Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

Comparisons involving the DATE attribute and a literal

If you are making comparisons in which one comparand has the DATE attribute and the other is a literal, the compiler issues a W-level message. Further compiler action depends on the value of the literal as follows:

  dcl start_date char(6) date;
  if start_date >= '' then /* no windowing */
  ...
  if start_date >= '851003' then /* windowed */
  ...
Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide