systems diagram

In domain analysis or systems design, a systems diagram abstracts a system to make it easier to explain and justify diagnostics and experiments that will determine if the diagram is an accurate model of a domain or a situation.

They attempt to draw "how a system works." There are many versions of systems diagrams.

open loop

An open loop systems diagram shows only the input, process and output. If the system is working correctly the output matches the input. In an open loop diagram how this is done, is not shown, it is assumed to take place by the observer who probably created the diagram in the first place from a God's Eye View that is not part of the diagram itself.

closed loop

Closed loop systems have input, process, output, monitor, feedback, compare and adjust. A comparator checks output to determine if it is expected or desired. Unexpected output and undesired output are treated separately. Undesired output may be a result of undesired input or undesirable process - only a diagnostic can determine which is actually at fault. Usually such diagnostics are not shown, only the routine feedback that regulates the system: a monitor to watch the system, means to adjust/make changes, and feedback - the information flow out of the system about itself. All these elements together close the loop:

The feedback loop includes monitor, comparator, adjust and feedback. In the feedback loop, you look (monitor) at the information (feedback) that you are getting from a system, you compare the output with the input and make adjustments.

causal loop

A causal loop diagram attempts to represent causality more directly. The working parts of such diagrams are often defined into existence by some hypothesis and are not easily observed or experimented on. They are more useful in very abstract decision making situations, especially political or economic ones. They are used more often in very high level domain analysis or systems design, including especially organization design where risk management is critical.


A subsystem is a smaller system operating as part of a much larger system.

This is a cite link - the concepts are related as defined in New York State Standard MST 5.4.