Phase 2: Design Overview

Welcome to the Design phase of GISE methodology! This is where your carefully gathered requirements transform into concrete architectural blueprints. The Design phase bridges the gap between understanding what you need to build and actually building it.

Phase Objectives

By the end of the Design phase, you will have:

✅ System Architecture Documentation - Complete architectural overview with diagrams and rationale
✅ Database Schema Design - Normalized database structure with relationships and constraints
✅ API Specifications - OpenAPI documentation defining all endpoints and data contracts
✅ Security Architecture - Authentication, authorization, and data protection design
✅ Technical Decision Records - Documented choices with rationale for all major technology decisions

Why Design Matters

The Design Investment Returns:

• 20 hours of quality design saves 100+ hours of refactoring later
• Well-designed systems are 5x easier to maintain and extend
• Clear architecture reduces 90% of integration conflicts during development

The Design Process

The Design phase follows a structured approach that ensures scalable, maintainable architecture:

1. System Architecture (Day 1-3)

Design the overall system structure

• Define system boundaries and responsibilities
• Choose architectural patterns (monolith, microservices, etc.)
• Plan data flow and communication patterns
• Document technology stack decisions with rationale

2. Database Design (Day 4-6)

Create robust data foundation

• Design normalized database schema
• Define relationships, constraints, and indexes
• Plan for scalability and performance
• Document data governance and migration strategies

3. API Specification (Day 7-9)

Define service contracts

• Create OpenAPI specifications for all endpoints
• Design consistent request/response patterns
• Plan versioning and backwards compatibility
• Document authentication and error handling

4. Security Architecture (Day 10-12)

Implement security by design

• Design authentication and authorization flows
• Plan data protection and privacy measures
• Define security boundaries and trust zones
• Create threat model and mitigation strategies

5. Integration Planning (Day 13-15)

Plan system interactions

• Design external service integrations
• Plan event flows and message patterns
• Define monitoring and observability requirements
• Create deployment and operational architecture

6. Technical Review & Validation (Day 16-18)

Ensure design quality and stakeholder buy-in

• Conduct architecture reviews with technical team
• Validate design against requirements
• Get stakeholder approval on technical decisions
• Prepare detailed handoff to development team

Key Deliverables

System Architecture Document

The master blueprint for your system

# System Architecture Document

## Executive Summary
- **Architecture Overview**: [High-level system design and rationale]
- **Technology Decisions**: [Core technology choices with justification]
- **Scalability Plan**: [How the system will grow and evolve]

## System Context
- **Business Requirements**: [Key requirements driving architecture]
- **Quality Attributes**: [Performance, security, maintainability goals]
- **Constraints**: [Technical, regulatory, and business constraints]

## Architecture Views

### Logical Architecture
```mermaid
graph TB
    subgraph "Presentation Layer"
        UI[User Interface]
        API_GW[API Gateway]
    end
    
    subgraph "Application Layer"
        AUTH[Authentication Service]
        BIZ[Business Logic Services]
        WORKFLOW[Workflow Engine]
    end
    
    subgraph "Data Layer"
        DB[(Primary Database)]
        CACHE[(Cache Layer)]
        FILES[(File Storage)]
    end
    
    UI --> API_GW
    API_GW --> AUTH
    API_GW --> BIZ
    BIZ --> WORKFLOW
    AUTH --> DB
    BIZ --> DB
    BIZ --> CACHE
    WORKFLOW --> FILES

Physical Architecture

• Deployment Model: [How components are distributed]
• Infrastructure Requirements: [Servers, containers, networking]
• Scalability Strategy: [Horizontal/vertical scaling approach]

Security Architecture

• Authentication Flow: [How users are verified]
• Authorization Model: [Permission and role management]
• Data Protection: [Encryption, privacy, compliance]

### Database Schema Design
**Normalized data structure with clear relationships**

```sql
-- User Management
CREATE TABLE users (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    email VARCHAR(255) UNIQUE NOT NULL,
    password_hash VARCHAR(255) NOT NULL,
    created_at TIMESTAMP DEFAULT NOW(),
    updated_at TIMESTAMP DEFAULT NOW()
);

