Rules and boundaries can and should be determined in practical applications rather than in the ontology. For instance, for the purposes of reporting health and public health expenditure, it may be determined that all one-to-one treatment services in clinical settings are not public health services. Another use might determine that some one-to-one clinical treatments, such as those for immunisations, sexually transmitted infections, or drug detoxification, are public health services. The decision to set a constraint or boundary for a particular application should not preclude the wider scope of a 'public health classification', which is developed as an ontology.