# Product Requirements Document: Todo Task Management Application

## 1. Overview

The Todo Task Management Application is a comprehensive task organization system that enables users to create, manage, and track their personal and collaborative tasks. The application provides a centralized platform for individuals and teams to organize their work, set priorities, track progress, and ensure timely completion of tasks. This system supports task categorization, deadline management, collaboration features, and progress tracking to enhance productivity and accountability.

---

## 2. User Roles

### 2.1 Guest User
- View public landing page
- Register for a new account
- Log in to existing account

### 2.2 Registered User (Standard)
- Create, read, update, and delete their own tasks
- Organize tasks into lists/categories
- Set task priorities, due dates, and reminders
- Mark tasks as complete/incomplete
- Add notes and descriptions to tasks
- Search and filter their own tasks
- Manage their profile and preferences
- Share tasks with other users
- View tasks shared with them
- Add comments to tasks
- Attach files to tasks

### 2.3 Team Member
- All Standard User capabilities
- View team-shared tasks
- Collaborate on team tasks
- Assign tasks to team members
- View team activity and progress
- Participate in team workspaces

### 2.4 Team Admin
- All Team Member capabilities
- Create and manage teams
- Invite and remove team members
- Assign roles within the team
- Manage team workspaces
- View team analytics and reports
- Configure team settings and permissions

### 2.5 System Administrator
- All Team Admin capabilities across all teams
- Manage all users and accounts
- View system-wide analytics
- Configure system settings
- Manage data retention and backups
- Monitor system health and performance
- Handle user support escalations

---

## 3. Core Entities

### 3.1 User
Represents an individual user account in the system with authentication credentials, profile information, and preferences.

### 3.2 Task
The primary entity representing a todo item with title, description, status, priority, due date, and completion tracking.

### 3.3 List/Category
A container for organizing related tasks into logical groups (e.g., "Work", "Personal", "Shopping").

### 3.4 Tag
A flexible labeling mechanism for categorizing and filtering tasks across different dimensions.

### 3.5 Comment
User-generated notes or discussions attached to specific tasks for collaboration and context.

### 3.6 Attachment
Files or documents associated with tasks (images, PDFs, documents, etc.).

### 3.7 Team
A group of users who collaborate on shared tasks and workspaces.

### 3.8 Workspace
A collaborative environment where teams organize and manage related tasks and projects.

### 3.9 Assignment
The relationship between a task and the user(s) responsible for completing it.

### 3.10 Reminder
Scheduled notifications to alert users about upcoming or overdue tasks.

### 3.11 Activity Log
Audit trail capturing all actions performed on tasks (creation, updates, completion, etc.).

### 3.12 Notification
System-generated alerts for task updates, assignments, mentions, and deadlines.

### 3.13 Subtask
A smaller, component task that is part of a larger parent task.

### 3.14 Recurring Task Template
Configuration for tasks that repeat on a schedule (daily, weekly, monthly, etc.).

---

## 4. Entity Relationships

### 4.1 User Relationships
- **User → Task**: One-to-Many (a user creates many tasks)
- **User → List**: One-to-Many (a user owns many lists)
- **User → Comment**: One-to-Many (a user creates many comments)
- **User → Team**: Many-to-Many (users belong to multiple teams, teams have multiple users)
- **User → Notification**: One-to-Many (a user receives many notifications)
- **User → Activity Log**: One-to-Many (a user generates many activity entries)

### 4.2 Task Relationships
- **Task → User (Creator)**: Many-to-One (many tasks created by one user)
- **Task → User (Assignee)**: Many-to-Many via Assignment (tasks can have multiple assignees)
- **Task → List**: Many-to-One (many tasks belong to one list)
- **Task → Tag**: Many-to-Many (tasks can have multiple tags, tags apply to multiple tasks)
- **Task → Comment**: One-to-Many (a task has many comments)
- **Task → Attachment**: One-to-Many (a task has many attachments)
- **Task → Subtask**: One-to-Many (a task has many subtasks, subtask is a task)
- **Task → Reminder**: One-to-Many (a task can have multiple reminders)
- **Task → Activity Log**: One-to-Many (a task has many activity entries)
- **Task → Workspace**: Many-to-One (many tasks belong to one workspace)
- **Task → Recurring Task Template**: Many-to-One (optional, for recurring tasks)

