Recovering reusable components from legacy systems by program segmentation

There are many reasons to retire a legacy system. But the system may contain critical business rules and other reusable assets that are not explicitly documented anywhere else. A software reengineering technique called program segmentation is described. It supports the recovery of these reusable assets from old code. This technique consists of a focusing step, which helps the analyst localize, understand, and combine functional pieces in large programs, and a factoring step, which extracts the focused functional pieces and packages them into independent reusable modules