Patent attributes
A list of object classes is displayed to the user, and next to each listed object class, a first button is displayed for the user to click on to add, to the user's inventory, instances of the listed object class that the user has. Also, next to the each listed object class, a second button is displayed for the user to click on to identify instances of the listed object class that the user would like to buy. The first button is labeled with a number indicating how many instances of the listed object class that the user has. In a preferred implementation, the second button is labeled with a number indicating how many instances of the listed object class that the user would like to buy, and a third button is labeled with a number indicating how may instances of the listed object class that the user would like to sell.