# pretty much the canonical addStudent procedure
addStudentId(ident username, string id) {
  assume exists //accounts/account[username]; # implicitly true in OO implementations
  assume not exists //accounts/account[username]/student;
  assume count(id, //accounts/account/student/id) = 0;
 
  insert //accounts/account[username] <student id=[id] />;
} # roles: admin