Objectives
The number of large systems being built from scratch is diminishing, while the number of legacy systems in use is very high. While the functionality of existing systems remains constant, the context of new systems, such as the application environment, system level hardware and software, are different. Enhancements to the functionality of the existing systems may also be needed, but although the Migration & re-engineering effort may configured for enhancements, they should not be incorporated until after the Migration & re-engineering is complete. This allows for comparison of functionality between the existing system and the new system. The problem is that systems currently in use, "legacy" systems, have become lacking in good design structure and code organization, making changes to the software difficult and costly. Corporations do not want to "trash" these systems because there are many built in subtle business application processes that have evolved over time that would be lost. Often the developers of the legacy systems are not available to verify or explain this information; the only source is the current software code. The original expense of developing the logic and components of the software systems should not be wasted, so reuse through Migration & re-engineering is desired.

The challenge in application Migration & re-engineering is to take existing systems and instill good software development methods and properties, generating a new target system that maintains the required functionality while applying new technologies. Although specific objectives of a Migration & re-engineering task are determined by the goals of the corporations, there are four general Migration & re-engineering objectives:

1. Preparation for functional enhancement
2. Improve maintainability
3. Migration
4. Improve reliability