Windowed date fields undergo automatic expansion relative to the century window when they are used as operands in arithmetic expressions or arithmetic statements. However, the result of incrementing or decrementing a windowed date is still treated as a windowed date for further computation, comparison, and storing.
When used in the following situations, windowed date fields are treated as if they were converted to expanded date format:
The details of the conversion to expanded date format depend on whether the windowed date field is numeric or alphanumeric.
Given a century window starting year of 19nn, the year part (yy) of a numeric windowed date field is treated as if it were expanded as follows:
For signed numeric windowed date fields, this means that there can be two representations of some years. For instance, windowed year values 99 and -01 are both treated as 1999, since 1900 + 99 = 2000 + -01.
Alphanumeric windowed date fields are treated in a similar manner, but use a prefix of 19 or 20 instead of adding 1900 or 2000.
For example, when used as an operand of a relation condition, a windowed date field defined by:
01 DATE-FIELD DATE FORMAT YYXXXX PICTURE 9(6)
VALUE IS 450101.
is treated as if it were an expanded date field with a value of: