Structure Definition Language (SDL) Grammar.
SDL is a language used to provide a common definition of data structures that could be exported and shared by various programming languages. Many applications as well as the VMS Operating System and associated tools and utilities were written in a variety of programming languages. SDL itself contains modules written in Bliss, PLI, and Macro Assembler. It also uses tool written in Pascal.
SDL was written at Digital Equipment. HP inherited the product after it took over Compaq, which had taken over Digital Equipment. SDL is still in use today at VMS, Inc which now owns the VMS operating system on all platforms except the VAX. It has ported the VMS operating system to the x86 platform.
The following description of SDL is taken from: Guide to the HP Structure Definition Language *
The HP Structure Definition Language (HP SDL) is used to write source statements that describe data structures and that can be translated to source statements in other languages. You can include the resulting output files in a corresponding target language program for subsequent compilation.
Because HP SDL is compiler- and language-independent, it is particularly useful for maintaining multilanguage implementations. For example, you can create and later modify a single HP SDL source file that can be translated to multilanguage output files; any number of these output files can then be included in one or several multilanguage programming applications.
HP SDL supports the following OpenVMS languages: • HP Ada • HP BASIC • HP BLISS • HP C/C++ • HP DATATRIEVE • HP OpenVMSDCL • HP FORTRAN • HP MACRO • HP Pascal • Kednos PL/I • SDML • DECTPU • UIL
During efforts to port SDL to new platforms it was rewritten in C++ due to the lack of a PLI compiler. The original version was released by HP as freeware. The software as well as the source code is available from VMS, Inc at:
https://vmssoftware.com/community/freeware/