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+# Story 8: External Dependencies Management
+
+## Story Overview
+
+**As an** application manager  
+**I want** to track external dependencies for applications  
+**So that** I can document and manage all external services, databases, and resources my applications rely on
+
+**Story Type**: Feature (Core Domain)  
+**Priority**: High  
+**Estimated Effort**: 5-7 days  
+**Dependencies**: Story 2 (Applications)
+
+---
+
+## Business Value
+
+External dependencies represent critical integrations and resources that applications rely on. This enables:
+- Complete visibility of application dependencies
+- Risk assessment and impact analysis
+- Dependency lifecycle tracking
+- Foundation for data usage agreement management
+- Network and security planning
+
+---
+
+## Scope
+
+### In Scope
+✅ External dependency CRUD operations  
+✅ Dependency type management (catalog)  
+✅ Dependency-Application association  
+✅ Validity period tracking (start/end dates)  
+✅ Dependency documentation and metadata  
+✅ Filtering and search capabilities  
+
+### Out of Scope
+❌ Data Usage Agreement associations (Story 9)  
+❌ Automated dependency detection  
+❌ Dependency health monitoring  
+❌ Automated alerts for expiring dependencies  
+
+---
+
+## Database Schema
+
+```sql
+-- Dependency Types Catalog
+CREATE TABLE dependency_type (
+    id UUID PRIMARY KEY,
+    type_name VARCHAR(100) UNIQUE NOT NULL,
+    description TEXT,
+    created_at TIMESTAMP NOT NULL,
+    updated_at TIMESTAMP NOT NULL
+);
+
+-- External Dependencies
+CREATE TABLE external_dependency (
+    id UUID PRIMARY KEY,
+    application_id UUID NOT NULL REFERENCES application(id) ON DELETE CASCADE,
+    dependency_type_id UUID NOT NULL REFERENCES dependency_type(id),
+    name VARCHAR(255) NOT NULL,
+    description TEXT,
+    technical_documentation TEXT,
+    validity_start_date DATE,
+    validity_end_date DATE,
+    created_at TIMESTAMP NOT NULL,
+    updated_at TIMESTAMP NOT NULL,
+    CONSTRAINT fk_dependency_application FOREIGN KEY (application_id) REFERENCES application(id),
+    CONSTRAINT fk_dependency_type FOREIGN KEY (dependency_type_id) REFERENCES dependency_type(id),
+    CONSTRAINT check_validity_dates CHECK (validity_end_date IS NULL OR validity_end_date >= validity_start_date)
+);
+
+-- Indexes
+CREATE INDEX idx_ext_dep_application ON external_dependency(application_id);
+CREATE INDEX idx_ext_dep_type ON external_dependency(dependency_type_id);
+CREATE INDEX idx_ext_dep_validity_end ON external_dependency(validity_end_date);
+CREATE INDEX idx_ext_dep_name ON external_dependency(name);
+
+-- Insert default dependency types
+INSERT INTO dependency_type (id, type_name, description, created_at, updated_at) VALUES
+    (uuid_generate_v4(), 'WEB_SERVICE', 'REST APIs, SOAP services, microservices', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP),
+    (uuid_generate_v4(), 'DATABASE', 'External database connections', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP),
+    (uuid_generate_v4(), 'CERTIFICATE', 'SSL/TLS certificates, authentication certificates', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP),
+    (uuid_generate_v4(), 'NETWORK_FLOW', 'Network connections, firewall rules, VPN tunnels', CURRENT_TIMESTAMP, CURRENT_TIMESTAMP);
+```
+
+---
+
+## Key Business Logic
+
+### Validity Period Management
+- **Validity Start Date**: When the dependency becomes available/authorized for use
+- **Validity End Date**: When the dependency expires (optional for indefinite dependencies)
+- **Active Status**: A dependency is considered "active" if:
+  - Current date >= validity_start_date (or no start date)
+  - Current date <= validity_end_date (or no end date)
+
+### Expiration Tracking
+- Dependencies approaching expiration (within 30 days) should be highlighted
+- Expired dependencies (end date in the past) should be flagged
+- No validation prevents using expired dependencies (warning only)
+
+---
+
+## Key Endpoints
+
+### Dependency Types (Catalog)
+- `GET /api/dependency-types` - List all dependency types
+- `GET /api/dependency-types/{id}` - Get dependency type by ID
+- `POST /api/dependency-types` - Create custom dependency type (admin only)
+- `PUT /api/dependency-types/{id}` - Update dependency type (admin only)
+- `DELETE /api/dependency-types/{id}` - Delete dependency type (admin only, if unused)
+
+### External Dependencies
+- `GET /api/applications/{appId}/dependencies` - List dependencies for application
+- `GET /api/dependencies` - List all dependencies (paginated, filtered)
+- `GET /api/dependencies/{id}` - Get dependency details
