This statistical clustering algorithm arrives at subsystems by minimizing the interaction of problem requirements that each one deals with. This method relies upon a consideration of all such constraints, again leading him to argue for empirically and experientially guided analysis. Even though exemplified with architectural artifacts, Alexander's concerns and methods apply equally well to software systems, subsystems, objects, etc. While there are many obvious differences between houses and software, most are matters of degree at this level of discussion. More of a software design is hidden from its users.
Software generally has many fewer physical constraints.
None of these have much bearing on methodological issues. These themes form a basis for most of Alexander's later writings. These problems, along with observations that people blindly following such methods do not always create better products, led to work increasingly removed from mainstream architectural design practices. Patterns Timeless and Patterns were written as a pair, with the former presenting rationale and method, and the latter concrete details. In Timeless , Alexander describes common, sometimes even universal patterns of space, of events, of human existence, ranging across all levels of granularity.