Data Warehouses:

Definition of a Data Warehouse

• Core Concept: A centralized repository that collects information from multiple heterogeneous sources under a single, unified schema.
• Location: It typically resides at a single physical or cloud-based site to simplify access.

1. Clean: Erases errors and noise.
2. Integrate: Merges different data streams together.
3. Transform: Formats data into a unified structure.
4. Load: Populates the centralized warehouse.
5. Refresh: Periodically updates the repository to maintain accuracy.

• Subject-Oriented: Organized around major business subjects (e.g., customer, item, supplier) rather than day-to-day operations.
• Historical Perspective: Stored over longer time horizons (e.g., 6 to 12 months) to track trends.
• Summarized Data: Optimizes performance by pre-aggregating data rather than storing every atomic transaction.
• Multidimensional Modeling: Modeled using Data Cubes, where dimensions represent attributes and cells store aggregated values (like counts or sums) for quick querying.

---