Work Management Standards › Version Control › Upward Compatibility

Upward Compatibility

A prime objective of version control is ‘upward compatibility’. New versions of applications must always support existing versions or provide a simple conversion route to the new version. Apart from the routine format level considerations, particular considerations apply to different object types:

• Command parameters: Existing command parameter keywords and their default values should not be changed. New keywords may be added (after all existing parameters, or past the limit for positional specification as indicated by the MAXPOS keyword). New values for existing parameters may also be added.
• Program parameters: Existing program parameter interfaces should only be changed if:
  • All references to the called program have also been changed.
  • The change is to add new parameters to the end of the parameter list and the parameter use is optional. For example:
    • Escape messages. The escape messages sent by a program or command in a given set of circumstances should not be changed, nor should the message identifiers of such message be changed (unless all existing programs that call the sending program are also modified).
    • Database files. If new versions of database files are provided, conversion routines for restoring existing data to the new files should be supplied.