The description file contains rules that describe how the  components
    of  your system are related and how MMS is to build them.  You create
    and modify  a  description  file  with  any  text editor (or by using
    MMS/GENERATE);  once the description file exists, you need issue only
    a simple MMS command to update your system.

    A description file contains dependency rules  and  can  also  contain
    macro definitions, directives, and user-defined rules.