Create data_catalog.md

Author: DataWithBaraa

docs/data_catalog.md

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+# Data Dictionary for Gold Layer
+
+## Overview
+The Gold Layer is the business-level data representation, structured to support analytical and reporting use cases. It consists of **dimension tables** and **fact tables** for specific business metrics.
+
+---
+
+### 1. **gold.dim_customers**
+- **Purpose:** Stores customer details enriched with demographic and geographic data.
+- **Columns:**
+
+| Column Name      | Data Type     | Description                                                                                   |
+|------------------|---------------|-----------------------------------------------------------------------------------------------|
+| customer_key     | INT           | Surrogate key uniquely identifying each customer record in the dimension table.               |
+| customer_id      | INT           | Unique numerical identifier assigned to each customer.                                        |
+| customer_number  | NVARCHAR(50)  | Alphanumeric identifier representing the customer, used for tracking and referencing.         |
+| first_name       | NVARCHAR(50)  | The customer's first name, as recorded in the system.                                         |
+| last_name        | NVARCHAR(50)  | The customer's last name or family name.                                                     |
+| country          | NVARCHAR(50)  | The country of residence for the customer (e.g., 'Australia').                               |
+| marital_status   | NVARCHAR(50)  | The marital status of the customer (e.g., 'Married', 'Single').                              |
+| gender           | NVARCHAR(50)  | The gender of the customer (e.g., 'Male', 'Female', 'n/a').                                  |
+| birthdate        | DATE          | The date of birth of the customer, formatted as YYYY-MM-DD (e.g., 1971-10-06).               |
+| create_date      | DATE          | The date and time when the customer record was created in the system|
+
+---
+
+### 2. **gold.dim_products**
+- **Purpose:** Provides information about the products and their attributes.
+- **Columns:**
+
+| Column Name         | Data Type     | Description                                                                                   |
+|---------------------|---------------|-----------------------------------------------------------------------------------------------|
+| product_key         | INT           | Surrogate key uniquely identifying each product record in the product dimension table.         |
+| product_id          | INT           | A unique identifier assigned to the product for internal tracking and referencing.            |
+| product_number      | NVARCHAR(50)  | A structured alphanumeric code representing the product, often used for categorization or inventory. |
+| product_name        | NVARCHAR(50)  | Descriptive name of the product, including key details such as type, color, and size.         |
+| category_id         | NVARCHAR(50)  | A unique identifier for the product's category, linking to its high-level classification.     |
+| category            | NVARCHAR(50)  | The broader classification of the product (e.g., Bikes, Components) to group related items.  |
+| subcategory         | NVARCHAR(50)  | A more detailed classification of the product within the category, such as product type.      |
+| maintenance_required| NVARCHAR(50)  | Indicates whether the product requires maintenance (e.g., 'Yes', 'No').                       |
+| cost                | INT           | The cost or base price of the product, measured in monetary units.                            |
+| product_line        | NVARCHAR(50)  | The specific product line or series to which the product belongs (e.g., Road, Mountain).      |
+| start_date          | DATE          | The date when the product became available for sale or use, stored in|
+
+---
+
+### 3. **gold.fact_sales**
+- **Purpose:** Stores transactional sales data for analytical purposes.
+- **Columns:**
+
+| Column Name     | Data Type     | Description                                                                                   |
+|-----------------|---------------|-----------------------------------------------------------------------------------------------|
+| order_number    | NVARCHAR(50)  | A unique alphanumeric identifier for each sales order (e.g., 'SO54496').                      |
+| product_key     | INT           | Surrogate key linking the order to the product dimension table.                               |
+| customer_key    | INT           | Surrogate key linking the order to the customer dimension table.                              |
+| order_date      | DATE          | The date when the order was placed.                                                           |
+| shipping_date   | DATE          | The date when the order was shipped to the customer.                                          |
+| due_date        | DATE          | The date when the order payment was due.                                                      |
+| sales_amount    | INT           | The total monetary value of the sale for the line item, in whole currency units (e.g., 25).   |
+| quantity        | INT           | The number of units of the product ordered for the line item (e.g., 1).                       |
+| price           | INT           | The price per unit of the product for the line item, in whole currency units (e.g., 25).      |