public Set<Resource.Type> getAdditionalForeignKeys() {
    return m_setForeignKeys == null ? Collections.emptySet() : m_setForeignKeys;
  }
Get the set of additional foreign key properties that are included in the resource by default.

@return  set of additional foreign key properties
ambari-server/src/main/java/org/apache/ambari/server/api/resources/SubResourceDefinition.java