Reactis Validator performs automated searches of models for violations of user-specified requirements. If Validator finds a violation, it returns a test that leads to the problem. This test may then be executed in Reactis Simulator to gain an understanding of the sequence of events that leads to the problem. Validator enables the early detection of design errors and inconsistencies and reduces the effort required for design reviews. Some checks that may be performed with Validator include the following.

• Will a model-variable's value ever fall outside a desired range?
• Will a car's cruise-control maintain vehicle speed within acceptable limits of the set speed?
• Will a plane's thrust reversers ever engage when the aircraft is airborne?
• Will an x-ray machine ever deliver a dangerous dose of radiation?
• Will a cellular phone ``hang'' when moved from a non-serviced into a serviced area?

The figure below shows how engineers use Validator. First, a model is instrumented with assertions to be checked. The tool is then invoked on the instrumented model to search for assertion violations. The output of a Validator run is a test suite that includes tests leading to violations found during the analysis. Validator assertions may be added to any Simulink system or Stateflow diagram in a model.

Validator also offers an alternative usage under which the tool searches for tests that exercise user-defined coverage targets. For example, users can specify a target that requires that a cruise control remain engaged for at least 30 consecutive simulation steps during some test. In the following discussion we shall refer to such coverage targets and assertions as Validator objectives.

Two mechanisms for formulating objectives are supported:

Expression objectives

are C-like boolean expressions.

Diagram objectives

are references to subsystems in Simulink / Stateflow libraries.

Diagram objectives are attached to a model using the Reactis GUI to specify a Simulink system from a library and ``wire'' it into the model. The diagrams are created using Simulink and Stateflow in the same way standard models are built. After adding a diagram objective to a model, the diagram will be included in the model's hierarchy tree, just as library links are in a model.