+- `POST /api/applications/{appId}/dependencies` - Create dependency
+- `PUT /api/dependencies/{id}` - Update dependency
+- `DELETE /api/dependencies/{id}` - Delete dependency
+- `GET /api/dependencies/expiring?days={30}` - Get dependencies expiring soon
+- `GET /api/dependencies/expired` - Get expired dependencies
+- `GET /api/dependencies/by-type/{typeId}` - Filter by dependency type
+
+---
+
+## DTOs
+
+```typescript
+export interface DependencyType {
+  id: string;
+  typeName: string;
+  description?: string;
+  createdAt: Date;
+  updatedAt: Date;
+}
+
+export interface ExternalDependency {
+  id: string;
+  application: { id: string; name: string };
+  dependencyType: DependencyType;
+  name: string;
+  description?: string;
+  technicalDocumentation?: string;
+  validityStartDate?: Date;
+  validityEndDate?: Date;
+  isActive: boolean; // Computed based on validity dates
+  daysUntilExpiration?: number; // Computed if expiring soon
+  createdAt: Date;
+  updatedAt: Date;
+}
+
+export interface CreateExternalDependencyRequest {
+  dependencyTypeId: string;
+  name: string;
+  description?: string;
+  technicalDocumentation?: string;
+  validityStartDate?: Date;
+  validityEndDate?: Date;
+}
+
+export interface UpdateExternalDependencyRequest {
+  dependencyTypeId?: string;
+  name?: string;
+  description?: string;
+  technicalDocumentation?: string;
+  validityStartDate?: Date;
+  validityEndDate?: Date;
+}
+
+export interface CreateDependencyTypeRequest {
+  typeName: string;
+  description?: string;
+}
+```
+
+---
+
+## Frontend Components
+
+### DependencyTypeManagementComponent (Admin Only)
+- Table view of all dependency types
+- CRUD operations for custom types
+- Default types (WEB_SERVICE, DATABASE, CERTIFICATE, NETWORK_FLOW) cannot be deleted
+- Validation: Cannot delete type if dependencies exist
+
+### DependencyListComponent (Application Detail Tab)
+- Displayed as tab in Application Detail view
+- Table columns: Name, Type, Status (Active/Expiring/Expired), Validity Period, Actions
+- Status indicators:
+  - **Active**: Green badge (current date within validity period)
+  - **Expiring Soon**: Yellow badge (expires within 30 days)
+  - **Expired**: Red badge (end date in past)
+  - **Not Yet Valid**: Gray badge (start date in future)
+- Filter by:
+  - Dependency type
+  - Status (all, active, expiring, expired)
+- Sort by name, type, expiration date
+- "Add Dependency" button
+- Actions: View, Edit, Delete
+
+### DependencyFormComponent
+- Modal or inline form
+- Fields:
+  - **Dependency Type** (required, dropdown from catalog)
+  - **Name** (required, text input)
+  - **Description** (optional, textarea)
+  - **Technical Documentation** (optional, textarea or rich text)
+  - **Validity Start Date** (optional, date picker)
+  - **Validity End Date** (optional, date picker)
+- Validation:
+  - Name required
+  - Dependency type required
+  - End date must be >= start date
+  - Show warning if end date is in the past
+  - Show warning if end date is within 30 days
+- Support both create and edit modes
+
+### DependencyDetailComponent
+- Display full dependency details
+- Show status badge (active/expiring/expired)
+- Show computed fields:
+  - "Days until expiration" if expiring soon
+  - "Expired X days ago" if expired
+- Show technical documentation (formatted)
+- "Edit" and "Delete" buttons
+- Link to application
+- Future: Link to data usage agreements (Story 9)
+
+### ExpiringDependenciesWidget (Dashboard)
+- Widget showing dependencies expiring within 30 days
+- Sortable by expiration date
+- Click to navigate to dependency detail
+- Badge showing count of expiring dependencies
+
+---
+
+## Acceptance Criteria
+
+### Backend
+- [ ] Dependency types can be listed
+- [ ] Admin can create custom dependency types
+- [ ] Default dependency types are seeded in database
+- [ ] Dependency type cannot be deleted if dependencies exist
+- [ ] External dependency can be created for an application
+- [ ] Dependency creation validates application exists
+- [ ] Dependency creation validates dependency type exists
+- [ ] Validity dates are validated (end >= start)
+- [ ] Dependencies can be updated
+- [ ] Dependencies can be deleted
+- [ ] Dependencies can be listed per application
+- [ ] Dependencies can be filtered by type
+- [ ] Dependencies can be filtered by status (active/expiring/expired)
+- [ ] Expiring dependencies query returns correct results
+- [ ] Active status is computed correctly
+- [ ] Days until expiration is computed correctly
+- [ ] All endpoints authenticated
+- [ ] Tests pass (>80% coverage)
+
+### Frontend
