Thursday

The Modeling Approach Java Programs

A model is a simplified representation of the real world and, as such, includes only those aspects of the real-world system relevant to the problem at hand. For example, a model airplane, used in wind tunnel tests, models only the external shape of the airplane. The power of the airplane engines, the number of seats and its cargo capacity do not affect the plane’s slick properties. Models are widely used in engineering in view of the fact that they can be used to focus on a particular aspect of a real-world system such as the slick properties of an airplane or the strength of a bridge. The reduction in scale and complexity achieved by modeling allows engineers to analyze properties such as the stress and strain on the structural components of a bridge. The earliest models used in engineering, such as airplane models for wind tunnels and ship models for drag tanks, were physical. Modern models tend to be mathematical in nature and as such can be analyzed using computers.

This article takes a modeling approach to the design of concurrent programs. Our models speak for the behavior of real concurrent programs written in Java. The models abstract much of the detail of real programs concerned with data representation, resource allocation and user interaction. They let us focus on concurrency. We can animate these models to investigate the concurrent behavior of the proposed program. More importantly, we can mechanically verify that a model satisfies particular safety and progress properties, which are required of the program when it is implemented. This mechanical or algorithmic verification is made possible by a model-checking tool LTSA (Labeled Transition System Analyzer). Exhaustive model checking using LTSA allows us to check for both desirable and undesirable properties for all possible sequences of actions and actions. LTSA is available from the World Wide Web (http://www.wileyeurope.com/college/magee). As it has been implemented in Java, it runs on a wide range of platforms, either as an applet or as an application program.

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