diff --git a/openspec/changes/migrate-to-external-api-authentication/database_schema.sql b/openspec/changes/migrate-to-external-api-authentication/database_schema.sql
new file mode 100644
index 0000000..13a58e6
--- /dev/null
+++ b/openspec/changes/migrate-to-external-api-authentication/database_schema.sql
@@ -0,0 +1,183 @@
+-- Tool_OCR Database Schema with External API Authentication
+-- Version: 2.0.0
+-- Date: 2025-11-14
+-- Description: Complete database redesign with user task isolation and history
+
+-- ============================================
+-- Drop existing tables (if needed)
+-- ============================================
+-- Uncomment these lines to drop existing tables
+-- DROP TABLE IF EXISTS tool_ocr_sessions;
+-- DROP TABLE IF EXISTS tool_ocr_task_files;
+-- DROP TABLE IF EXISTS tool_ocr_tasks;
+-- DROP TABLE IF EXISTS tool_ocr_users;
+
+-- ============================================
+-- 1. Users Table
+-- ============================================
+CREATE TABLE IF NOT EXISTS tool_ocr_users (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    email VARCHAR(255) UNIQUE NOT NULL COMMENT 'Primary identifier from Azure AD',
+    display_name VARCHAR(255) COMMENT 'Display name from API response',
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    last_login TIMESTAMP NULL,
+    is_active BOOLEAN DEFAULT TRUE,
+    INDEX idx_email (email),
+    INDEX idx_active (is_active)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+COMMENT='User accounts authenticated via external API';
+
+-- ============================================
+-- 2. OCR Tasks Table
+-- ============================================
+CREATE TABLE IF NOT EXISTS tool_ocr_tasks (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    user_id INT NOT NULL COMMENT 'Foreign key to users table',
+    task_id VARCHAR(255) UNIQUE NOT NULL COMMENT 'Unique task identifier (UUID)',
+    filename VARCHAR(255),
+    file_type VARCHAR(50),
+    status ENUM('pending', 'processing', 'completed', 'failed') DEFAULT 'pending',
+    result_json_path VARCHAR(500) COMMENT 'Path to JSON result file',
+    result_markdown_path VARCHAR(500) COMMENT 'Path to Markdown result file',
+    result_pdf_path VARCHAR(500) COMMENT 'Path to searchable PDF file',
+    error_message TEXT COMMENT 'Error details if task failed',
+    processing_time_ms INT COMMENT 'Processing time in milliseconds',
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+    completed_at TIMESTAMP NULL,
+    file_deleted BOOLEAN DEFAULT FALSE COMMENT 'Track if files were auto-deleted',
+    FOREIGN KEY (user_id) REFERENCES tool_ocr_users(id) ON DELETE CASCADE,
+    INDEX idx_user_status (user_id, status),
+    INDEX idx_created (created_at),
+    INDEX idx_task_id (task_id),
+    INDEX idx_filename (filename)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+COMMENT='OCR processing tasks with user association';
+
+-- ============================================
+-- 3. Task Files Table
+-- ============================================
+CREATE TABLE IF NOT EXISTS tool_ocr_task_files (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    task_id INT NOT NULL COMMENT 'Foreign key to tasks table',
+    original_name VARCHAR(255),
+    stored_path VARCHAR(500) COMMENT 'Actual file path on server',
+    file_size BIGINT COMMENT 'File size in bytes',
+    mime_type VARCHAR(100),
+    file_hash VARCHAR(64) COMMENT 'SHA256 hash for deduplication',
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    FOREIGN KEY (task_id) REFERENCES tool_ocr_tasks(id) ON DELETE CASCADE,
+    INDEX idx_task (task_id),
+    INDEX idx_hash (file_hash)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+COMMENT='Files associated with OCR tasks';
+
+-- ============================================
+-- 4. Sessions Table (Token Storage)
+-- ============================================
+CREATE TABLE IF NOT EXISTS tool_ocr_sessions (
+    id INT PRIMARY KEY AUTO_INCREMENT,
+    user_id INT NOT NULL COMMENT 'Foreign key to users table',
+    session_id VARCHAR(255) UNIQUE NOT NULL COMMENT 'Unique session identifier',
+    access_token TEXT COMMENT 'Azure AD access token (encrypted)',
