName, string email, string password, string code) {
  assume not exists //accounts/account[username];
  assume count(studentId, //accounts/account/student/id) = 0;
 
  insert //accounts
    <account username=[username] lastName=[lastName] firstName=[firstName] email=[email] password=[password] code=[code]>
      <student id=[studentId] />
    </account>
}