A typical ListOf statement provides a list of one object type. You may also create a list that references more than one object type using the HETEROGENEOUSLISTOF keyword.
Example
Definition " Procedure"
{
PROPERTY "Underlying Procedure" { EDIT HETEROGENEOUSLISTOF " Use Case",
Class", "Method", "Use Case Step" READONLY}
..}
In the example above, the “Underlying Procedure” property of the “Procedure” definition can be populated with definitions of the type Use Case, and/or Class, and/or Method, and/or Use Case Step.