Glossary
Systems Theory Foundations: This glossary provides formal definitions from systems theory alongside practical guidance for BERT modeling.
Fundamental Concepts
System
Formal Definition: A system is a "thing, a whole entity." More formally, "a system S is a 7-tuple: S = (C, N, G, B, T, H, Δt)" where each element represents components, network, goals, boundary, time, history, and time step.
In BERT: The main system boundary (large circle) that you create as your starting point for analysis.
System Types
Adaptable or Evolvable Systems:
Complex Adaptive Systems (CAS): "Are able to respond to changes in their nominal environmental conditions"
Complex Evolvable Systems (CAES): Can "undergo modifications that permanently change their structures and behaviors to meet the demands of longer-term environmental changes"
In BERT: Use subsystem decomposition to model how different parts of your system adapt to changes.
Component
Definition: "Every object element within the system boundary, including the interfaces, channels, stocks, sensors, and regulators, are components of the system."
In BERT: All elements you place inside your system boundary - subsystems, interfaces, and internal flows.
Component Complexity Types
Simple
Limited number of elements and hierarchy levels
A single coffee machine subsystem
Complex
"Contains many heterogeneous parts and many levels of organization"
Kitchen operations with multiple cooking stations
Complex Adaptive (CAS)
"Ability to change internally to compensate for environmental changes"
Restaurant adapting menu based on supply availability
Complex Adaptive and Evolvable (CAES)
Can make "permanent restructuring in response to long-term environmental alterations"
Restaurant expanding from fast-food to full-service model
Component Properties
Atomic Components: "Leaf nodes in the deconstruction tree" - components not further decomposed because their internal structures are given.
In BERT: When you stop decomposing a subsystem because its internal operation is well-understood or outside your analysis scope.
Member Autonomy (0-1): The degree of autonomy a component has within a system.
Multiset: A component containing "multiple instances of the same kind of element."
In BERT: Multiple identical subsystems (like multiple cashier stations in a restaurant).
Boundary
Definition: "Boundedness constructs effective boundaries to systems."
In BERT: The visual boundary of your main system circle and subsystem circles.
Boundary Properties
Porosity (0-1): The degree to which a boundary allows matter, energy, or messages to pass through it.
In BERT: Represented by the interfaces you place on system boundaries - more interfaces indicate higher porosity.
Perceptive Fuzziness (0-1): The degree of ambiguity in identifying the boundary. Some boundaries are "not easily identifiable enclosures."
Modeling Tip: If you're struggling to define where your system boundary should be, you may be dealing with perceptive fuzziness. Start with a clear core and add boundary elements iteratively.
System Elements
Flow
Definition: A movement of material, energy, or message.
In BERT: The curved arrows you create between elements to represent transfers.
Flow Types by Interaction
Flow
Movement of substance from source to sink
Money flowing from customer to restaurant
Force
Interaction involving push or pull
Regulatory pressure on restaurant operations
Flow Types by Substance
Material
Tangible substance
Food ingredients, dishes, waste
Energy
Flow that does work or can be converted to work
Electricity, heat, human labor
Message
Flow of information or influence
Orders, feedback, regulations
Flow Attributes
In BERT: Edit these in the Properties Panel when you select a flow:
Substance Sub-Type: Specific kind (e.g., "electricity" vs "gravitational potential")
Substance Unit: Unit of measure (e.g., "TONS", "kWh", "$/hour")
Substance Amount: Quantity (e.g., "10/hr")
Parameters: Rate, timing, variance attributes
Flow Outputs
Product: Output that "gives the system its purpose" - the primary valuable output.
In BERT: The main flows exiting through your primary output interfaces.
Waste: Unusable outputs of a process.
In BERT: Secondary flows that represent byproducts or disposal needs.
Interface
Definition: The boundary of a component that receives or sends flows.
In BERT: Small circles placed on system/subsystem boundaries where flows connect.
Protocol: Set of rules governing substance flow into or out of a component.
In BERT: Document protocols in the interface properties or description fields.
Source/Sink (External Entities)
Definition: Sources are the origin of a flow while sinks are the destination.
In BERT: Square elements placed outside your system boundary representing external entities.
Common Source/Sink Types
Source
Provides inputs to system
Suppliers, customers placing orders
Sink
Receives outputs from system
Customers receiving food, waste disposal
Source & Sink
Both provides and receives
Customers (provide money, receive food)
Advanced Concepts
Equivalence
Definition: An equivalence class determined by common criteria among multiple components.
In BERT: Group similar elements to simplify complex models.
Transformation
Definition: "The dynamic behavior of the system of interest" - how inputs are transformed into outputs through differential equations or computer programs.
In BERT: The internal processes within subsystems that convert inputs to outputs.
Implementation: Document transformation rules in subsystem descriptions or link to external process documentation.
Time Elements
Time Unit: The time step over which discrete simulation would operate.
History: Historical records of system behavior, "captured in accounting records" or linked documentation.
In BERT: Reference historical data in system properties or maintain links to time-series data files.
Model Concepts
Model
Definition: A representation of a system that captures essential features for understanding or prediction. Multiple models of a single system can exist at different abstraction levels.
In BERT: Your complete BERT diagram is a model. Use system decomposition to create models at different detail levels.
Disruption
Definition: A change in the environment that impacts system functions.
In BERT: Model disruptions as:
Changes in external entity behavior
New flow requirements
Modified boundary conditions
System adaptations (new subsystems/interfaces)
Quick Reference for BERT Users
Creating Elements Based on Definitions
Start with System: Create main system boundary
Identify Boundaries: Where does your system interact with the environment?
Add Interfaces: Place connection points on boundaries
Connect External Entities: Add sources and sinks outside boundary
Model Flows: Connect entities through interfaces with appropriate substance types
Decompose Components: Break complex subsystems into simpler parts
Document Transformations: Describe how each component processes its inputs
Using Equivalence Classes
Group similar components to reduce model complexity
Use representative subsystems for identical processes
Apply consistent naming conventions for equivalent elements
Managing Complexity
Simple Systems: Few elements, clear hierarchy
Complex Systems: Use hiding (
Hkey) and decomposition strategicallyAdaptive Systems: Model feedback loops and control mechanisms
Evolvable Systems: Plan for structural changes over time
Remember: Every BERT model is a formal system representation. Understanding these theoretical foundations will make your models more rigorous and meaningful.
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