Context
Lehman and Belady classified programs into three types:
- S-type programs are those that can be specified formally.
- P-type programs cannot be specified. Instead, an iterative process is used to find a working solution.
- E-type programs are embedded in the real world and become part of it, thereby changing it. This leads to a feedback system where the program and its environment evolve in concert.
The laws of software evolution were originally based on observations regarding the evolution of IBM's OS/360 and OS/370. The laws were not presented as laws of nature, but rather as general observations that are expected to hold for all E-type systems, regardless of specific programming or management practices.
Read more about this topic: Lehman's Laws Of Software Evolution
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