Turn requirements into an architecture decision and stop before unnecessary complexity.
◷ Estimated reading time: 6 min
A Practical Decision Path
1. Can one model call solve the bounded task?
2. Does the answer need private or current evidence? Add retrieval.
3. Is the execution sequence known? Use a workflow.
4. Must the system choose steps at runtime? Add bounded agentic control.
5. Do independent specialists or organizational boundaries exist? Consider multi-agent.
6. Is an action high impact? Add policy enforcement and human approval.
Pattern Selection Matrix
Requirement
Strong starting pattern
Main trade-off
Bounded generation or extraction
Direct LLM
Limited knowledge and actionability
Private or changing knowledge
RAG
Retrieval quality and freshness
Known business process
Deterministic workflow
Less runtime flexibility
Unknown sequence with tool use
Bounded agentic workflow
Higher evaluation and security surface
Distinct independent specialists
Multi-agent
Handoffs and operational overhead
Irreversible or regulated action
Workflow/agent + HITL
Latency and reviewer capacity
Patterns Compose
An enterprise support system might use RAG for policy evidence, a deterministic workflow for ticket routing, a bounded agent for diagnosis, a skill for refund calculation, and human approval before issuing money. Good architecture does not chase one label; it composes patterns while keeping control boundaries visible.
Architecture Review Questions
What requirement forces each component to exist?
Who controls the next step?
Where is state stored?
What authority can the system exercise?
How does it stop, recover, and escalate?
How will we measure success and failure?
Chapter bridge
Chapter 3 chose the system shape. Chapter 4 asks whether that shape is measurable, secure, and reliable under real variation and attack.
Key Takeaways
Architecture patterns compose; they are not competing product labels.
Every component should be justified by a requirement and paired with evaluation and control.
The most maintainable system keeps knowledge, control, state, and authority boundaries explicit.
A fixed insurance-claim process uses a model to extract fields, then applies deterministic rules and human approval. What is the dominant control pattern?
A research task requires choosing sources and changing direction based on discoveries. Which addition is most justified?
Which statement is most accurate?
What is the best first question in an architecture review?