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Legacy System Modernization Strategies

July 2001 Technical Report
Robert C. Seacord, Santiago Comella-Dorda, Grace Lewis, Patrick R. Place, Daniel Plakosh

This 2001 report discusses alternative development approaches for incrementally modernizing legacy systems.


Software Engineering Institute

CMU/SEI Report Number



Modernization of legacy enterprise systems introduces many challenges due to the size, complexity, and frailty of the legacy systems. Size and complexity issues often dictate that these systems are incrementally modernized, and new functionality is incrementally deployed before the modernization effort is concluded. This in turn requires that legacy components operate side by side with modernized components in an operation system—introducing additional problems. 

In this report we discuss some alternative development approaches for incrementally modernizing legacy systems, including consideration of the advantages and disadvantages of each approach. These development alternatives can be mapped against the peculiarities of a particular modernization effort to recommend an appropriate approach.