diff --git a/docs/design/adr/ADR-011-Four-Layer-Data-Architecture.md b/docs/design/adr/ADR-011-Four-Layer-Data-Architecture.md
new file mode 100644
index 000000000..7e603f7cd
--- /dev/null
+++ b/docs/design/adr/ADR-011-Four-Layer-Data-Architecture.md
@@ -0,0 +1,67 @@
+# ADR-011: Four-Layer Data Architecture
+
+## Status
+Accepted
+
+## Context
+We need a clear separation between raw data, extracted knowledge, and decision intelligence to avoid building expensive, tightly-coupled AI systems.
+
+## Decision
+Separate into four layers:
+
+### Layer 1: Raw Archive (cheap, immutable)
+- Original files never changed
+- Hash guarantees integrity
+- Storage policy: active (30 days) → archive (long-term, cheaper)
+
+### Layer 2: Knowledge Extraction
+- Objects, geometry, GPS, classifications, bounding boxes, embeddings
+- Observations and Evidence created
+- Structured knowledge used for most queries, not video files
+
+### Layer 3: Knowledge Graph / Ontology
+- Road A12 → has Observation → Crack → belongs to Area → Stockholm
+- Answers: "Show all main roads where cracking increased last 12 months"
+- Comes from knowledge graph, not by reading video files
+
+### Layer 4: Decision Intelligence
+- Verified Decision Cases
+- Curated datasets for AI training
+- Business impact tracking
+
+## Key Principles
+
+1. **Archive Artifact** = Original file, never modified
+2. **Knowledge Artifact** = Extracted knowledge, can be re-generated
+3. **Ontology before model** — taxonomy answers "what does it mean in our domain?"
+4. **AI models trained on curated datasets**, not whole archive
+
+## Data Lifecycle
+
+```
+Upload → Immutable Archive → Metadata Extraction → Knowledge Extraction
+→ Ontology Mapping → Decision Pipeline → Learning → Archive Retention
+```
+
+Each step produces a new Artifact with version history.
+
+## Long-term Goal
+
+"Every real observation is converted once to structured knowledge and can then be reused infinitely for analysis, decision support, history, training, and future AI models."
+
+## Consequences
+
+### Positive
+- Raw data = revisionable archive
+- Real product = growing knowledge base + verified Decision Cases
+- Can swap AI models without losing originals
+- Cheaper storage (archive vs active)
+
+### Negative
+- More complex pipeline
+- Need to manage extraction models
+- Knowledge graph maintenance
+
+## Related
+- ADR-002: Artifact is common base contract
+- ADR-003: Event Sourcing for traceability
diff --git a/packages/domain/src/artifacts/archive-artifact.ts b/packages/domain/src/artifacts/archive-artifact.ts
new file mode 100644
index 000000000..5c4e7e8ce
--- /dev/null
+++ b/packages/domain/src/artifacts/archive-artifact.ts
@@ -0,0 +1,68 @@
+/**
+ * Archive Artifact — Immutable Original
+ *
+ * Principle: Original files never change.
+ * Hash guarantees integrity.
+ * Storage policy: active → archive (cheaper long-term).
+ *
+ * ADR-011: Four-Layer Data Architecture
+ * Layer 1: Raw Archive (this file)
+ */
+
+import { ArtifactId } from '../common/ids';
+import { Hash, StorageUri } from '../common/value-objects';
+
+export interface ArchiveArtifact {
+  readonly id: ArtifactId;
+  readonly originalName: string;
+  readonly mimeType: string;
+  readonly sizeBytes: number;
+  readonly hash: Hash;
+  readonly storageUri: StorageUri;
+  readonly exif?: {
+    readonly device?: string;
+    readonly gpsLat?: number;
+    readonly gpsLng?: number;
+    readonly timestamp?: Date;
+    readonly iso?: number;
+    readonly exposure?: string;
+    readonly focalLength?: string;
+  };
+  readonly uploadedAt: Date;
+  readonly uploadedBy: string;
+  readonly retentionPolicy: 'active' | 'archive';
+  readonly archiveAfterDate?: Date;
+}
+
+export interface CreateArchiveArtifactParams {
+  readonly id: ArtifactId;
+  readonly originalName: string;
+  readonly mimeType: string;
+  readonly sizeBytes: number;
+  readonly hash: Hash;
+  readonly storageUri: StorageUri;
+  readonly exif?: ArchiveArtifact['exif'];
+  readonly uploadedBy: string;
+  readonly retentionPolicy?: 'active' | 'archive';
+}
+
+export class ArchiveArtifactFactory {
+  static create(params: CreateArchiveArtifactParams): ArchiveArtifact {
+    return {
+      ...params,
+      retentionPolicy: params.retentionPolicy ?? 'active',
+      archiveAfterDate: params.retentionPolicy === 'archive'
+        ? undefined
+        : new Date(Date.now() + 30 * 24 * 60 * 60 * 1000), // 30 days default
+      uploadedAt: new Date(),
+    };
+  }
+
+  static archive(artifact: ArchiveArtifact): ArchiveArtifact {
+    return {
+      ...artifact,
+      retentionPolicy: 'archive',
+      archiveAfterDate: undefined,
+    };
+  }
+}
diff --git a/packages/domain/src/artifacts/data-lifecycle.ts b/packages/domain/src/artifacts/data-lifecycle.ts
new file mode 100644
index 000000000..d49803448
--- /dev/null
+++ b/packages/domain/src/artifacts/data-lifecycle.ts
@@ -0,0 +1,52 @@
+/**
+ * Data Lifecycle — From Reality to Decision
+ *
+ * ADR-011: Four-Layer Data Architecture
+ *
+ * Flow:
+ * Reality (phone, video, images)
+ *   ↓
+ * Raw Archive (immutable)
+ *   ↓
+ * Knowledge Extraction
+ *   ↓
+ * Knowledge Graph / Ontology
+ *   ↓
+ * Decision Intelligence
+ *
+ * Each step produces a new Artifact with its own version history.
