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OS/390. Therefore, it is not required to freeze or follow up development,
enhancement, or maintenance of applications during the conversion.
32.2.2.3 Mass Conversion (Switchover)
The actual mass conversion, called the switchover, often takes place over a
single weekend. Before switchover, the production workload runs under VSE.
After switchover, the production workload runs under MVS.
The switchover is the key advantage of using Cortex-MS as a conversion tool. It
eliminates the migration problems related to running some applications under
VSE and some under MVS for an extended period of time. It eliminates the need
to maintain both MVS and VSE versions of files. It allows maintenance and
development work to be done on the VSE versions of programs right up until the
actual mass conversion, and the program converted is the latest working VSE
version.
32.2.2.4 Automation Limits
Some non-standard source code modifications must be performed manually,
either because they are too complicated to automate, or because they are in
very low occurrences. In both cases, automating the process would not be cost
effective when compared to a manual modification. Manual modifications
complement the automated conversion (before or after). They can be applied as
VSE positioning, or manual OS/390 conversion.
Modifications applied to the VSE version of the source code, which is then tested
and installed in production under VSE is known as ″VSE Positioning″. This
technique is consistent with the repetitive conversion approach because it does
not require freezing any source code. For example, VSE COBOL programs must
be manually positioned to:
•
Move STOP RUN statements outside INPUT (or OUTPUT) SORT PROCEDURE,
•
Remove any access to I/O buffers before the file is opened or after the file is
closed,
•
Remove some undocumented features of COBOL Report Writer,
•
Remove the use of the DISPLAY verb to imbed lines into a report written
with the WRITE verb.
Modifications applied to the OS/390 version after automated conversion are
known as ″OS/390 Freeze″. Here a procedure is defined to automatically identify
and manually duplicate the VSE maintenance to the OS/390 ″frozen″ source code
throughout the project. Manual OS/390 conversion is limited to exceptions
because it is incompatible with the repetitive conversion approach.
After switchover, all production is done with the MVS versions of your
applications. The programs that Cortex-MS translates become genuine MVS
programs and are not emulated.
32.2.3 Mass Conversion Tools
Software tools suitable for mass conversion must automate most of the
conversion of VSE JCL, programs and files to native OS/390 without any custom
modification.
In addition, to accommodate the large diversity of coding patterns between VSE
sites, the mass conversion tools must be flexible. Run-time options and exit
Chapter 32. Conversion Process 489