-- Business Entities
CREATE TABLE projects (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name VARCHAR(255) NOT NULL,
    description TEXT,
    owner_id UUID REFERENCES users(id),
    created_at TIMESTAMP DEFAULT NOW(),
    updated_at TIMESTAMP DEFAULT NOW()
);

-- Relationships and Constraints
CREATE INDEX idx_projects_owner ON projects(owner_id);
CREATE INDEX idx_users_email ON users(email);

Database Design Rationale:

• UUID Primary Keys: Better for distributed systems and data privacy
• Timestamp Tracking: Audit trail for all changes
• Foreign Key Constraints: Data integrity enforcement
• Appropriate Indexing: Query performance optimization

OpenAPI Specification

Complete API contract documentation

openapi: 3.0.3
info:
  title: Project Management API
  description: RESTful API for project management system
  version: 1.0.0
  
paths:
  /api/v1/projects:
    get:
      summary: List user's projects
      security:
        - BearerAuth: []
      responses:
        '200':
          description: Successfully retrieved projects
          content:
            application/json:
              schema:
                type: object
                properties:
                  data:
                    type: array
                    items:
                      $ref: '#/components/schemas/Project'
                  meta:
                    $ref: '#/components/schemas/PaginationMeta'
    
    post:
      summary: Create new project
      security:
        - BearerAuth: []
      requestBody:
        required: true
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateProjectRequest'
      responses:
        '201':
          description: Project created successfully
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Project'

components:
  schemas:
    Project:
      type: object
      properties:
        id:
          type: string
          format: uuid
        name:
          type: string
          maxLength: 255
        description:
          type: string
        owner_id:
          type: string
          format: uuid
        created_at:
          type: string
          format: date-time
        updated_at:
          type: string
          format: date-time
      required: [id, name, owner_id, created_at, updated_at]
    
  securitySchemes:
    BearerAuth:
      type: http
      scheme: bearer
      bearerFormat: JWT

Technical Decision Records

Documented choices with rationale

# ADR-001: Database Technology Choice

## Status: Accepted

## Context
We need to choose a database technology that supports:
- Strong consistency for financial data
- Complex relationships between entities
- Horizontal scaling for growth
- Strong ecosystem and tooling

## Decision
We will use PostgreSQL as our primary database.

## Rationale
| Criteria | Weight | PostgreSQL | MongoDB | MySQL |
|----------|--------|------------|---------|-------|
| ACID Compliance | 5 | 5 | 2 | 4 |
| Scaling Options | 4 | 4 | 5 | 3 |
| Team Expertise | 4 | 5 | 2 | 4 |
| Ecosystem | 3 | 5 | 4 | 4 |
| **Total Score** | | **4.6** | 3.1 | 3.7 |

## Consequences
- **Positive**: Strong consistency, excellent JSON support, mature ecosystem
- **Negative**: More complex horizontal scaling than NoSQL options
- **Mitigation**: Use read replicas and connection pooling for scalability

GenAI Integration in Design

AI-Assisted Architecture Planning

System Design Prompts:

You are an expert system architect. Based on these requirements:
[INSERT REQUIREMENTS FROM DISCOVER PHASE]

Generate a system architecture that includes:
1. High-level component diagram
2. Data flow between components
3. Technology recommendations with rationale
4. Scalability considerations
5. Security architecture overview

Focus on maintainable, scalable solutions using proven patterns.

Database Schema Generation:

Create a normalized database schema for this system:
[INSERT BUSINESS REQUIREMENTS]

Requirements:
- Use PostgreSQL-compatible SQL
- Include primary keys, foreign keys, and indexes
- Add appropriate constraints and validations
- Include audit fields (created_at, updated_at)
- Provide rationale for design decisions

Generate both the DDL and a visual representation using Mermaid ERD.

