Relational Specification of Interface Modules for Real-time Systems

Documentation plays a key role as a component of design process, and a preview of a task before it comes to be executed. A well-specified task might not take less implementation time than one without documents, but one of the obvious advantages is that misunderstandings are avoided and readable specification makes it easy for the successive developers to exploit or modify the software or hardware design. Interface Modules (IM) are modules that encapsulate input or output device hardware and the related software, so that the application software can be written without specific knowledge of the particular devices used. In this work, we present a technique to IM specification that very few researchers pay attention to in the formal specification area. The technique is an extension of the System Requirements Documentation technique presented in [58], which is based on the Software Cost Reduction (SCR) method. Since an IM interacts with both the external environment and other software modules, the technique is used to specify a hybrid of software and corresponding hardware devices. The interface quantities are modeled as functions of time and the behavior is described in terms of conditions, events and mode classes. The contributions of this work to the field of formal specification in general, consists in extending SCR method with introducing access programs and parameterized modes to specify Interface Modules for real-time systems. In the SCR method, conditions are defined as boolean functions of monitored or controlled variables. Such definitions are limited to address the relationship to the environment. For interface modules, we use access programs as conditions so that the relationship of the IMs to other software modules can be expressed. The parameterized modes simplify the specification by grouping a set of modes with particular values in the same mode name. This technique facilitates concise and formal description of the module behav-