Program evolution dynamics is the study of system change. In the 1970s and 1980s, Lehman and Belady (1985) carried out several empirical studies of system change with a view to understanding more about characteristics of software evolution. The work continued in the 1990s as Lehman and others investigated the significance of feedback in evolution processes (Lehman, 1996; Lehman et al., 1998; Lehman et al., 2001). From these studies, they proposed ‘Lehman’s laws’ concerning system change (Figure 9.7).
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