Definition; Why?

What to fix

• Hardware / ROM
• Operating System
• Compiler: e.g. Old COBOL compilers which gives just YY, RM/COBOL-85
• Application Software

How to fix Application Software

1. Field Expansion: expand YY to YYYY
   Advantages
   
   • straightforward code changes
   • minimum testing, cheaper maintenance
   Disadvantages
   
   • Change of database (files) and other application programs
   • more storage required
   • the year 10,000 problem!
2. Century Window: interpret YY as YYYY
   • Fixed Window: hard coded interpretation. For example, 60 thru 99 implies 1960 thru 1999 and 00 thru 59 implies 2000 thru 2059.
   • Sliding Window: Generalized version of the fixed window method. Subtract X from the current year (CCYY) to get the first year in the 100-year cycle. For example, assume X is 50 and the current year is 1998. In this case, 48 thru 99 implies 1948 thru 1999. 00 thru 47 implies 2000 thru 2047. The meanining of X is the number of past years to maintain.
     When X = 99, future dates are NOT to be used.
     When X = 0, past dates are NOT to be used.
   Advantages
   
   • No database (file) changes
   Disadvantages
   
   • inherently, the year range is limited (00 thru 99)
   • complex to modify programs, error-prone
   • increased maintenance cost
3. Transformation
   • YYYY to BB (binary) which can be decoded as YYYY
   • YYMMDD to YYYDDD
   • YYMMDD to BBBB (binary) which can be decoded as YYYYMMDD
   Advantages
   
   • No database (file) expansion
   Disadvantages
   
   • complex to modify programs, error-prone
   • increased maintenance cost
   • must translate whenever externalized. Can't read files
4. Re-engineering