SDL Modules – Concepts and Tool Support

Abstract

SDL, ITU’s Specification and Description Language, supports developing systems in a modular and hierarchical way, based on structural type definitions and their instantiations. Also, reuse is supported by the possibility to define collections of type definitions, e.g., as SDL packages, that can be used in different systems. Another important development task that can be supported by packages is the replacement of system parts, i.e., structural instances. This can be achieved, for instance, by replacing the type definition to which an instantiation refers by using another package containing a compatible type. However, we have found that this apparently elegant solution reveals some intricacies in practice. To fully exploit the benefits of packages for the development of complex systems and system versioning, type definitions are typically collected in a considerable number of packages. Moreover, there usually are numerous dependencies among packages, which make their management an error-prone task. Finally, it is not clear which types are compatible such that they can be used as mutual replacements. In this paper, we propose a clean solution for the replacement of system parts. Therefore, we introduce a concept that we call SDL module, which we use to capture compatibility of structural type definitions and replacement rules. We illustrate the applicability of our approach by presenting an in-house development tool to automate the replacement process. This tool can be utilized to speed up the development process, and adapt SDL systems to different platforms and scenarios.