ment implementation by
OPCAT1 [ 5] embodies the
assumptions. Stateful objects
(things existing in some state) and
processes (things that transform
objects by creating or destroying
them or by changing their states)
are the building blocks of OPM.
Structural and procedural links
express static and dynamic relations among entities—objects,
object states, and processes—in
the system, and a number of
refinement/abstraction mechanisms are built into OPM for
complexity management.
(a)
DUAL-CHANNEL PROCESSING
Following the dual-channel
assumption, the brain simultaneously engages the visual and verbal channels (likely the two brain
hemispheres) for conveying ideas
regarding the system’s architecture. Indeed, OPM represents
knowledge about the system’s
structure and behavior—
pictorially and verbally—in a single
unifying model. When the user
expresses a piece of knowledge in (b)
one modality—graphics or
text—the complementary one is Figure 1. Top-level
automatically updated so the two OPD built in stages. (a) OPCAT user
remain coherent at all times. interface, showing the
To illustrate how to account for initial system diagram of
the cognitive assumptions, I fol- the anti-lock braking system (top) and
low a stepwise example of the its OPL textual
modeling of a car’s anti-lock brake specification (bottom)
in which the object
system (ABS). Figure 1(a) outlines Car-Driver System is
OPCAT’s graphical user interface, affected by the process
simultaneously displaying the Emergency Braking; (b) the states speeding
graphic (top) and text (bottom) and stopped are added
modalities needed to exploit to the Car-Driver
System; (c) the
human dual-channel processing. input/output link pair is
The top-right pane presents the added from the input
model graphically in an Object- state to the process and from the process to the
Process Diagram (OPD); the one output state.
below it in Figure 1(a) lists the
same model textually in Object-Process Language
(OPL). OPCAT recognizes OPD constructs (symbol
patterns) and generates their OPL textual counter-
(c)
1A research version of OPCAT is available for freedownload at
www.opcat.com/downloads/restricted.
parts. OPL is a subset of natural English, and each
OPD gives rise to a textual OPL equivalent sentence
or phrase.
For example, Emergency Braking, the central
system’s process, is the blue ellipse in Figure 1(a), and
Car-Driver System is an object (green box)
affected by and benefiting from Emergency Braking. This object-process connection is expressed by
linking Car-Driver System to Emergency Braking via an effect link—a bidirectional arrow indicating that the process affects the object by changing its
state from unspecified input state to unspecified output state. As soon as the modeler joins the object with
the process through the link, the first OPL sentence,
“Emergency Braking affects Car-Driver System,” shows up in the OPL pane of Figure 1(a).
As the example shows, the OPL syntax is designed
to generate sentences in plain, natural (albeit
restricted) English. Unlike programming languages,
OPL names can be phrases (such as Emergency
Braking). As a subset of English, OPL is accessible to
nontechnical stakeholders, and other languages can
serve as the target OPL. To enhance the text-graphics