The staged model of software lifecycle consists of initial development, evolution, servicing, phaseout and closedown.
Initial development produces the first running version.
Evolution carries out substantial changes in requirements, structure, and other software attributes. However software can lose its evolvability through the loss of structure or through the loss of necessary knowledge or both. If that happens, software enters the stage of servicing where only minor changes can be made. Finally it enters the stage of phaseout where changes are no longer made, and closedown where it is discontinued. The talk will concentrate on several issues raised by this model, particularly the properties of software change, which is a backbone of both evolution and servicing.