Laws of Program Evolution Program Evolution: Processes of Software Change (Lehman & Belady)
				• P-type programs – Well-defined, precisely specified – The challenge is efficient implementation – Ex: sort • E-type programs – Ill-defined, fit into an ever- changing environment – The challenge is managing change • Also, S-type programs – Ex: chess
		• Law of continuing change • “A large program that is used undergoes continuing change or becomes progressively less useful.” – Analogies to biological evolution have been made; the rate of change in software is generally far faster