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docs/01-overview.md

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+# Hotel Reservations — Data Warehouse Project
+
+## Project Summary
+
+This project implements a complete **Data Warehousing pipeline** for a hotel reservation system, covering all standard DW layers:
+
+```
+MySQL OLTP  ──►  Apache NiFi ETL  ──►  Oracle Data Mart  ──►  Power BI Reports
+(source)          (transform)           (analytical store)      (OLAP queries)
+```
+
+The system is built around the **A.24 Hotel Reservations** domain from the course specification. The OLTP database was populated with **~635,000 synthetically generated rows** covering 200 hotels, 100,000 guests, 500,000 bookings, and 531,000 room bookings across a 4-year period (2022–2025).
+
+---
+
+## Business Context
+
+A hotel chain needs to answer questions like:
+
+- Which countries generate the most revenue per quarter?
+- How does occupancy differ between peak and off-peak seasons?
+- What is the revenue contribution of 5-star vs 3-star hotels?
+- How has a hotel's revenue changed after upgrading its star rating?
+
+These questions require **historical, multi-dimensional analysis** that a normalized OLTP database cannot serve efficiently. The data mart provides pre-modelled, denormalized data optimized for analytical queries.
+
+---
+
+## Architecture
+
+```
+┌─────────────────────────────────────────────────────────┐
+│  SOURCE LAYER                                           │
+│  MySQL 8.4  (Docker/Podman, port 13306)                 │
+│  Database: hotel_reservations                           │
+│  13 normalized tables, ~635K rows                       │
+└───────────────────────┬─────────────────────────────────┘
+                        │ JDBC (MySqlConnector)
+                        ▼
+┌─────────────────────────────────────────────────────────┐
+│  ETL LAYER                                              │
+│  Apache NiFi                                            │
+│  5 Process Groups: Date Dim / Static Dims /             │
+│  SCD2 Hotel / SCD1 Guest / Incremental Fact             │
+└───────────────────────┬─────────────────────────────────┘
+                        │ JDBC (Oracle JDBC)
+                        ▼
+┌─────────────────────────────────────────────────────────┐
+│  DATA MART LAYER                                        │
+│  Oracle (university lab schema)                         │
+│  Star schema: 6 dimensions + 1 fact table               │
+│  SCD Type 2 on DIM_HOTEL                                │
+└───────────────────────┬─────────────────────────────────┘
+                        │
+                        ▼
+┌─────────────────────────────────────────────────────────┐
+│  PRESENTATION LAYER                                     │
+│  Power BI Desktop                                       │
+│  OLAP reports via DirectQuery / Import                  │
+└─────────────────────────────────────────────────────────┘
+```
+
+---
+
+## Technology Stack
+
+| Component | Technology | Version |
+|-----------|-----------|---------|
+| OLTP Database | MySQL | 8.4 |
+| Container runtime | Docker / Podman | — |
+| Data generator | C# (.NET) | 10 |
+| ETL tool | Apache NiFi | — |
+| Data Mart | Oracle RDBMS | university lab |
+| Reporting | Power BI Desktop | — |
+
+---
+
+## Repository Structure
+
+```
+IPZ_1/
+├── docker/
+│   ├── start.sh          # Start MySQL container (Linux/macOS)
+│   ├── stop.sh           # Stop MySQL container
+│   ├── start.ps1         # Start MySQL container (Windows)
+│   └── stop.ps1          # Stop MySQL container
+├── sql/
+│   ├── schema.sql        # MySQL OLTP DDL
+│   └── datamart_schema.sql  # Oracle Data Mart DDL
+├── generator/
+│   └── generate.cs       # .NET 10 data generator script
+└── docs/
+    ├── 01-overview.md    # This file
+    ├── 02-oltp.md        # OLTP database design
+    ├── 03-datamart.md    # Data mart design
+    ├── 04-setup.md       # Setup and run guide
+    └── nifi-flow.md      # NiFi ETL flow reference
+```