Upgrades are the migration from an older version of a product to a newer one. The vendor will usually provide a set of utilities (for example, to move from version X to X+1), but not always. A “not-always” situation would be in the migration from version X to version X+3 or X+4, where intervening versions must be jumped over.
Interfacing with a new system requires the maintenance of the old system along with major testing of the new system. Don’t neglect the importance of ensuring your web interfaces are also up-to-date. As I mentioned, the old system will have valid data for some time.
It may be that the switchover is done on a midnight when the decision taken is to remain on the live system, and not do a fall back. In this case, you will need to address the problem of what to do with your web site interfaces if something goes wrong. For this reason, you should only update these interfaces once you are sure the implementation is a success.
(Yes, some go-lives fail the first time. This happens mainly with large systems because they are of a more complex product design).
Historical Data Migration
Normally, ERP systems have a built-in provision for creating historical data. When is data transferred to historical archives? Some businesses archive data 24 months old, others do it at 36 months.
The move to historical tables is to reduce the number of records in “active tables” so that system response times are reasonable and system backups can be done in the window of time reserved for this operation.
Documentation and training
This is an important critical part of the migration or upgrade process. The usual practice is to make the key users responsible for guaranteeing the training of their respective groups. Any vendor-based courses deemed necessary are held a week or two before going live, sometimes on-site or at other times, off-site.
The last stage prior to “going live” is user acceptance testing (UAT) where the client tries out the system to ensure that everything is working properly and that the developer has fixed all the application bugs.