### 4.3 Team & Workspace Relationships
- **Team → Workspace**: One-to-Many (a team owns many workspaces)
- **Team → User**: Many-to-Many (teams have multiple members)
- **Workspace → Task**: One-to-Many (a workspace contains many tasks)
- **Workspace → List**: One-to-Many (a workspace contains many lists)

### 4.4 Other Relationships
- **List → Task**: One-to-Many (a list contains many tasks)
- **Comment → User**: Many-to-One (many comments by one user)
- **Comment → Task**: Many-to-One (many comments on one task)
- **Attachment → Task**: Many-to-One (many attachments on one task)
- **Notification → User**: Many-to-One (many notifications for one user)

---

## 5. Key Workflows

### 5.1 User Registration & Onboarding
1. Guest visits application landing page
2. Guest clicks "Sign Up" button
3. System displays registration form
4. Guest enters email, password, and basic profile information
5. System validates input and checks for duplicate email
6. System creates new user account
7. System sends verification email
8. User clicks verification link in email
9. System activates account
10. User is redirected to onboarding tutorial
11. User creates their first list and task
12. User is directed to main dashboard

### 5.2 Task Creation & Management
1. User navigates to desired list or workspace
2. User clicks "New Task" button
3. System displays task creation form
4. User enters task title (required)
5. User optionally adds description, due date, priority, tags
6. User optionally assigns task to team members
7. User saves task
8. System validates input
9. System creates task and logs activity
10. System sends notifications to assignees
11. Task appears in relevant views (list, calendar, assignee dashboard)

### 5.3 Task Completion Workflow
1. User views task in their task list
2. User clicks checkbox or "Mark Complete" button
3. System updates task status to "Completed"
4. System records completion timestamp and user
5. System logs activity
6. System sends notifications to relevant users (creator, collaborators)
7. If task is recurring, system creates next instance based on template
8. Task moves to completed section or is hidden based on user preferences
9. System updates progress metrics and analytics

### 5.4 Team Collaboration Workflow
1. Team Admin creates a new team
2. Team Admin invites members via email
3. Invited users receive invitation notification
4. Users accept invitation and join team
5. Team Admin creates workspace for project
6. Team members create and assign tasks within workspace
7. Assigned users receive notifications
8. Team members add comments and attachments to tasks
9. System logs all collaborative activities
10. Team members update task status as work progresses
11. Team Admin monitors progress via team dashboard

### 5.5 Task Assignment & Reassignment
1. Task creator or team admin opens task details
2. User clicks "Assign" button
3. System displays list of eligible assignees (team members or collaborators)
4. User selects one or more assignees
5. User optionally adds assignment note
6. User confirms assignment
7. System creates assignment records
8. System sends notification to new assignees
9. System logs assignment activity
10. Task appears in assignees' task lists
11. If reassigning, system notifies previous assignee of change

### 5.6 Reminder & Notification Workflow
1. User creates or edits a task
2. User sets due date and/or custom reminder times
3. System stores reminder configuration
4. Background scheduler monitors upcoming reminders
5. When reminder time is reached, system generates notification
6. System delivers notification via configured channels (in-app, email, push)
7. User receives and views notification
8. User clicks notification to view task details
9. User takes action on task (complete, snooze, reschedule)
10. System updates task and logs activity

### 5.7 Search & Filter Workflow
1. User navigates to tasks view
2. User enters search query in search bar OR applies filters
3. System processes search/filter criteria:
   - Text search across title, description, comments
   - Filter by status, priority, due date, assignee, tags, list
4. System queries database with criteria
5. System returns matching tasks
6. User views filtered results
7. User can save filter as custom view
8. User can clear filters to return to default view

---

## 6. Features & Requirements

### 6.1 Authentication & User Management

#### 6.1.1 User Registration
- **REQ-AUTH-001**: System shall allow users to register with email and password
- **REQ-AUTH-002**: System shall validate email format and password strength (min 8 characters, 1 uppercase, 1 number)
- **REQ-AUTH-003**: System shall send verification email upon registration
- **REQ-AUTH-004**: System shall prevent duplicate email registrations
- **REQ-AUTH-005**: System shall support OAuth authentication (Google, Microsoft)

