The user creates new objects by picking them from an infinite stack of objects, i.e. the pile that is like a factory producing objects. To create a new object, the user either drags it from the pile, or he selects the pile and clicks somewhere, where the object can be created.
The pile where the objects come from does not need to be static; the user may edit the properties of the pile to create different kind of objects.
In most cases, the created objects become independent of the pile, meaning that changes made on the pile properties affect only the objects that are created in the future, not objects that created in the past. However, if the changes in the pile also affect objects created in the past, this connection is an example of the Master and Instances problem.
Example 1: Tabulators in Microsoft Word
The user creates new tab stops in Microsoft Word by clicking the tab area, which creates a new tab object from the pile on the left. The tab pile is now in the state of creating left alignment tab stops, which can be seen from the icon of the pile.
Example 2: Train editor [Nevalainen99]
The user creates a new cargo car by dragging the car object from the pile to the train. The palette on the left consists of four ‘infinite’ stacks of different car types.
Nevalainen S., Ranta J.,
Design project of the User Interfaces course.
Department of Computer Science, University of Helsinki, 1999.