+ */
+
+import { ArchiveArtifact } from './archive-artifact';
+import { KnowledgeArtifact } from './knowledge-artifact';
+
+export interface DataLifecycleStep {
+  readonly step: 'upload' | 'archive' | 'extract_metadata' | 'extract_knowledge' | 'ontology_map' | 'decision' | 'learn' | 'retain';
+  readonly inputArtifactIds: string[];
+  readonly outputArtifactIds: string[];
+  readonly timestamp: Date;
+  readonly processor: string; // Model, human, or system
+}
+
+export interface DataLifecycle {
+  readonly archiveArtifact: ArchiveArtifact;
+  readonly knowledgeArtifacts: KnowledgeArtifact[];
+  readonly steps: DataLifecycleStep[];
+}
+
+export const DataLifecycleRules = {
+  // Original never changes
+  immutableArchive: (archive: ArchiveArtifact): boolean => {
+    return archive.hash !== undefined && archive.hash.value.length > 0;
+  },
+
+  // Knowledge can be re-extracted without touching archive
+  reextractable: (lifecycle: DataLifecycle): boolean => {
+    return lifecycle.archiveArtifact !== undefined;
+  },
+
+  // Every step produces artifacts
+  artifactAtEveryStep: (lifecycle: DataLifecycle): boolean => {
+    return lifecycle.steps.every(step => step.outputArtifactIds.length > 0);
+  },
+} as const;
diff --git a/packages/domain/src/artifacts/knowledge-artifact.ts b/packages/domain/src/artifacts/knowledge-artifact.ts
new file mode 100644
index 000000000..280ce138a
--- /dev/null
+++ b/packages/domain/src/artifacts/knowledge-artifact.ts
@@ -0,0 +1,60 @@
+/**
+ * Knowledge Artifact — Extracted Knowledge
+ *
+ * Principle: Structured knowledge is the real product.
+ * Raw data becomes knowledge once, then reused infinitely.
+ *
+ * ADR-011: Four-Layer Data Architecture
+ * Layer 2: Knowledge Extraction (this file)
+ */
+
+import { ArtifactId, ObservationId } from '../common/ids';
+import { Hash, StorageUri, GeoLocation } from '../common/value-objects';
+
+export interface KnowledgeArtifact {
+  readonly id: ArtifactId;
+  readonly sourceArchiveId: ArtifactId; // Links to original
+  readonly type: 'observation' | 'segmentation' | 'classification' | 'feature_vector' | 'relation';
+  readonly extractedAt: Date;
+  readonly extractedBy: string; // Model or human
+  readonly confidence: number; // 0.0 to 1.0
+  readonly data: unknown; // Type-specific data
+  readonly hash: Hash;
+  readonly storageUri: StorageUri;
+  readonly lineage: ArtifactId[];
+}
+
+// Specific knowledge types
+export interface ObservationKnowledge {
+  readonly observationId: ObservationId;
+  readonly description: string;
+  readonly location: GeoLocation;
+  readonly boundingBox?: {
+    readonly x: number;
+    readonly y: number;
+    readonly width: number;
+    readonly height: number;
+  };
+  readonly classifications: string[]; // Taxonomy references
+  readonly qualityScore: number;
+}
+
+export interface SegmentationKnowledge {
+  readonly maskUri: string;
+  readonly objectClass: string;
+  readonly pixelCount: number;
+  readonly areaMeters: number;
+}
+
+export interface FeatureVectorKnowledge {
+  readonly dimensions: number;
+  readonly vector: number[];
+  readonly modelVersion: string;
+}
+
+export interface RelationKnowledge {
+  readonly subjectId: string;
+  readonly predicate: string;
+  readonly objectId: string;
+  readonly confidence: number;
+}
diff --git a/packages/domain/src/index.ts b/packages/domain/src/index.ts
index 4c1a48f2d..9c3ef12d3 100644
--- a/packages/domain/src/index.ts
+++ b/packages/domain/src/index.ts
@@ -44,6 +44,27 @@ export {
   Severity,
   PriorityValue,
 } from './common/value-objects';
+
+// Four-Layer Data Architecture
+export {
+  ArchiveArtifact,
+  CreateArchiveArtifactParams,
+  ArchiveArtifactFactory,
+} from './artifacts/archive-artifact';
+
+export {
+  KnowledgeArtifact,
+  ObservationKnowledge,
+  SegmentationKnowledge,
+  FeatureVectorKnowledge,
+  RelationKnowledge,
+} from './artifacts/knowledge-artifact';
+
+export {
+  DataLifecycle,
+  DataLifecycleStep,
+  DataLifecycleRules,
+} from './artifacts/data-lifecycle';
 export * from './common/enums';
 export * from './common/errors';