4.2.3 Associations and generalisation relationships
Before moving on, it is worth considering briefly the implications of generalisation relationships for associations.
As with attributes, any associations involving a parent class will be inherited by its child class(es). Figure 12 shows two associations involving :
connecting it to
, and
connecting it to
. The meaning of these associations is that any doctor (whether a junior doctor or a consultant doctor) may be linked to a team or to patients or both.
Notice that by including the class the structure is simplified. If
were omitted,
would need to be replaced by two associations, one between
and
, and the other between
and
; there would be similar ‘duplication’ of the
association.
Because inherits an association with
from its parent class,
, there are two different associations between
and
:
and
. This is fine, but it does have some implications for the consistency of the model, in that a team must contain the consultant doctor that heads it. We will return to this later in the course.