(VDL) IBM Vienna Labs. A language for formal, algebraic definition via operational semantics. Used to specify the semantics of PL/I. See also href="module.php?name=Lexikon&file=search&eid=1&query=VDM">VDM. ["The Vienna Definition Language", P. Wegner, ACM Comp Surveys 4(1):5-63 (Mar 1972)].