+- [ ] User can view list of dependencies for an application
+- [ ] Dependencies show status badge (active/expiring/expired)
+- [ ] User can filter dependencies by type
+- [ ] User can filter dependencies by status
+- [ ] User can create new dependency
+- [ ] Form validates all required fields
+- [ ] Form validates date logic (end >= start)
+- [ ] Form shows warnings for past or soon expiring dates
+- [ ] User can view dependency details
+- [ ] User can edit existing dependency
+- [ ] User can delete dependency (with confirmation)
+- [ ] Expiring dependencies are highlighted
+- [ ] Admin can manage dependency types catalog
+- [ ] Success/error notifications displayed
+- [ ] Tests pass (>70% coverage)
+
+---
+
+## Testing Scenarios
+
+### Scenario 1: Create External Dependency
+1. Navigate to Application Detail → Dependencies tab
+2. Click "Add Dependency"
+3. Fill in form:
+   - Type: "WEB_SERVICE"
+   - Name: "Payment Gateway API"
+   - Description: "External payment processing service"
+   - Technical Documentation: "Endpoint: https://api.payment.com/v2"
+   - Validity Start: 2026-01-01
+   - Validity End: 2027-12-31
+4. Click "Save"
+5. Verify success notification
+6. Verify dependency appears in list with "Active" status (green badge)
+
+### Scenario 2: Expiring Dependency Warning
+1. Navigate to Application Detail → Dependencies tab
+2. Click "Add Dependency"
+3. Fill in form with end date 20 days from today
+4. Verify warning message: "This dependency expires in 20 days"
+5. Save dependency
+6. Verify dependency shows "Expiring Soon" badge (yellow)
+
+### Scenario 3: Expired Dependency
+1. Navigate to Application Detail → Dependencies tab
+2. Click "Add Dependency"
+3. Fill in form with end date in the past
+4. Verify warning message: "This dependency has already expired"
+5. Save dependency (system allows but warns)
+6. Verify dependency shows "Expired" badge (red)
+
+### Scenario 4: Date Validation
+1. Create dependency form
+2. Set start date: 2027-01-01
+3. Set end date: 2026-01-01 (before start)
+4. Attempt to save
+5. Verify error: "End date must be after start date"
+
+### Scenario 5: Filter Dependencies
+1. Navigate to Application Detail → Dependencies tab
+2. Create dependencies of different types
+3. Filter by type: "DATABASE"
+4. Verify only database dependencies shown
+5. Filter by status: "Expiring"
+6. Verify only expiring dependencies shown
+
+### Scenario 6: Manage Dependency Types (Admin)
+1. Login as admin
+2. Navigate to Settings → Dependency Types
+3. Click "Create Custom Type"
+4. Name: "CLOUD_SERVICE"
+5. Description: "Cloud service providers and SaaS platforms"
+6. Save
+7. Verify new type appears in catalog
+8. Verify new type available in dependency creation form
+
+### Scenario 7: Delete Dependency Type Protection
+1. Login as admin
+2. Navigate to Settings → Dependency Types
+3. Attempt to delete "WEB_SERVICE" (has dependencies)
+4. Verify error: "Cannot delete dependency type with existing dependencies"
+5. Create new unused type
+6. Delete it
+7. Verify successful deletion
+
+### Scenario 8: View Expiring Dependencies Dashboard
+1. Navigate to main dashboard
+2. View "Expiring Dependencies" widget
+3. Verify list shows dependencies expiring within 30 days
+4. Verify sorted by expiration date (soonest first)
+5. Click on dependency
+6. Verify navigation to dependency detail
+
+---
+
+## Integration Points
+
+### Application Detail Enhancement
+Add "Dependencies" tab showing:
+- List of all external dependencies
+- Status overview (count by status)
+- "Add Dependency" button
+- Filter and search controls
+
+### Dashboard Enhancement (Optional for Story 8)
+Add widget showing:
+- Expiring dependencies count
+- Top 5 dependencies expiring soonest
+- Link to full list
+
+---
+
+## Performance Considerations
+
+- [ ] Index on application_id for fast dependency lookup per application
+- [ ] Index on validity_end_date for expiring/expired queries
+- [ ] Index on dependency_type_id for type filtering
+- [ ] Compute active status and days until expiration in service layer (not stored)
+- [ ] Pagination for dependency lists (can grow large)
+
+---
+
+## Future Enhancements (Phase 3)
+
+- [ ] Automated dependency scanning/detection
+- [ ] Dependency health monitoring
+- [ ] Automated email alerts for expiring dependencies
+- [ ] Dependency impact analysis (which apps depend on this service)
+- [ ] Dependency renewal workflow
+- [ ] Integration with certificate management tools
+- [ ] Network diagram visualization
+- [ ] Bulk import of dependencies from CSV
+
+---
+
+**Story Status**: Ready for Development  
+**Estimated Completion**: 5-7 days