Updating Stage 07 on modernizr workflow

workshops/modernizr/entity_relationships_diagram.md

@@ -0,0 +1,118 @@
+# Entity Relationship Diagram - Modernizr E-commerce Platform
+
+This diagram shows the entity relationships for the DynamoDB design based on the API access patterns analysis.
+
+```mermaid
+erDiagram
+    USERS {
+        string id PK
+        string username UK "Unique"
+        string email UK "Unique"
+        string password_hash
+        string first_name
+        string last_name
+        boolean is_seller
+        datetime created_at
+        datetime updated_at
+    }
+
+    CATEGORIES {
+        string id PK
+        string name
+        string description
+        string parent_id FK "Self-referencing"
+        datetime created_at
+        datetime updated_at
+    }
+
+    PRODUCTS {
+        string id PK
+        string name
+        string description
+        decimal price
+        integer stock_quantity
+        string category_id FK
+        string seller_id FK
+        string image_url
+        datetime created_at
+        datetime updated_at
+    }
+
+    ORDERS {
+        string id PK
+        string user_id FK
+        string status
+        decimal total_amount
+        datetime order_date
+        datetime updated_at
+        string shipping_address
+    }
+
+    ORDER_ITEMS {
+        string order_id PK,FK
+        string product_id PK,FK
+        integer quantity
+        decimal unit_price
+        decimal total_price
+    }
+
+    CART_ITEMS {
+        string user_id PK,FK
+        string product_id PK,FK
+        integer quantity
+        datetime added_at
+        datetime updated_at
+    }
+
+    %% User Relationships
+    USERS ||--o{ PRODUCTS : "sells (as seller)"
+    USERS ||--o{ ORDERS : "places (as customer)"
+    USERS ||--o{ CART_ITEMS : "has items in cart"
+
+    %% Category Relationships
+    CATEGORIES ||--o{ PRODUCTS : "contains"
+    CATEGORIES ||--o{ CATEGORIES : "parent-child hierarchy"
+
+    %% Product Relationships
+    PRODUCTS ||--o{ ORDER_ITEMS : "ordered in"
+    PRODUCTS ||--o{ CART_ITEMS : "added to cart"
+
+    %% Order Relationships
+    ORDERS ||--o{ ORDER_ITEMS : "contains items"
+```
+
+## Key Relationship Notes:
+
+### **One-to-Many Relationships:**
+- **Users → Products**: A seller (user) can have many products
+- **Users → Orders**: A customer (user) can have many orders  
+- **Users → Cart Items**: A user can have many items in their cart
+- **Categories → Products**: A category can contain many products
+- **Products → Order Items**: A product can appear in many order items
+- **Products → Cart Items**: A product can be in many users' carts
+- **Orders → Order Items**: An order can contain many order items
+
+### **Self-Referencing Relationship:**
+- **Categories → Categories**: Categories form a hierarchical tree structure where each category can have a parent category
+
+### **Composite Primary Keys:**
+- **Order Items**: `(order_id, product_id)` - Links orders to products with quantities
+- **Cart Items**: `(user_id, product_id)` - Links users to products in their shopping cart
+
+### **Unique Constraints:**
+- **Users**: `username` and `email` must be unique across all users
+
+This entity model supports all 48 access patterns identified in the API analysis, including:
+- User authentication and profile management
+- Product catalog browsing and management
+- Category hierarchy navigation
+- Order processing and history
+- Shopping cart operations
+- Seller-specific functionality
+
+The relationships enable efficient querying for complex operations like:
+- Product searches with category filtering
+- User order history with item details
+- Seller product management
+- Cart validation and checkout processing
+- Category breadcrumb navigation