The latest SDL standard (SDL–96) defines external procedures (i.e., procedures that are implemented outside an SDL system). These procedures can be implemented in languages other than SDL, such as C code.

With the ITU standard Z.105, SDL is combined with ASN.1. This extension to SDL allows a choice between declaring data according to the native SDL syntax or according to ASN.1. ASN.1 modules are treated as SDL packages and can, for example, be shared between an SDL design and a TTCN test suite.

Portability and Scalability

A key feature of SDL is its abstraction mechanisms for seamless portability between cross-compilers and operating systems. Moreover, the same abstraction mechanisms permit the user to choose how to map SDL processes to physical processes, IPC (interprocess communication) schemes, and time according to what is most efficient in each actual case. The same implementation can be used for many different configurations and different kernels, ranging from monotasking small systems to multiprocessor high-end systems.

Distributed Applications

The same abstraction mechanisms that make SDL implementations independent of cross-compilers, operating systems, and IPC and process mapping schemes also make an SDL system independent of distribution architecture and distribution method. This makes SDL the perfect language for modeling and implementing distributed systems. One SDL model supports many physical distribution configurations.