
Pattern Abstract Grammar
Structured Instructions for AI Systems
Validation Gates
Validation gates are checkpoints that verify conditions before proceeding. They provide structure for the AI to confirm requirements are met.
Gate Structureα
Each validation gate contains one or more check items with optional evidence and failure actions.
Gate StructureVALIDATION GATE: ✅ file_exists("config.json") ✅ schema_valid(config, CONFIG_SCHEMA) ✅ dependencies_resolved IF FAIL: REPORT "Validation failed" EXIT 1
Check Markersβ
| Marker | Meaning | Usage |
|---|---|---|
✅ | Success check | Visual verification point |
ASSERT | Hard assertion | ASSERT condition |
REQUIRE | Prerequisite | REQUIRE dependency |
[high] | Priority high | Critical validation |
[medium] | Priority medium | Standard validation |
[low] | Priority low | Optional validation |
Phase Transition Rulesγ
Gates guide phase progression. The AI should verify all gates pass before moving to the next phase.
- Phase N should complete before proceeding to Phase N+1
- All ✅ markers should evaluate to true
- IF FAIL actions indicate what to do on gate failure
- Task markers track progress: [ ] pending, [x] complete, [>] in progress
Writing Effective Conditionsδ
Gate conditions should be specific and concrete rather than vague and subjective. Specific conditions give the model clearer patterns to follow.
| Quality | Example | Why |
|---|---|---|
Specific | customer_email matches email_pattern | Concrete pattern to check |
Specific | record_count > 0 | Clear numeric comparison |
Specific | all required_fields present | Defined existence check |
Vague | email looks valid | Subjective interpretation |
Vague | data is good | Undefined criteria |
Vague | everything worked | Unclear scope |
Limitations
Understanding PAG's boundaries helps set appropriate expectations for both individual documents and multi-agent orchestrations.
Known Boundariesε
PAG provides structured guidance but operates within inherent constraints of LLM-based systems:
No Runtime Execution
PAG documents are instructions, not executable code:
- The LLM reads instructions and uses its available tools
- PAG describes what to do, not how the LLM processes it
- No guarantee the LLM will follow every instruction precisely
No Confidence Introspection
PAG cannot query model internal states:
- Validation gates check outcomes, not prediction certainty
- No way to say "only proceed if confidence > 90%"
- Gates verify observable conditions only
Probabilistic Output
LLM outputs are inherently variable:
- Same document may produce different results across invocations
- PAG provides structure but cannot guarantee determinism
- Critical operations should include verification steps
Context Window Constraints
Token limits affect document size:
- Complex documents may need chunking or summarization
- Handoff signals pass summary context, not full history
- Long workflows may lose early context without preservation
Sequential Agent Execution
Agents execute one at a time:
- Each agent must complete before the next begins
- DAG patterns express parallelism but depend on tooling
- Long orchestrations have cumulative latency
No Cross-Session State
State doesn't persist automatically:
- Workflow state must be explicitly written to documents
- Resumption requires reading workflow-state file
- Design with checkpoint awareness
Tool Availability Dependency
PAG assumes tools are available:
- EXECUTE Task requires Task tool in agent's toolset
- File operations require Read, Write, Edit tools
- Agent capabilities vary — PAG cannot guarantee availability
No Feedback Loops
PAG describes linear or branching flows:
- Agents cannot "watch" for changes in real-time
- Iteration requires explicit FOR EACH structures
- WHEN blocks require tool support for event handling