#### 6.1.2 User Login
- **REQ-AUTH-006**: System shall authenticate users with email/password
- **REQ-AUTH-007**: System shall implement session management with secure tokens
- **REQ-AUTH-008**: System shall provide "Remember Me" functionality
- **REQ-AUTH-009**: System shall lock account after 5 failed login attempts
- **REQ-AUTH-010**: System shall provide password reset via email

#### 6.1.3 Profile Management
- **REQ-USER-001**: Users shall be able to update profile information (name, avatar, bio)
- **REQ-USER-002**: Users shall be able to change password
- **REQ-USER-003**: Users shall be able to configure notification preferences
- **REQ-USER-004**: Users shall be able to set timezone and date format preferences
- **REQ-USER-005**: Users shall be able to delete their account

### 6.2 Task Management

#### 6.2.1 Task CRUD Operations
- **REQ-TASK-001**: Users shall be able to create tasks with title (required)
- **REQ-TASK-002**: Users shall be able to add description (rich text) to tasks
- **REQ-TASK-003**: Users shall be able to set due date and time for tasks
- **REQ-TASK-004**: Users shall be able to set priority (Low, Medium, High, Urgent)
- **REQ-TASK-005**: Users shall be able to edit all task properties
- **REQ-TASK-006**: Users shall be able to delete tasks they own
- **REQ-TASK-007**: System shall soft-delete tasks and allow recovery within 30 days
- **REQ-TASK-008**: Users shall be able to duplicate tasks

#### 6.2.2 Task Status Management
- **REQ-TASK-009**: Tasks shall have status: Not Started, In Progress, Completed, Archived
- **REQ-TASK-010**: Users shall be able to mark tasks as complete/incomplete
- **REQ-TASK-011**: System shall record completion timestamp and user
- **REQ-TASK-012**: Users shall be able to archive completed tasks
- **REQ-TASK-013**: System shall display task progress percentage for tasks with subtasks

#### 6.2.3 Subtasks
- **REQ-TASK-014**: Users shall be able to add subtasks to any task
- **REQ-TASK-015**: Subtasks shall support all properties of parent tasks
- **REQ-TASK-016**: System shall calculate parent task progress based on subtask completion
- **REQ-TASK-017**: Subtasks shall be limited to 2 levels of nesting
- **REQ-TASK-018**: Completing all subtasks shall prompt user to complete parent task

#### 6.2.4 Task Views
- **REQ-TASK-019**: System shall provide List view (default)
- **REQ-TASK-020**: System shall provide Board/Kanban view
- **REQ-TASK-021**: System shall provide Calendar view
- **REQ-TASK-022**: System shall provide Timeline/Gantt view
- **REQ-TASK-023**: Users shall be able to switch between views seamlessly

### 6.3 Lists & Organization

#### 6.3.1 List Management
- **REQ-LIST-001**: Users shall be able to create custom lists
- **REQ-LIST-002**: Users shall be able to rename and delete lists
- **REQ-LIST-003**: System shall provide default lists (Inbox, Today, Upcoming)
- **REQ-LIST-004**: Users shall be able to reorder lists via drag-and-drop
- **REQ-LIST-005**: Users shall be able to set list color and icon
- **REQ-LIST-006**: Users shall be able to share lists with other users
- **REQ-LIST-007**: System shall prevent deletion of lists containing tasks (require move or delete tasks first)

#### 6.3.2 Tags
- **REQ-TAG-001**: Users shall be able to create custom tags
- **REQ-TAG-002**: Users shall be able to apply multiple tags to tasks
- **REQ-TAG-003**: System shall suggest existing tags during task creation
- **REQ-TAG-004**: Users shall be able to filter tasks by tags
- **REQ-TAG-005**: Users shall be able to set tag colors
- **REQ-TAG-006**: System shall display tag usage count

### 6.4 Collaboration Features

#### 6.4.1 Task Sharing
- **REQ-COLLAB-001**: Users shall be able to share individual tasks with other users
- **REQ-COLLAB-002**: Task owner shall be able to set permissions (view, edit, comment)
- **REQ-COLLAB-003**: Shared users shall receive notification of shared task
- **REQ-COLLAB-004**: Users shall be able to unshare tasks
- **REQ-COLLAB-005**: System shall display all collaborators on task detail view

