CEISAR - Center of Excellence in Enterprise Architecture > Transform the Enterprise > How to simplifiy legacy systems ? > Chapter 3 : Proposing a process to implement transformation and replacement
Chapter 3 : Proposing a process to implement transformation and replacement
To actually deliver simplification, CEISAR describes in more details two simplification strategies: the Transformation Strategy and the Replacement Strategy.
- First, Isolate the Blocks that are within the scope from those which are outside. This should be done with minimum impact on the Blocks outside of the scope, to avoid scope propagation.
- For Transformation:
- Build Data Access Services and reengineer Blocks to use them; migrate data
- Isolate reusable Business Functions and expose them as Software Services
- Re-interface Blocks and remove dead parts
- For Replacement:
Choose between two execution approaches:
- In the Big-Bang approach, migration is easier and faster but transition is more brutal and must be thoroughly prepared. It requires precise understanding of the Functions of the legacy and proper testing with a pilot phase on a Product or Organization subset of the Enterprise.
- In the Parallel Execution, the new System runs in parallel and in sync with the old System during a transition phase. It requires great care in the Architecture and costs more but reduces risk, improves progressiveness and often allows earlier business benefits.