# Application Layer Concepts

> **Audience:** Teams building applications on top of Episteme.
> **Not covered here:** Database internals (see [architecture.md](../../architecture.md)) or implementation roadmap (see [roadmap.md](../../roadmap.md)).

---

## The Boundary Principle

Episteme is a **database engine**. It stores assertions, resolves conflicts via lenses, and serves queries. Everything else is the **application layer**.

### Episteme Owns

| Domain | Responsibilities |
|--------|------------------|
| **Storage** | WAL, KV store, indexes, content-addressing via BLAKE3 |
| **Types** | Assertion, Vote, Epoch, LifecycleStage, MaterializedView |
| **Resolution** | Lenses (Recency, Consensus, Authority, Skeptic, Layered, Constraints) |
| **Query** | Filtering, audit trail, time-travel (`as_of`), decay at resolution time |
| **Integrity** | Ed25519 signature verification, checksums, epoch supersession cascades |
| **API** | HTTP endpoints: `POST /assert`, `POST /vote`, `POST /epoch`, `GET /query` |

### Application Layer Owns

| Domain | Responsibilities |
|--------|------------------|
| **Data Acquisition** | Crawlers, scrapers, API consumers (PubMed, Reddit, FAERS, etc.) |
| **Data Transformation** | NLP extraction, claim identification, confidence assignment |
| **Classification** | Source-class tier assignment, study design classification |
| **Enrichment** | DOI resolution, journal metadata, engagement metrics |
| **Intelligence** | Cluster detection, anomaly detection, signal surfacing |
| **Presentation** | Dashboards, summaries, consumer UX, LLM-powered synthesis |
| **Orchestration** | Agent swarms, reviewers, curators |
| **Client Libraries** | SDKs that wrap the HTTP API (Go, Python, etc.) |
| **Infrastructure** | Key management, budget enforcement, job scheduling |

---

## The Test

For any feature, ask: **"Does this require changes to Episteme's storage, indexing, resolution, or API?"**

- **If yes** → Database feature. It goes in Episteme.
- **If no**, it just calls the API → Application layer. It goes in your app.
- **If both** → Split it. Episteme provides the primitive; your app provides the intelligence.

### Examples

| Feature | DB Primitive | App Intelligence |
|---------|--------------|------------------|
| Source-class decay | Decay formula applied during lens resolution | Which tier a source belongs to |
| Cluster escalation | Accept/store/query escalation assertions | Detect clusters, compute thresholds |
| Disagreement dashboard | Skeptic Lens + conflict_score | UI rendering, LLM summaries |
| Time-travel | `as_of` query parameter | "What changed since you last looked" UX |
| Visual anchoring | Store + query visual_hash | Image hashing, screenshot comparison |
| Pharma data | Ingest via `POST /assert` | Crawl PubMed, extract claims, classify |

---

## Core Application Components

These are the building blocks that most Episteme-powered applications need.

### 1. Ingestion Pipeline

Transforms raw source material into signed assertions.

```
[Raw Source] → [Crawler/API] → [NLP Extraction] → [Classification] → [Enrichment] → [Signing] → [POST /assert]
```

**Responsibilities:**
- Fetch documents from source systems (PubMed API, Reddit API, web scraping)
- Extract claims as subject/predicate/object triples
- Assign confidence based on extraction quality
- Classify source tier (0-6)
- Enrich with structured metadata
- Sign with agent key
- Submit to Episteme

**See:** [Consumer Health Ingestion](./consumer-health.md#ingestion-pipeline)

### 2. Source-Class Classifier

Determines the authority tier of each source.

| Tier | Source Type | Examples |
|------|-------------|----------|
| 0 | Regulatory action | FDA label change, EMA withdrawal |
| 1 | Peer-reviewed RCT, meta-analysis | NEJM, Lancet, JAMA |
| 2 | Observational study, real-world evidence | Insurance claims, EHR studies |
| 3 | Pharmacovigilance | FAERS reports, EudraVigilance |
| 4 | Clinician anecdote, case report | Conference presentations, case series |
| 5 | Patient community | Reddit, forums, patient registries |
| 6 | Media, influencer, commercial | TikTok, news articles, pharma marketing |

**Implementation:** Rule-based classifier or ML model that maps source metadata (URL pattern, DOI prefix, platform) to tier.