#### 6.4.2 Comments
- **REQ-COLLAB-006**: Users shall be able to add comments to tasks
- **REQ-COLLAB-007**: Comments shall support text formatting and mentions (@username)
- **REQ-COLLAB-008**: Users shall be able to edit and delete their own comments
- **REQ-COLLAB-009**: System shall notify mentioned users
- **REQ-COLLAB-010**: Comments shall display timestamp and author
- **REQ-COLLAB-011**: System shall support comment threading/replies

#### 6.4.3 Attachments
- **REQ-COLLAB-012**: Users shall be able to attach files to tasks
- **REQ-COLLAB-013**: System shall support common file types (PDF, DOC, XLS, images, etc.)
- **REQ-COLLAB-014**: System shall limit individual file size to 10MB
- **REQ-COLLAB-015**: System shall limit total attachments per task to 50MB
- **REQ-COLLAB-016**: Users shall be able to preview images inline
- **REQ-COLLAB-017**: Users shall be able to download attachments
- **REQ-COLLAB-018**: Users shall be able to delete attachments they uploaded

#### 6.4.4 Task Assignment
- **REQ-COLLAB-019**: Users shall be able to assign tasks to team members
- **REQ-COLLAB-020**: Tasks shall support multiple assignees
- **REQ-COLLAB-021**: Assignees shall receive notification of assignment
- **REQ-COLLAB-022**: Users shall be able to reassign tasks
- **REQ-COLLAB-023**: System shall track assignment history

### 6.5 Team & Workspace Management

#### 6.5.1 Team Management
- **REQ-TEAM-001**: Users shall be able to create teams
- **REQ-TEAM-002**: Team creators shall automatically become Team Admin
- **REQ-TEAM-003**: Team Admins shall be able to invite members via email
- **REQ-TEAM-004**: Team Admins shall be able to remove members
- **REQ-TEAM-005**: Team Admins shall be able to assign roles (Member, Admin)
- **REQ-TEAM-006**: Users shall be able to leave teams (except last admin)
- **REQ-TEAM-007**: System shall support team size up to 50 members

#### 6.5.2 Workspace Management
- **REQ-WORKSPACE-001**: Team Admins shall be able to create workspaces
- **REQ-WORKSPACE-002**: Workspaces shall contain lists and tasks
- **REQ-WORKSPACE-003**: All team members shall have access to team workspaces
- **REQ-WORKSPACE-004**: Workspace creators shall be able to set workspace permissions
- **REQ-WORKSPACE-005**: Users shall be able to switch between personal and team workspaces
- **REQ-WORKSPACE-006**: System shall display workspace activity feed

### 6.6 Reminders & Notifications

#### 6.6.1 Reminders
- **REQ-REMIND-001**: Users shall be able to set custom reminder times for tasks
- **REQ-REMIND-002**: System shall support multiple reminders per task
- **REQ-REMIND-003**: System shall provide preset reminder options (1 hour before, 1 day before, etc.)
- **REQ-REMIND-004**: System shall send reminders via in-app notification and email
- **REQ-REMIND-005**: Users shall be able to snooze reminders
- **REQ-REMIND-006**: System shall automatically remind users of overdue tasks daily

#### 6.6.2 Notifications
- **REQ-NOTIF-001**: System shall notify users of task assignments
- **REQ-NOTIF-002**: System shall notify users when mentioned in comments
- **REQ-NOTIF-003**: System shall notify users of task updates on shared tasks
- **REQ-NOTIF-004**: System shall notify users of approaching due dates
- **REQ-NOTIF-005**: Users shall be able to configure notification preferences per type
- **REQ-NOTIF-006**: System shall provide in-app notification center
- **REQ-NOTIF-007**: Users shall be able to mark notifications as read
- **REQ-NOTIF-008**: System shall support email notification digest (daily/weekly)

### 6.7 Recurring Tasks

- **REQ-RECUR-001**: Users shall be able to set tasks as recurring
- **REQ-RECUR-002**: System shall support recurrence patterns: daily, weekly, monthly, yearly, custom
- **REQ-RECUR-003**: Users shall be able to specify recurrence end date or number of occurrences
- **REQ-RECUR-004**: System shall automatically create next instance when current is completed
- **REQ-RECUR-005**: Users shall be able to edit single instance or entire series
- **REQ-RECUR-006**: Users shall be able to skip recurring task instances
- **REQ-RECUR-007**: System shall maintain link between recurring task instances

