> For the complete documentation index, see [llms.txt](https://bert.gitbook.io/bert-documentation/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://bert.gitbook.io/bert-documentation/getting-started/creating-your-first-system/step-8-traverse-the-boundary.md).

# Step 8: Traverse The Boundary

## Does Your System Make Sense?

You've now mapped your system's key flows - primary output, waste, and inputs - along with their interfaces and sources/sinks. Time to step back and validate: does this tell a coherent story about how your system works?

## Review Your Flow Logic

Look at your complete model and ask these critical questions:

**Input-Output Balance**: Do your inputs provide what's needed to create your outputs?

**Examples from our model library:**

* **Cell**: Glucose + Oxygen → Energy + CO2 + Water ✓
* **Ecosystem**: Sunlight + Nutrients → Biomass + Dead matter ✓
* **Solar Panel**: Solar radiation → Electricity + Heat ✓
* **Organization**: Materials + Labor → Products + Overhead ✓
* **LLM**: Prompts + Training data → Generated text + Computational heat ✓

**Interface Consistency**: Do your interfaces make sense for the flows they handle?

* Are input interfaces designed to receive what your sources provide?
* Are output interfaces designed to deliver what your sinks need?

**Waste Accounting**: Does your waste make logical sense given your inputs and processes?

## Validation Questions

**Energy/Resource Conservation**: Where does the energy/matter come from and go to?

**Purpose Alignment**: Do your inputs support creating your primary output?

**Environmental Fit**: Do your sources and sinks exist in the same environment as your system?

**Missing Elements**: Are there obvious inputs or outputs you haven't accounted for?

## What to Look For

**Red flags that suggest revision needed:**

* Outputs that require inputs you haven't identified
* Interfaces that don't match their flows
* Sources/sinks that seem disconnected from your system's environment
* Imbalanced resource accounting (more output than input, or vice versa)

**Good signs your model is coherent:**

* Clear transformation story from inputs to outputs
* Interfaces that make sense for their context
* Balanced resource accounting
* All flows have logical sources and destinations

## Preparing for Internal Analysis

Once your input-output story makes sense, you're ready to look inside your system and understand how it actually transforms inputs into outputs through internal processes and subsystems.

A valid system model tells a believable story about transformation - how inputs become outputs through the system's processes, with waste as a natural byproduct. If your story has gaps, revisit your flows before proceeding to internal analysis.


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