How does the transition from a legacy system work?

The three approaches

Specific date. Old on Friday, new on Monday. Sounds simple, but it is the riskiest option: all problems occur simultaneously, under time pressure, and there is hardly any way back.

Parallel operation. Both systems run, one area at a time transitions. More complex, but each step is reversible.

Side by side with an intermediary layer. New functions are developed in the new system, while the old one remains for the rest. Users notice nothing due to an intermediary layer. Complex, but often the only viable way for large systems.

What makes the transition really difficult

Not the technology – the data quality. Years of accumulated data contain duplicates, outdated entries, values in incorrect fields, and special cases that only one person can explain.

No one can take this work off your hands. It should start early, not in the last week.

The proven sequence

1. Inventory: what exists, what is really needed
2. Clean up – in the old system, before the transition
3. Test import into a test environment
4. Sample check by the specialist department
5. Transition of the first area, productive
6. After stabilization: the other areas

What is not in any plan

The period after the transition. Expect several weeks of increased effort: follow-up questions, small corrections, adjustment. Those who do not plan for this will experience the transition as chaos, even though it proceeds normally.