### 6.8 Search & Filtering

#### 6.8.1 Search
- **REQ-SEARCH-001**: System shall provide global search across all tasks
- **REQ-SEARCH-002**: Search shall index task title, description, and comments
- **REQ-SEARCH-003**: System shall support partial text matching
- **REQ-SEARCH-004**: System shall highlight search terms in results
- **REQ-SEARCH-005**: Search shall return results in real-time (as user types)

#### 6.8.2 Filtering & Sorting
- **REQ-FILTER-001**: Users shall be able to filter tasks by status
- **REQ-FILTER-002**: Users shall be able to filter tasks by priority
- **REQ-FILTER-003**: Users shall be able to filter tasks by due date range
- **REQ-FILTER-004**: Users shall be able to filter tasks by assignee
- **REQ-FILTER-005**: Users shall be able to filter tasks by tags
- **REQ-FILTER-006**: Users shall be able to filter tasks by list/workspace
- **REQ-FILTER-007**: Users shall be able to combine multiple filters
- **REQ-FILTER-008**: Users shall be able to sort tasks by due date, priority, creation date, title
- **REQ-FILTER-009**: Users shall be able to save custom filter combinations as views

### 6.9 Analytics & Reporting

- **REQ-ANALYTICS-001**: System shall display task completion statistics
- **REQ-ANALYTICS-002**: System shall show productivity trends over time
- **REQ-ANALYTICS-003**: Users shall be able to view personal productivity dashboard
- **REQ-ANALYTICS-004**: Team Admins shall be able to view team performance metrics
- **REQ-ANALYTICS-005**: System shall display overdue task count
- **REQ-ANALYTICS-006**: System shall show task completion rate by list/workspace
- **REQ-ANALYTICS-007**: System shall provide exportable reports (CSV, PDF)
- **REQ-ANALYTICS-008**: System shall track time-to-completion metrics

### 6.10 Mobile & Responsive Design

- **REQ-MOBILE-001**: Application shall be fully responsive across desktop, tablet, mobile
- **REQ-MOBILE-002**: Mobile interface shall support touch gestures (swipe to complete, etc.)
- **REQ-MOBILE-003**: Application shall support offline mode with sync when online
- **REQ-MOBILE-004**: Mobile interface shall provide quick-add task functionality
- **REQ-MOBILE-005**: Application shall support push notifications on mobile devices

---

## 7. Business Rules

### 7.1 Task Rules
- **BR-TASK-001**: Task title is mandatory and must be between 1-500 characters
- **BR-TASK-002**: Task description is optional and limited to 10,000 characters
- **BR-TASK-003**: Due date, if set, cannot be in the past (except when editing existing tasks)
- **BR-TASK-004**: Completed tasks cannot be edited unless marked as incomplete first
- **BR-TASK-005**: Deleted tasks are soft-deleted and retained for 30 days before permanent deletion
- **BR-TASK-006**: Tasks must belong to exactly one list
- **BR-TASK-007**: Subtasks inherit workspace/team context from parent task
- **BR-TASK-008**: Maximum subtask nesting depth is 2 levels
- **BR-TASK-009**: A task cannot be its own subtask (prevent circular references)

### 7.2 User & Permission Rules
- **BR-USER-001**: Email addresses must be unique across the system
- **BR-USER-002**: Users can only delete tasks they created or have admin rights to
- **BR-USER-003**: Users can only view tasks they created, are assigned to, or have been shared with
- **BR-USER-004**: Task creator always retains full permissions regardless of sharing settings
- **BR-USER-005**: Users must verify email before accessing full application features
- **BR-USER-006**: Inactive accounts (no login for 365 days) are flagged for review

### 7.3 Team & Workspace Rules
- **BR-TEAM-001**: Team name must be unique within the system
- **BR-TEAM-002**: Teams must have at least one admin at all times
- **BR-TEAM-003**: Maximum team size is 50 members
- **BR-TEAM-004**: Users cannot be invited to a team they're already a member of
- **BR-TEAM-005**: Workspace names must be unique within a team
- **BR-TEAM-006**: Deleting a team requires confirmation and moves all tasks to members' personal workspaces
- **BR-TEAM-007**: Only team members can be assigned to tasks in team workspaces

