PTOLEMY II - CiteSeerX

2.7 Classes and Inheritance
Using Vergil
One of the major new capabilities introduced with version 4.0 of Ptolemy II is the ability to define
actor-oriented classes with instances and subclasses with inheritance. The key idea is that you can
specify that a component definition is a class, in which case all instances and subclasses inherit its
structure. This improves modularity in designs. We will illustrate this capability with an example.
2.7.1 Creating and Using Actor-Oriented Classes
Consider the model that we developed in section 2.4, shown for reference in figure 2.34. Suppose
that we wish to create multiple instances of the channel, as shown in figure 2.35. In that figure, the sinewave
signal passes through five distinct channels (note the use of a relation to broadcast the same signal
to each of the five channels). The outputs of the channels are added together and plotted. The result
is a significantly cleaner sine wave than the one that results from one channel alone 1 . However, this is
FIGURE 2.31. Custom icon for the Channel actor.
1. In communication systems, this technique is known as diversity, where multiple channels with independent
noise are used to achieve more reliable communication.
66 Ptolemy II