PTOLEMY II - CiteSeerX

Introduction
1.2. In figure 1.2, the block labeled “Sinewave” at the bottom actually represents an instance of a class,
where the definition of the class is given by the block diagram at the top of figure 1.2. In figure 1.4,
that class definition is extended to create a new subclass definition called “NoisySinewave,” whose
definition is shown at the bottom right of the figure. That subclass “inherits” components (actors) and
connections from the base class. The inherited components are outlined with a dashed outline. It then
overrides the definition by adding a second output port, two more override actors and connections
between these. These additions have no dashed outline.
The NoisySinewave class definition is local to the model at the upper left of figure 1.4. That is, the
class definition is part of the model definition and is available for instantiation and subclassing only
within this model. The class definition is shown visually by an icon that is outlined in light blue to distinguish
it visually from an instance. This contrasts with the Sinewave class definition, which is
defined in its own model file, and is accessible to any model that wishes to use it. Thus, Ptolemy II
local class definition
instance
instance
inherited
actors
FIGURE 1.4. Illustration of actor-oriented classes, subclasses, and inheritance.
subclass
execution result
override
actors
top-level class definition
8 Ptolemy II