<aside> 🚩 A system diagram is a visual model of a System, its components, and the System Interfaces between those components. With supporting documentation, it can capture all the essential information of a system's design. There are many variations of diagramming style that all fall under this design artifact. The style presented here is intended to be consistent with the rest of this courseware.

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What is a System Diagram?

Overview

A system diagram is a visualization of a System as a flow-chart-like diagram.

A system is indicated by a box. The box marks the boundary of the system and completely contains it. We place a label in the box naming the system.

Since systems transform their inputs into their outputs, we use labelled arrows to represent specific interactions between systems:

• mass transfers are noted with thick arrows;
• energy transfers are noted with thin arrows; and
• information transfers are noted with thin, dashed arrows.

Read more about System Inputs and Outputs and System Interfaces.

Inputs to a system come from other co-systems. Outputs from a system go to other co-systems. However, we are not interested in the details of those co-systems that are outside of the system we are designing. Thus, while we must specify the inputs and outputs, we do not specify the environmental co-systems in the System Diagram.

The input and output flows of systems, and between subsystems, represent System Interfaces. We number each flow; these numbers provide indexing into descriptions of the interfaces themselves. We don’t put interface information directly on the System Diagram to prevent clutter that will confuse other engineers.

Benefits of System Diagrams

Diagrams are "richer" than plain text

As the saying goes, a picture is worth a thousand words. A good diagram can capture a huge amount of information in a very small space. This makes diagrams a dense way to represent information.

Diagrams can also represent non-linear information, such as the multi-dimensional relationships between systems. Text is linear, which prevents it from representing non-linear information efficiently. This makes diagrams easier to both render and understand.

Therefore, diagrams are a richer form of information capture than simple text.

Recording decisions

Each feature of a System Diagram represents at least one decision that was made about the intervention’s design. Thus, diagrams represent records of those decisions.