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Chapter 3
Director). Alternatively, workflow components can execute in parallel, with one or more
components running simultaneously (which might be the case with a PN Director).
A small set of commonly used directors come packaged with Kepler (Table 3.1), but
more are available in the underlying Ptolemy II software that can be accessed as needed.
For a more detailed discussion of workflow models of computation, please see Section
5.2 Choosing a Director, or refer to the Ptolemy II documentation.
The SDF Director is often used to oversee fairly simple,
sequential workflows. Types of workflows that run well
under an SDF Director include processing and
reformatting data, converting one data type to another,
and reading and plotting a series of data points.
The PN Director is often used for managing workflows
that require parallel processing on distributed computing
systems.
The CT Director is designed to oversee workflows that
predict how systems evolve as a continuous function of
time (i.e., "dynamic systems").
The Continuous Director is for the “continuous time”
domain, a timed domain that supports continuous-time
signals, discrete-event signals, and mixtures of the two.
There is a global notion of time that all the actors are
aware of.
The DE Director is often used for modeling timeoriented systems: queuing systems, communication
networks, and occurrence rates or wait times.
The DDF Director is often used for workflows that use
looping or branching or other control structures, but that
do not require parallel processing (in which case a PN
Director should be used).
Table 3.1: Directors that come in the standard Kepler component library.