What is data warehousing and ETL?

Question

Accepted Answer

**Data Warehouse** — centralized repository for analytical data. **ETL** — Extract, Transform, Load.

**Data Warehouse:**
- Subject-oriented.
- Integrated from multiple sources.
- Time-variant (historical).
- Non-volatile (read-only).

**ETL Process:**
```
1. Extract: Pull data from sources
   - CRM, ERP, flat files, APIs
2. Transform: Clean and convert
   - Data cleaning, format conversion
   - Aggregation, deduplication
3. Load: Insert into warehouse
   - Full load or incremental
   - Scheduled or real-time
```

**ETL Tools:**
- Apache Spark, Talend, Informatica.
- dbt (data build tool).
- AWS Glue, Azure Data Factory.

**Benefits:** Centralized data, historical analysis, data quality.

Systems Analyst: What is data warehousing and ETL?