BOM Native Type or Primitive Type Object to Business Object Attribute

car.make = bus.make;
bus.make = "Ford" // will not affect car.make

person1.age = person2.age;
person2.age = person2.age + 1;	// Will not increment person1.age

person1.dob = DateTimeUtil.createDate("1968-01-04");
person2.dob = person1.dob;
person2.dob.setYear(1970); // Value now 1970-01-04; person1.dob
                           // is still 1968-01-04