### 7.4 Collaboration Rules
- **BR-COLLAB-001**: Users can only share tasks with registered users
- **BR-COLLAB-002**: Comments cannot be empty and are limited to 2,000 characters
- **BR-COLLAB-003**: Users can only edit/delete their own comments
- **BR-COLLAB-004**: Attachments must not exceed 10MB per file
- **BR-COLLAB-005**: Total attachments per task cannot exceed 50MB
- **BR-COLLAB-006**: Supported file types: PDF, DOC, DOCX, XLS, XLSX, PPT, PPTX, TXT, JPG, PNG, GIF
- **BR-COLLAB-007**: Mentions in comments must reference valid, active users

### 7.5 Notification Rules
- **BR-NOTIF-001**: Users receive notifications only for events they're involved in
- **BR-NOTIF-002**: Notification preferences override default notification behavior
- **BR-NOTIF-003**: Email notifications are throttled to prevent spam (max 50 per hour per user)
- **BR-NOTIF-004**: Reminder notifications are sent at exact scheduled time (±2 minutes)
- **BR-NOTIF-005**: Overdue task reminders are sent once daily at 9 AM user local time

### 7.6 Recurring Task Rules
- **BR-RECUR-001**: Recurring tasks must have a valid recurrence pattern
- **BR-RECUR-002**: Next instance is created only after current instance is marked complete
- **BR-RECUR-003**: Editing a recurring task series updates all future instances, not past ones
- **BR-RECUR-004**: Deleting a recurring task series requires explicit confirmation
- **BR-RECUR-005**: Recurring tasks without end date are limited to 100 future instances

### 7.7 Data Retention Rules
- **BR-DATA-001**: Soft-deleted tasks are permanently deleted after 30 days
- **BR-DATA-002**: Activity logs are retained for 90 days
- **BR-DATA-003**: Completed tasks are retained indefinitely unless explicitly deleted
- **BR-DATA-004**: User accounts marked for deletion are purged after 30-day grace period
- **BR-DATA-005**: Attachments are deleted when parent task is permanently deleted

### 7.8 Search & Filter Rules
- **BR-SEARCH-001**: Search queries are limited to 200 characters
- **BR-SEARCH-002**: Search results are limited to 100 items per page
- **BR-SEARCH-003**: Filters respect user permissions (only show accessible tasks)
- **BR-SEARCH-004**: Saved views are private to the user who created them
- **BR-SEARCH-005**: Maximum of 20 saved views per user

---

## 8. Non-Functional Requirements

### 8.1 Performance

- **NFR-PERF-001**: Page load time shall not exceed 2 seconds on standard broadband connection
- **NFR-PERF-002**: Task creation/update operations shall complete within 500ms
- **NFR-PERF-003**: Search results shall return within 1 second for queries across 10,000 tasks
- **NFR-PERF-004**: System shall support 1,000 concurrent users without degradation
- **NFR-PERF-005**: API response time shall be under 200ms for 95% of requests
- **NFR-PERF-006**: Database queries shall be optimized with appropriate indexing
- **NFR-PERF-007**: Real-time notifications shall be delivered within 5 seconds of event
- **NFR-PERF-008**: File uploads shall support resumable uploads for files >5MB

### 8.2 Security

- **NFR-SEC-001**: All data transmission shall use HTTPS/TLS 1.3 or higher
- **NFR-SEC-002**: Passwords shall be hashed using bcrypt with minimum 10 rounds
- **NFR-SEC-003**: Authentication tokens shall expire after 24 hours of inactivity
- **NFR-SEC-004**: System shall implement CSRF protection on all state-changing operations
- **NFR-SEC-005**: System shall sanitize all user input to prevent XSS attacks
- **NFR-SEC-006**: System shall implement rate limiting (100 requests per minute per user)
- **NFR-SEC-007**: System shall log all authentication attempts and security events
- **NFR-SEC-008**: File uploads shall be scanned for malware before storage
- **NFR-SEC-009**: System shall implement SQL injection prevention via parameterized queries
- **NFR-SEC-010**: Sensitive data (passwords, tokens) shall never be logged
- **NFR-SEC-011**: System shall support two-factor authentication (2FA) as optional feature
- **NFR-SEC-012**: API endpoints shall require authentication except public endpoints

