From the README:
OVERVIEWThis directory contains a C++ software toolkit built at NIST for programming with ISO 14649 Parts 10, 11, and 111. Those parts are a data model to be used for control of a machining center. Those Parts are fully covered.
The toolkit supports both (1) direct access to C++ class data and (2) indirect access. Indirect access is provided by making class data private and having public get and set functions for each data item. Direct access is provided by making class data public so that no get or set functions are needed. The names of files using direct access include "Direct".
The toolkit contains four principal items (plus utilities).
C++ class definitions and implementations. A parser for STEP Part 21 files. A simple stand-alone parser/printer. An ISO 14649 interpreter for 3-axis machining. The software is all in standard C++, so it may be compiled and run on any computer for which a standard C++ compiler is available.
The rest of the README
Part of the code was generated by sebnf2pars.