+    id_token TEXT COMMENT 'Azure AD ID token (encrypted)',
+    refresh_token TEXT COMMENT 'Refresh token if available',
+    expires_at TIMESTAMP NOT NULL COMMENT 'Token expiration time',
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    last_accessed TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+    is_active BOOLEAN DEFAULT TRUE,
+    ip_address VARCHAR(45) COMMENT 'Client IP address',
+    user_agent TEXT COMMENT 'Client user agent',
+    FOREIGN KEY (user_id) REFERENCES tool_ocr_users(id) ON DELETE CASCADE,
+    INDEX idx_user (user_id),
+    INDEX idx_session (session_id),
+    INDEX idx_expires (expires_at),
+    INDEX idx_active (is_active)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+COMMENT='User session and token management';
+
+-- ============================================
+-- 5. Audit Log Table (Optional)
+-- ============================================
+CREATE TABLE IF NOT EXISTS tool_ocr_audit_logs (
+    id BIGINT PRIMARY KEY AUTO_INCREMENT,
+    user_id INT COMMENT 'User who performed the action',
+    action VARCHAR(100) NOT NULL COMMENT 'Action performed',
+    entity_type VARCHAR(50) COMMENT 'Type of entity affected',
+    entity_id INT COMMENT 'ID of entity affected',
+    details JSON COMMENT 'Additional details in JSON format',
+    ip_address VARCHAR(45),
+    user_agent TEXT,
+    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+    INDEX idx_user (user_id),
+    INDEX idx_action (action),
+    INDEX idx_created (created_at)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
+COMMENT='Audit trail for all system actions';
+
+-- ============================================
+-- Views for Common Queries
+-- ============================================
+
+-- User task statistics view
+CREATE OR REPLACE VIEW tool_ocr_user_stats AS
+SELECT
+    u.id as user_id,
+    u.email,
+    u.display_name,
+    COUNT(DISTINCT t.id) as total_tasks,
+    SUM(CASE WHEN t.status = 'completed' THEN 1 ELSE 0 END) as completed_tasks,
+    SUM(CASE WHEN t.status = 'failed' THEN 1 ELSE 0 END) as failed_tasks,
+    SUM(CASE WHEN t.status = 'processing' THEN 1 ELSE 0 END) as processing_tasks,
+    SUM(CASE WHEN t.status = 'pending' THEN 1 ELSE 0 END) as pending_tasks,
+    AVG(t.processing_time_ms) as avg_processing_time_ms,
+    MAX(t.created_at) as last_task_created
+FROM tool_ocr_users u
+LEFT JOIN tool_ocr_tasks t ON u.id = t.user_id
+GROUP BY u.id, u.email, u.display_name;
+
+-- Recent tasks view
+CREATE OR REPLACE VIEW tool_ocr_recent_tasks AS
+SELECT
+    t.*,
+    u.email as user_email,
+    u.display_name as user_name
+FROM tool_ocr_tasks t
+INNER JOIN tool_ocr_users u ON t.user_id = u.id
+ORDER BY t.created_at DESC
+LIMIT 100;
+
+-- ============================================
+-- Stored Procedures (Optional)
+-- ============================================
+
+DELIMITER $$
+
+-- Procedure to clean up expired sessions
+CREATE PROCEDURE IF NOT EXISTS cleanup_expired_sessions()
+BEGIN
+    DELETE FROM tool_ocr_sessions
+    WHERE expires_at < NOW() OR is_active = FALSE;
+END$$
+
+-- Procedure to clean up old tasks
+CREATE PROCEDURE IF NOT EXISTS cleanup_old_tasks(IN days_to_keep INT)
+BEGIN
+    UPDATE tool_ocr_tasks
+    SET file_deleted = TRUE
+    WHERE created_at < DATE_SUB(NOW(), INTERVAL days_to_keep DAY)
+    AND status IN ('completed', 'failed');
+END$$
+
+DELIMITER ;
+
+-- ============================================
+-- Initial Data (Optional)
+-- ============================================
+-- Add any initial data here if needed
+
+-- ============================================
+-- Grants (Adjust as needed)
+-- ============================================
+-- GRANT ALL PRIVILEGES ON tool_ocr_* TO 'tool_ocr_user'@'localhost';
+-- FLUSH PRIVILEGES;
\ No newline at end of file
diff --git a/openspec/changes/migrate-to-external-api-authentication/proposal.md b/openspec/changes/migrate-to-external-api-authentication/proposal.md
index 0737d79..21bcccb 100644
--- a/openspec/changes/migrate-to-external-api-authentication/proposal.md
+++ b/openspec/changes/migrate-to-external-api-authentication/proposal.md
@@ -75,9 +75,11 @@ By migrating to the external API authentication service at https://pj-auth-api.v
 
