Above the Line, Below the Line

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Above the Line, Below the Line
Communications of the ACM, March 2020, Vol. 63 No. 3, Pages 43-46
By Richard I. Cook

People who work above the line routinely describe what is below the line using concrete, realistic language. Yet, remarkably, nothing below the line can be seen or acted upon directly. The displays, keyboards, and mice that constitute the line of representation are the only tangible evidence that anything at all lies below the line.


People working above the line of representation continuously build and refresh their models of what lies below the line. That activity is critical to the resilience of Internet-facing systems and the principal source of adaptive capacity.


Imagine all the people involved in keeping your Web-based enterprise up and running suddenly stopped working. How long would that system continue to function as intended? Almost everyone recognizes the “care and feeding” of enterprise software systems requires more or less constant attention. Problems that require intervention crop up regularly—several times a week for many enterprises; for others, several times a day.


Publicly, companies usually describe these events as sporadic and minor—systemically equivalent to a cold or flu that is easily treated at home or with a doctor’s office visit. Even a cursory look inside, however, shows a situation more like an intensive care unit: continuous monitoring, elaborate struggles to manage related resources, and many interventions by teams of around-the-clock experts working in shifts. Far from being hale and hearty, these are brittle and often quite fragile assemblies that totter along only because they are surrounded by people who understand how they work, how they fail, what can happen, and what to do about it.

What’s Going On?

The intimate, ongoing relationship between tech software/hardware components and the people who make, modify, and repair them is at once remarkable and frustrating. The exceptional reach and capacity of Internet-based enterprises results from indissolubly linking humans and machines into a continuously changing, nondeterministic, fully distributed system.


The Line of Representation

All these features are simultaneously products of the environment and enablers of it. They have emerged in large part because the technical artifacts are evolving quickly, but moreso because the artifacts cannot be observed or manipulated directly. Computing is detectable only via representations synthesized to show its passing. Similarly, it can be manipulated only via representations.

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About the Author:

Richard I. Cook, M.D., is an expert in safety, accidents, and resilience in complex systems. His 30 years of experience includes work in medicine, transportation, manufacturing, and information technology. He is the author of the oft-cited “How Complex Systems Fail” and “Going Solid: A Model of System Dynamics and Consequences for Patient Safety.”

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