### 8.3 Scalability

- **NFR-SCALE-001**: System architecture shall support horizontal scaling
- **NFR-SCALE-002**: Database shall support read replicas for query distribution
- **NFR-SCALE-003**: System shall handle 100,000 registered users
- **NFR-SCALE-004**: System shall support 1 million tasks across all users
- **NFR-SCALE-005**: File storage shall use cloud object storage (S3-compatible)
- **NFR-SCALE-006**: System shall implement caching for frequently accessed data
- **NFR-SCALE-007**: Background jobs (reminders, notifications) shall use queue system

### 8.4 Reliability & Availability

- **NFR-REL-001**: System shall maintain 99.5% uptime (excluding planned maintenance)
- **NFR-REL-002**: System shall perform automated daily backups
- **NFR-REL-003**: System shall support point-in-time recovery within 24 hours
- **NFR-REL-004**: System shall implement graceful degradation when services are unavailable
- **NFR-REL-005**: System shall have automated health checks and monitoring
- **NFR-REL-006**: Critical errors shall trigger automated alerts to operations team
- **NFR-REL-007**: System shall implement retry logic for transient failures

### 8.5 Usability

- **NFR-USE-001**: Application shall follow WCAG 2.1 Level AA accessibility guidelines
- **NFR-USE-002**: Application shall support keyboard navigation for all features
- **NFR-USE-003**: Application shall provide helpful error messages with recovery suggestions
- **NFR-USE-004**: Application shall support undo for destructive actions
- **NFR-USE-005**: Application shall provide contextual help and tooltips
- **NFR-USE-006**: Application shall support internationalization (i18n) framework
- **NFR-USE-007**: Application shall maintain consistent UI/UX patterns throughout
- **NFR-USE-008**: Application shall provide loading indicators for async operations

### 8.6 Compatibility

- **NFR-COMPAT-001**: Application shall support modern browsers (Chrome, Firefox, Safari, Edge) - latest 2 versions
- **NFR-COMPAT-002**: Application shall support iOS 14+ and Android 10+
- **NFR-COMPAT-003**: Application shall degrade gracefully on older browsers
- **NFR-COMPAT-004**: API shall follow RESTful conventions and versioning
- **NFR-COMPAT-005**: System shall support data export in standard formats (JSON, CSV)

### 8.7 Maintainability

- **NFR-MAINT-001**: Code shall follow established style guides and linting rules
- **NFR-MAINT-002**: System shall have comprehensive API documentation
- **NFR-MAINT-003**: System shall maintain minimum 80% code test coverage
- **NFR-MAINT-004**: System shall use semantic versioning for releases
- **NFR-MAINT-005**: System shall implement structured logging with appropriate log levels
- **NFR-MAINT-006**: Database migrations shall be reversible
- **NFR-MAINT-007**: System shall separate configuration from code (12-factor app principles)

### 8.8 Data Privacy & Compliance

- **NFR-PRIVACY-001**: System shall comply with GDPR requirements
- **NFR-PRIVACY-002**: Users shall be able to export all their data
- **NFR-PRIVACY-003**: Users shall be able to request complete data deletion
- **NFR-PRIVACY-004**: System shall provide privacy policy and terms of service
- **NFR-PRIVACY-005**: System shall obtain explicit consent for data processing
- **NFR-PRIVACY-006**: System shall encrypt sensitive data at rest
- **NFR-PRIVACY-007**: System shall implement data retention policies per business rules

### 8.9 Monitoring & Analytics

- **NFR-MONITOR-001**: System shall track application performance metrics (APM)
- **NFR-MONITOR-002**: System shall monitor error rates and types
- **NFR-MONITOR-003**: System shall track user engagement metrics
- **NFR-MONITOR-004**: System shall implement audit logging for compliance
- **NFR-MONITOR-005**: System shall provide admin dashboard for system health
- **NFR-MONITOR-006**: System shall alert on anomalous behavior patterns

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## Appendix: Future Considerations

The following features are out of scope for the initial release but may be considered for future iterations:

- Calendar integration (Google Calendar, Outlook)
- Time tracking functionality
- Gantt chart advanced project management features
- Custom workflows and automation rules
- Third-party integrations (Slack, Microsoft Teams, etc.)
- AI-powered task suggestions and prioritization
- Voice input for task creation
- Native mobile applications (iOS/Android)
- Advanced reporting and business intelligence
- Custom fields and task templates
- Budget and resource management
- Client portal for external stakeholders

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**Document Version**: 1.0  
**Last Updated**: 2025-01-10  
**Document Owner**: Senior Product Manager  
**Status**: Ready for Development