Supporting Behavioral Contracts for COM Components

Specifying behavioral specifications for components apart from the conventional syntactic interface specifications can be very useful in component based system development. Preconditions and postconditions describe one form of behavioral aspects of components. We discuss a tool and an implementation mechanism to incorporate behavioral contracts expressed in terms of preconditions and postconditions for COM components. A method invocation on a component is executed only if the precondition is satisfied. Similarly, the results are successfully returned upon successful execution of the postcondition. A design criterion was to facilitate contract specifications for existing components with least amount of changes at client and server side code. The tool requires that the component should implement an additional interface called IAccess if the behavioral contract needs component state. No modification is required to existing clients of the component.