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