The finger in the figure above is one such object. Authors can double-click on an object like this to open an object data view of the object, such as the one shown in the figure below. An object data view of an object shows its name, together with a list of its attributes with their values and their rules, if they have any. In this figure, there is a rule for the attribute name pulse. The present value of this attribute is determined by the rule, which refers to the attribute of another object.
Some attributes directly control the appearance of graphical objects.
When the values of such attributes are changed, objects may disappear or move or stretch or rotate or change color, and so on. In constraint-based behavior authoring, authors write rules that specify the values of attributes. Whenever any values in the simulation change, the rules all affected rules are automatically re-evaluated in the proper order to produce new values. The constraint-based approach unburdens authors from concerns about the flow of control in their simulations, and allows behavior specification to be localized. Authors can also write event-based behaviors to achieve special effects or to specify simultaneous behaviors.