When we talk about AI,
most discussions focus on:
- Models
- Data
- Algorithms
However, in reality,
AI systems do not operate on models alone.
For AI to function safely in society,
we need:
a structure for decision-making
The Six Core Components of an AI System
An AI system is composed of the following six elements:
- Event
- Signal
- Decision
- Boundary
- Human
- Log
This is:
the blueprint of an AI system
The Fundamental Structure
The architecture of an AI system can be represented as:
Event ↓ Signal ↓ Decision ↓ Boundary ↓ Human / Action ↓ Log
This structure represents:
the decision-making process of AI itself
1. Event
The process begins with:
Event
Examples include:
- User actions
- Transaction data
- Inquiries
- Sensor data
- Logs
AI does not “understand” Events.
AI receives Events as:
input data
In other words:
Events are the raw material of AI systems
2. Signal (AI Model Output)
Next, the AI model produces a:
Signal
Examples include:
- Fraud probability
- Purchase likelihood
- Classification labels
- Generated text
A Signal is:
a prediction made by AI
However, it is critical to understand:
A Signal is NOT a decision
It is merely:
a probabilistic suggestion
3. Decision
Using the Signal,
the system determines what action to take:
Decision
For example:
score > 0.8 → Approve score < 0.2 → Reject otherwise → Escalate to human
This is:
- Business logic
- Decision structure
How AI outputs are used is designed by humans
4. Boundary
The most critical component in an AI system is:
Boundary
Boundary defines:
where AI is allowed to make decisions
Examples include:
- Low confidence
- Unknown data
- High-impact outcomes
- Ethical considerations
- Model disagreement
In these cases:
AI must stop making decisions
And:
hand control back to humans
Boundary is:
the safety mechanism of AI systems
5. Human
In any AI system:
Final responsibility belongs to humans
When a Boundary is triggered,
AI defers the decision to a human.
This means:
Humans are not exception handlers
Humans are the responsible authority
AI systems should not eliminate humans—
they must:
integrate humans into the responsibility structure
6. Log
Finally, we need:
Log
Every decision in an AI system must be recorded:
- Event
- Signal
- Decision
- Boundary activation
- Human judgment
This complete record is:
Decision Trace
Decision Trace Model
AI systems must not only store outcomes,
but also:
the path that led to the decision
That means capturing:
→ Signal
→ Decision
→ Boundary
→ Human
This is known as:
Decision Trace Model
What Decision Trace Enables
With Decision Trace, AI systems can:
- Explain why a decision was made
- Identify root causes of incidents
- Improve decision structures
- Reuse knowledge
In other words:
Decision Trace is a knowledge asset of AI systems
Who Designs AI Systems?
Here is the critical insight:
The quality of an AI system is determined not by the model, but by the decision structure
That means:
The person who designs:
- Event
- Signal
- Decision
- Boundary
- Human
- Log
is:
the true architect of the AI system
The Essence of AI Design
Building an AI system is not about building models.
It is about designing decision structures.
- Event brings in the world
- Signal generates predictions
- Decision determines actions
- Boundary prevents failures
- Human holds responsibility
- Log records decisions
Only when these six elements are in place:
AI becomes a system that can safely operate in society
Final Thought
AI design is not model design.
AI design is the design of decision architecture

AIシステム設計・意思決定構造の設計を専門としています。
Ontology・DSL・Behavior Treeによる判断の外部化、マルチエージェント構築に取り組んでいます。
Specialized in AI system design and decision-making architecture.
Focused on externalizing decision logic using Ontology, DSL, and Behavior Trees, and building multi-agent systems.

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