diff --git a/README.md b/README.md
index 9218408..00bec0f 100644
--- a/README.md
+++ b/README.md
@@ -40,28 +40,80 @@ A web application for tracking grocery prices and shopping events. Built with Fa
 
 ## Data Model
 
-### Groceries
-- `id`: Primary key
-- `name`: Grocery name
-- `price`: Current price
-- `category`: Food category
-- `organic`: Boolean flag
-- `weight`: Weight/volume
-- `weight_unit`: Unit (g, kg, ml, l, piece)
+### Core Entities
 
-### Shops
-- `id`: Primary key
-- `name`: Shop name
-- `city`: Location city
-- `address`: Optional full address
+#### Groceries (`groceries` table)
+- `id`: Integer, Primary key, Auto-increment
+- `name`: String, Grocery name (indexed, required)
+- `category`: String, Food category (required)
+- `organic`: Boolean, Organic flag (default: false)
+- `weight`: Float, Weight/volume (optional)
+- `weight_unit`: String, Unit of measurement (default: "piece")
+  - Supported units: "g", "kg", "ml", "l", "piece"
+- `created_at`: DateTime, Creation timestamp (auto-generated)
+- `updated_at`: DateTime, Last update timestamp (auto-updated)
 
-### Shopping Events
-- `id`: Primary key
-- `shop_id`: Foreign key to shops
-- `date`: Purchase date
-- `total_amount`: Optional total cost
-- `notes`: Optional notes
-- `groceries`: Many-to-many relationship with amounts
+#### Shops (`shops` table)
+- `id`: Integer, Primary key, Auto-increment
+- `name`: String, Shop name (indexed, required)
+- `city`: String, Location city (required)
+- `address`: String, Full address (optional)
+- `created_at`: DateTime, Creation timestamp (auto-generated)
+
+#### Shopping Events (`shopping_events` table)
+- `id`: Integer, Primary key, Auto-increment
+- `shop_id`: Integer, Foreign key to shops (required)
+- `date`: DateTime, Purchase date (required, default: current time)
+- `total_amount`: Float, Total cost of shopping event (optional, auto-calculated)
+- `notes`: String, Optional notes about the purchase
+- `created_at`: DateTime, Creation timestamp (auto-generated)
+
+### Association Table
+
+#### Shopping Event Groceries (`shopping_event_groceries` table)
+Many-to-many relationship between shopping events and groceries with additional data:
+- `id`: Integer, Primary key, Auto-increment
+- `shopping_event_id`: Integer, Foreign key to shopping_events (required)
+- `grocery_id`: Integer, Foreign key to groceries (required)
+- `amount`: Float, Quantity purchased in this event (required, > 0)
+- `price`: Float, Price at time of purchase (required, ≥ 0)
+
+### Relationships
+
+```
+┌─────────────────┐         ┌─────────────────────────────┐         ┌─────────────────┐
+│     Shops       │         │  Shopping Event Groceries   │         │   Groceries     │
+│                 │         │     (Association Table)     │         │                 │
+│ • id            │ ←──────→│ • shopping_event_id         │ ←──────→│ • id            │
+│ • name          │  1:N    │ • grocery_id                │  N:M    │ • name          │
+│ • city          │         │ • amount                    │         │ • category      │
+│ • address       │         │ • price                     │         │ • organic       │
+│ • created_at    │         │                             │         │ • weight        │
+└─────────────────┘         └─────────────────────────────┘         │ • weight_unit   │
+         │                                  │                       │ • created_at    │
+         │                                  │                       │ • updated_at    │
+         │ 1:N                              │                       └─────────────────┘
+         ▼                                  │
+┌─────────────────┐                         │
+│ Shopping Events │ ←───────────────────────┘
+│                 │          1:N
+│ • id            │
+│ • shop_id       │
+│ • date          │
+│ • total_amount  │
+│ • notes         │
+│ • created_at    │
+└─────────────────┘
+```
+
+### Key Features
+
+- **Price History**: Each grocery purchase stores the price at that time, enabling price tracking
+- **Flexible Quantities**: Support for decimal amounts (e.g., 1.5 kg of apples)
+- **Auto-calculation**: Total amount can be automatically calculated from individual items
+- **Free Items**: Supports items with price 0 (samples, promotions, etc.)
+- **Audit Trail**: All entities have creation timestamps for tracking
+- **Data Integrity**: Foreign key constraints ensure referential integrity
 
 ## Setup Instructions