Recommended AI Tools for Design

Tool	Best For	Example Usage
ChatGPT/Claude	Architecture planning, design reviews	Generate system diagrams and evaluate trade-offs
GitHub Copilot	API specification writing	Auto-complete OpenAPI schemas
Cursor	Documentation creation	Generate technical decision records
Mermaid Live Editor	Architecture diagrams	Create and iterate on system diagrams

Common Design Challenges

Challenge 1: Over-Engineering

Problem: Creating overly complex architecture for simple requirements

Solutions:

• Start with the simplest solution that meets requirements
• Plan for growth but don't build for it immediately
• Use the "Rule of Three" - refactor when you need the third instance
• Document why simple choices were made

Challenge 2: Technology Selection Paralysis

Problem: Too many technology options, unable to decide

Solutions:

• Create a weighted decision matrix for evaluation
• Consider team expertise and learning curve
• Choose boring, proven technologies over cutting-edge
• Set a decision deadline and stick to it

Challenge 3: Inconsistent API Design

Problem: APIs that don't follow consistent patterns

Solutions:

• Establish API design guidelines early
• Use OpenAPI specifications for all endpoints
• Review API designs before implementation
• Create reusable response patterns and error codes

Challenge 4: Security as an Afterthought

Problem: Security considerations added late in the process

Solutions:

• Include security architecture from the beginning
• Create threat models during design phase
• Plan authentication and authorization flows
• Consider data privacy requirements (GDPR, etc.)

Design Success Patterns

What Great Design Looks Like

Clear Architecture:

• System boundaries are well-defined
• Component responsibilities are clear
• Integration patterns are consistent
• Scalability plan is documented

Robust Data Design:

• Database schema is normalized and efficient
• Relationships are properly modeled
• Indexes support expected query patterns
• Migration strategy is planned

Comprehensive API Design:

• All endpoints are documented with OpenAPI
• Request/response patterns are consistent
• Error handling is standardized
• Versioning strategy is defined

Security by Design:

• Authentication and authorization flows are clear
• Data protection measures are planned
• Security boundaries are defined
• Compliance requirements are addressed

Design Quality Metrics

Track these metrics to ensure design quality:

• Architecture Completeness: 95%+ of system components documented
• API Coverage: 100% of endpoints have OpenAPI specifications
• Security Review: All security requirements addressed
• Stakeholder Approval: 90%+ satisfaction with design decisions

Moving to Development Phase

Handoff Checklist

Before moving to the Development phase, ensure you have:

Architecture Documentation:

• System architecture diagram with component responsibilities
• Technology decisions documented with rationale
• Scalability and performance considerations addressed
• Integration points clearly defined

Data Design:

• Database schema designed and normalized
• Relationships and constraints defined
• Indexes planned for expected queries
• Migration strategy documented

API Specifications:

• OpenAPI specifications for all endpoints
• Request/response schemas defined
• Authentication and error handling documented
• API versioning strategy established

Security Architecture:

• Authentication and authorization flows designed
• Data protection measures planned
• Security boundaries identified
• Compliance requirements addressed

Quality Validation:

• Architecture review completed with technical team
• Design decisions validated against requirements
• Stakeholder approval obtained
• Development team understands the design

Development Phase Preparation

What the Development team needs from Design:

1. Clear Architecture - Component boundaries and interactions
2. Database Schema - Complete data model with relationships
3. API Contracts - OpenAPI specs for all endpoints
4. Security Requirements - Authentication and authorization patterns
5. Technical Decisions - Technology choices with rationale

---

Next Steps

Ready to Start Design?

Follow this sequence to master the Design phase:

1. Architecture Planning - Learn system design techniques
2. Diagram Creation - Master Mermaid architecture diagrams
3. Technical Blueprints - Create comprehensive design documents
4. Pull Request Reviews - Quality gates for design artifacts

Need Quick Reference?

Use the Design Phase Recipes for ready-to-use patterns and templates.

---

Remember: Good design is an investment that pays dividends throughout the entire development lifecycle. Spend the time to get the foundation right.