[bestham]

The definition of a complex system is the qualifier for the quote. Many systems that are designed, implemented and found working are not complex systems. They may be complicated systems. To paraphrase Dr. Richard I. Cook’s ”How Complex Systems Fail” where he claims that complex systems are inherently hazardous, operate near the edge of failure and cannot be understood by analyzing individual components. These systems are not just complicated (like a machine with fixed parts) but dynamic, constantly evolving, and prone to multiple, coincidental failures.

A system of services that interact, where many of them are depending on each other in informal ways may be a complex system. Especially if humans are also involved.

Such a system is not something you design. You just happen to find yourself in it. Like the road to hell, the road to a complex system is paved with good intentions.

[codeflo]

Then what precisely is the definition of complex? If "complex" just means "not designed", then the original quote that complex systems can't be designed is true but circular.

If the definition of "complex" is instead something more like "a system of services that interact", "prone to multiple, coincidental failures", then I don't think it's impossible to design them. It's just very hard. Manufacturing lines would be examples, they are certainly designed.

[estearum]

The manufacturing lines would be designed, and they'd be designed in an attempt to affect the "design" of the ultimate resulting supply chain they're a part of. But the relationship between the design of some lines and the behavior of the larger supply chain is non-linear, hard to predict, and ultimately undesigned, and therefore complex.

The design of the manufacturing lines and the resulting supply chain are not independent of each other -- you can trace features from one to the other -- but you cannot take apart the supply chain and analyze the designs of its constituent manufacturing lines and actually predict the behavior of the larger system.

AFAIK there's not a great definition of a complex system, just a set of traits that tend to indicate you're looking at one. Non-linearity, feedbacks, lack of predictability, resistance to analysis (the "you can't take it apart to reason about the whole" characteristic mentioned above"). All of these traits are also kind of the same things... they tend to come bundled with one another.

[marcosdumay]

A complex system is one that has chaotic behavior.

(And no, this is not "my" definition, it's how it's defined in the systems-related disciplines.)