 **Complete Redesign (No backward compatibility needed)**:
 
-1. **users table (redesigned)**:
+**Table Prefix**: `tool_ocr_` (for clear separation from other systems in the same database)
+
+1. **tool_ocr_users table (redesigned)**:
    ```sql
-   CREATE TABLE users (
+   CREATE TABLE tool_ocr_users (
      id INT PRIMARY KEY AUTO_INCREMENT,
      email VARCHAR(255) UNIQUE NOT NULL,  -- Primary identifier from Azure AD
      display_name VARCHAR(255),            -- Display name from API response
@@ -88,9 +90,9 @@ By migrating to the external API authentication service at https://pj-auth-api.v
    ```
    Note: No Azure AD ID storage needed - email is sufficient as unique identifier
 
-2. **ocr_tasks table (new - for task history)**:
+2. **tool_ocr_tasks table (new - for task history)**:
    ```sql
-   CREATE TABLE ocr_tasks (
+   CREATE TABLE tool_ocr_tasks (
      id INT PRIMARY KEY AUTO_INCREMENT,
      user_id INT NOT NULL,                 -- Foreign key to users table
      task_id VARCHAR(255) UNIQUE,          -- Unique task identifier
@@ -104,22 +106,37 @@ By migrating to the external API authentication service at https://pj-auth-api.v
      updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
      completed_at TIMESTAMP NULL,
      file_deleted BOOLEAN DEFAULT FALSE,   -- Track if files were auto-deleted
-     FOREIGN KEY (user_id) REFERENCES users(id),
+     FOREIGN KEY (user_id) REFERENCES tool_ocr_users(id),
      INDEX idx_user_status (user_id, status),
      INDEX idx_created (created_at)
    );
    ```
 
-3. **task_files table (for multiple files per task)**:
+3. **tool_ocr_task_files table (for multiple files per task)**:
    ```sql
-   CREATE TABLE task_files (
+   CREATE TABLE tool_ocr_task_files (
      id INT PRIMARY KEY AUTO_INCREMENT,
      task_id INT NOT NULL,
      original_name VARCHAR(255),
      stored_path VARCHAR(500),
      file_size BIGINT,
      mime_type VARCHAR(100),
-     FOREIGN KEY (task_id) REFERENCES ocr_tasks(id) ON DELETE CASCADE
+     FOREIGN KEY (task_id) REFERENCES tool_ocr_tasks(id) ON DELETE CASCADE
+   );
+   ```
+
+4. **tool_ocr_sessions table (for token management)**:
+   ```sql
+   CREATE TABLE tool_ocr_sessions (
+     id INT PRIMARY KEY AUTO_INCREMENT,
+     user_id INT NOT NULL,
+     access_token TEXT,
+     id_token TEXT,
+     expires_at TIMESTAMP,
+     created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+     FOREIGN KEY (user_id) REFERENCES tool_ocr_users(id) ON DELETE CASCADE,
+     INDEX idx_user (user_id),
+     INDEX idx_expires (expires_at)
    );
    ```
 
@@ -227,6 +244,7 @@ By migrating to the external API authentication service at https://pj-auth-api.v
   - `TASK_RETENTION_DAYS` = 30 (auto-delete old tasks)
   - `MAX_TASKS_PER_USER` = 1000 (limit per user)
   - `ENABLE_TASK_HISTORY` = true (enable history feature)
+  - `DATABASE_TABLE_PREFIX` = "tool_ocr_" (table naming prefix)
 
 ### Security Considerations
 - HTTPS required for all authentication requests
diff --git a/openspec/changes/migrate-to-external-api-authentication/tasks.md b/openspec/changes/migrate-to-external-api-authentication/tasks.md
index c2d18de..40528b6 100644
--- a/openspec/changes/migrate-to-external-api-authentication/tasks.md
+++ b/openspec/changes/migrate-to-external-api-authentication/tasks.md
@@ -5,21 +5,23 @@
   - Export current schema and data
   - Document any important data to preserve
 - [ ] 1.2 Drop old tables
-  - Remove existing users table
-  - Remove any related tables
+  - Remove existing tables with old naming convention
   - Clear database for fresh start
-- [ ] 1.3 Create new database schema
-  - Create new `users` table (email as primary identifier)
-  - Create `ocr_tasks` table with user association
-  - Create `task_files` table for file tracking
+- [ ] 1.3 Create new database schema with `tool_ocr_` prefix
+  - Create new `tool_ocr_users` table (email as primary identifier)
+  - Create `tool_ocr_tasks` table with user association
+  - Create `tool_ocr_task_files` table for file tracking
+  - Create `tool_ocr_sessions` table for token storage
   - Add proper indexes for performance
 - [ ] 1.4 Create SQLAlchemy models
-  - User model (simplified)
-  - Task model with user relationship
-  - TaskFile model with cascade delete
+  - User model (mapped to `tool_ocr_users`)
+  - Task model (mapped to `tool_ocr_tasks`)
+  - TaskFile model (mapped to `tool_ocr_task_files`)
+  - Session model (mapped to `tool_ocr_sessions`)
+  - Configure table prefix in base model
 - [ ] 1.5 Generate Alembic migration
   - Create initial migration for new schema
-  - Test migration script
+  - Test migration script with proper table prefixes
 
 ## 2. Configuration Management
 - [ ] 2.1 Update environment configuration
@@ -30,9 +32,11 @@
   - Add `TASK_RETENTION_DAYS` for auto-cleanup
   - Add `MAX_TASKS_PER_USER` for limits
   - Add `ENABLE_TASK_HISTORY` feature flag
+  - Add `DATABASE_TABLE_PREFIX` = "tool_ocr_"
 - [ ] 2.2 Update Settings class
   - Add external auth settings to `backend/app/core/config.py`
   - Add task management settings
+  - Add database table prefix configuration
   - Add validation for new configuration values
   - Remove old authentication settings