Legacy system is an operational system that has been designed, implemented and installed in a radically different environment. In critical business systems, it can use many legacy systems.
The most appropriate strategic options for evolving these systems are:
1. Scrap the system completely. This option is performed when the system is ineffective to the business process or the business process has changed, leaving the system to be obsolete.
2. Leave the system unchanged and continue regular maintenance. This option is chosen when the system is still required but is fairly stable and change requests is rarely happen.
3. Reengineer system to improve maintainability. This is performed when the system maintenance cost exceeds the cost of reengineering the system.
4. Replace all or part of the system with a new system. This is to be chosen when old system can’t continue operation or where off-the-shelf systems would allow the new system to be developed at a reasonable cost.
It would normally chosen by the replacement option for all or part of a system rather than continue maintenance of the system.
In this situation,
1. The hardware platform for the system is being replaced.
2. The system wishes to standardize on some approach to development that is not consistent with the current system.
3. Some major sub-system is being replaced (e.g. a database system) or where the technical quality of the existing system is low and there are no current tools for re-engineering.
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