Applying the Sliding Window Technique

To apply the sliding window technique correctly, you need to understand the difference between a date format (formerly called a smart date) and a legacy date:

When to Supply Settings for DEFCENT and YRTHRESH

Reference:

Restrictions With MODIFY

The rest of this topic refers simply to DEFCENT when either DEFCENT or FDEFCENT applies, and to YRTHRESH when either YRTHRESH or FYRTHRESH applies.

Supply settings for DEFCENT and YRTHRESH in the following cases:

When you issue a DEFINE or COMPUTE command to convert a legacy date without century digits to a date format with century digits (for example, to convert the format I6YMD to YYMD). With DEFINE and COMPUTE, DEFCENT and YRTHRESH do not work directly on legacy dates; for example, you cannot use them to convert the legacy date format I6YMD to the legacy date format I8YYMD.
When a DEFINE command, COMPUTE command, or Dialogue Manager -SET command calls a function, supplied by Information Builders, that uses legacy dates, the input date does not contain century digits.
On input, the function will use the window defined for an 16 legacy date field (with edit options). The output format may be 18 (again, with edit options), which includes a 4-digit year.

When data is entered or changed in a date format field in a FOCUS data source, or a SQL date is entered or changed in a Relational Database Management System (RDBMS), and the input date does not contain century digits.
For example, you can use the sliging windo technique in applications that use FIXFORM or CRTFORM with MODFIY.

When a data source is read, and the ACTUAL attribute in the Master File is non-date specific (for example, A6, I6, or P6), without century digits, and the FORMAT or USAGE attribute specifies a date format. This case does not apply to FOCUS data sources.

Follow these rules when implementing the sliding window technique:

Specify values for both DEFCENT and YRTHRESH to ensure consistent coding and accurate results, except when YRTHRESH has a negative value. In that case, specify a value for YRTHRESH only; do not code a value for DEFCENT.
Do not use DEFCENT and YRTHRESH with ON TABLE SET.

Finally, keep in mind that the sliding window technique does not change the way existing data is stored. Rather, it accurately interprets data during application processing.

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Reference: Restrictions With MODIFY

The following results occur when you use the sliding window technique with a MODIFY request or FOCCOMP procedure:

A MODIFY request compiled prior to Version 7.0 Release 6, when run with global SET DEFCENT and SET YRTHRESH settings, or with file-level or field-level settings, yields a FOC1886 error message. You must recompile the MODIFY request.
A MODIFY request compiled in Version 7.0 Release 6, when run with global SET DEFCENT and SET YRTHRESH settings, or with file-level or field-level settings, yields a FOC1885 warning message.
A FOCCOMP procedure, compiled with global SET DEFCENT and SET YRTHRESH settings, and run in releases prior to Version 7.0 Release 6, yields a FOC548 invalid version message. You must recompile the MODIFY request.
A FOCCOMP procedure that contains DEFCENT/YRTHRESH or FDEFCENT/FYRTHRESH attributes in the associated Master File, and run in releases prior to Version 7.0 Release 6, yields a FOC306 description error message.