Hello! In this section, we will discuss satellites (Satellites), which are an integral part of the Data Vault model. Satellites store business attributes and temporal changes, ensuring data historicity.
What is a satellite?
Satellite is a table linked to a hub or link, which stores descriptive data (attributes) or metadata associated with an entity or relationship.
Satellites allow tracking attribute changes over time and ensuring their historicity.
Basic principles of working with satellites
- Connection to a hub or link:
Each satellite is linked to a hub (for entity attributes) or a link (for relationship attributes). - Historicity:
The satellite records all attribute changes, preserving the start and end dates of data relevance. - Versioning:
Each record in the satellite is unique and reflects the state of attributes at a specific point in time. - Attribute grouping:
Attributes with different change frequencies or data sources should be grouped into separate satellites.
Example: Passenger satellite
Imagine we have a Hub_Passengers hub that stores business keys of passengers. The passenger satellite will contain their attributes, such as surname, date of birth, and contact information.
Structure of Sat_PassengerAttributes
| Hub Key | Surname | Date of Birth | Phone Number | Load Date | End Date | Source System |
|---|---|---|---|---|---|---|
| 1 | Smith | 1990-05-10 | 1234567890 | 2025-01-03 | NULL | BookingSystem |
| 2 | Johnson | 1985-07-20 | 0987654321 | 2025-01-03 | NULL | CRMSystem |
| 1 | Smith | 1990-05-10 | 1122334455 | 2025-01-10 | NULL | FlightSystem |
- Hub Key: Reference to a record in the Hub_Passengers hub.
- Surname: Passenger's surname.
- Date of Birth: Passenger's date of birth.
- Phone Number: Passenger's phone number.
- Load Date: Record load date.
- End Date: Record end date (NULL means the record is current).
- Source System: Data source.
Usage
Supporting changes:
If a passenger's phone number changes, a new version will be added to the satellite:
| Hub Key | Surname | Date of Birth | Phone Number | Load Date | End Date | Source System |
|---|---|---|---|---|---|---|
| 1 | Smith | 1990-05-10 | 1234567890 | 2025-01-03 | 2025-01-10 | BookingSystem |
| 1 | Smith | 1990-05-10 | 1122334455 | 2025-01-10 | NULL | FlightSystem |
Attribute grouping:
Attributes that change rarely (e.g., Date of Birth) can be placed in a separate satellite to optimize data storage.
Advantages of satellites
- Historicity:
Every change is recorded, allowing data analysis for any date in the past. - Flexibility:
Adding new attributes does not affect hubs or links. - Scalability:
Satellites can be split into multiple tables depending on data sources or change frequency.
Conclusion
Satellites make the Data Vault model flexible, resilient to changes, and ready for long-term data storage. They provide full control over change history and allow easy addition of new attributes while maintaining model integrity.