**Domain-specific:** The tier map for pharma differs from finance differs from legal.

### 3. Background Gardener

Monitors the knowledge graph for signals that warrant attention.

**Responsibilities:**
- Query assertion counts by subject/predicate/tier
- Detect unusual clustering (e.g., 1,847 Tier-5 assertions in 6 months)
- Generate escalation assertions when thresholds are crossed
- Trigger TrustRank decay on schedule
- Update agent reputations based on outcomes

**Episteme primitives it uses:**
- `GET /query` with aggregation
- `POST /assert` for escalation assertions
- `POST /admin/decay-trust-ranks` for scheduled decay

### 4. Presentation Layer

Renders Episteme query results for end users.

**Options:**
- **Dashboard:** React/Vue app that visualizes conflict scores, tier positions, timelines
- **API Gateway:** REST/GraphQL layer that adds business logic before returning data
- **Chat Interface:** LLM-powered conversational access to the knowledge graph
- **Reports:** Scheduled exports (PDF, email digests)

**Episteme primitives it uses:**
- `GET /query` with various lenses
- Layered Consensus for per-tier breakdown
- Skeptic Lens for disagreement surfacing
- `as_of` for time-travel views
- `since` for change tracking

### 5. Agent Integration

Connects AI agents to Episteme for reading and writing knowledge.

**ADK-Go Tool Example:**
```go
// Tool: Query the knowledge graph
func QueryKnowledge(ctx context.Context, subject, predicate string, lens string) (string, error) {
    resp, err := episteme.Query(ctx, &QueryParams{
        Subject:   subject,
        Predicate: predicate,
        Lens:      lens,
    })
    if err != nil {
        return "", err
    }
    return formatForAgent(resp), nil
}

// Tool: Assert a new fact
func AssertFact(ctx context.Context, subject, predicate, object string, confidence float32) error {
    return episteme.Assert(ctx, &AssertionRequest{
        Subject:    subject,
        Predicate:  predicate,
        Object:     ObjectText(object),
        Confidence: confidence,
        Lifecycle:  "Proposed",
    })
}
```

**See:** [ADK-Go Integration Guide](../../.claude/guides/integrations/adk-go-episteme.md)

---

## Vertical-Specific Guides

| Vertical | Guide | Key Components |
|----------|-------|----------------|
| **Consumer Health** | [consumer-health.md](./consumer-health.md) | Pharma crawlers, tier classification, disagreement dashboard |
| **Financial Due Diligence** | (planned) | SEC filings, analyst extraction, invalidation cascades |
| **Agile Agent Team** | (planned) | Constraints lens, lifecycle workflow, audit trail |

---

## Quick Reference: What Goes Where

| If you need to... | Episteme provides... | You build... |
|-------------------|---------------------|--------------|
| Store conflicting facts | Assertion type, append-only DAG | Nothing — just POST assertions |
| Resolve conflicts | Lenses (Recency, Consensus, Skeptic, Layered) | Lens selection logic |
| Query historical state | `as_of` parameter | Time-travel UI |
| Track changes | `since` parameter + MV changelog | Notification system |
| Weight by source authority | `source_class` field + source-aware decay | Tier classifier |
| Detect emerging signals | Skeptic Lens + conflict_score | Gardener (threshold logic) |
| Show per-tier consensus | Layered Consensus Lens | Dashboard UI |
| Extract claims from papers | Nothing — pre-assertion transform | NLP pipeline |
| Sign assertions | Signature verification | Agent wallet / key management |
| Generate summaries | Structured query responses | LLM summarizer |

---

## See Also

- [Architecture](../../architecture.md) — Database internals
- [Roadmap](../../roadmap.md) — What's implemented vs planned
- [API Reference](../../ai-lookup/services/) — Endpoint documentation
- [Use Cases](../../use-cases/) — Full scenario walkthroughs