# Glossary

## Core Terms

**System** - The main thing you're analyzing (large circle in BERT)

**Subsystem** - A component inside your system (smaller circles inside the system)

**Boundary** - The edge between your system and its environment (gray ring around system)

**Environment** - Everything outside your system that interacts with it

**Interface** - Connection point where your system meets the environment (rectangles on boundary)

## Flows and Connections

**Flow** - Transfer of material, energy, or information between elements (arrow lines)

**Source** - External entity that provides inputs to your system (square outside system)

**Sink** - External entity that receives outputs from your system (square outside system)

**Resource** - Useful input your system needs to function

**Product** - Primary valuable output your system creates

**Waste** - Byproducts or unusable outputs from your system

## Flow Types

**Material** - Physical substances (food, parts, documents)

**Energy** - Power, heat, or work (electricity, fuel, labor)

**Information** - Data, signals, or messages (orders, feedback, instructions)

## System Properties

**Complexity** - How your system behaves:

* Simple: Predictable, fixed behavior
* Adaptive: Responds to environmental changes
* Evolvable: Can restructure itself permanently

**Equivalence** - Component type classification (what kind of thing it is)

**Protocol** - Rules governing how an interface operates

**Porosity** - How open a boundary is to flows passing through

## Analysis Concepts

**Decomposition** - Breaking a system into subsystems for deeper analysis

**Recursive Analysis** - Treating any subsystem as a new system to analyze

**Transformation** - How a system converts inputs into outputs

**Model** - Your BERT diagram representing the system

## Practical Examples

| BERT Element  | Real-World Example |
| ------------- | ------------------ |
| System        | Restaurant         |
| Subsystem     | Kitchen            |
| Interface     | Order counter      |
| Source        | Food supplier      |
| Sink          | Customer           |
| Product flow  | Prepared meals     |
| Waste flow    | Food scraps        |
| Resource flow | Raw ingredients    |

***

Need more detail? See the [11-step tutorial](/bert-documentation/getting-started/creating-your-first-system.md) for hands-on practice with these concepts.


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