The Free On-line Dictionary of Computing (30 December 2018):

MSG.84

    A language for the functional specification and
   module design phases of the software life cycle, first
   presented in Berzins and Gray's 1985 paper.  Not unlike PDL.

   ["Analysis and design in MSG.84: formalizing functional
   specifications", Valdis Berzins, Michael Gray, Volume 11 Issue
   8, IEEE Transactions on Software Engineering, Aug 1985].

   (2003-05-15)