A resource (Resource) can be scheduled to be used at any time, this is represented internally with Appointments There is one Appointment per resource-task pair
The class DoubleListViewBase provides a double listview where the right listview (the slave) containes columns of double values and the left listview (the master) is the 'item' listview and also provides for a sum total column of the values in the slave listview
Any Node will store how much time it takes to complete the node (typically a Task) in the traditional scheduling software the effort which is needed to complete the node is not simply a timespan but is stored as an optimistic, a pessimistic and an expected timespan