Question

What are the differences between valid time, transaction time, and bitemporal relations?

Short answer

Valid Time is the time period when a fact is true in real world, Transaction Time represents the time period a fact is stored in the database, and Bitemporal Relations combine both, tracking when a fact was true in real world and when it was stored in the database.

Step-by-step solution

Explain Valid Time

Valid Time is the time period during which a fact is true in the real world. It's represented in the database by two data values, indicating the start and end duration when the data was applicable in the actual world scenario.

Explain Transaction Time

Transaction Time is the time period during which a fact is stored in the database. It’s also represented in the database by two data data values indicating when the data came into the database and when it was deleted or updated.

Explain Bitemporal Relations

Bitemporal Relations combine both Valid Time and Transaction Time. They track both when a fact was true in real world and when it was stored in the database. Bitemporal data is stored in a bitemporal table that includes both valid time and transaction time columns for keeping this dual period information.

Key concepts

Understanding Valid Time in Databases

Valid Time is a concept used in temporal databases to indicate the time period during which a particular fact is considered true in the real world. Imagine that you have a database recording employment data. The valid time would represent when an employee was actually employed at a company, from the start date of employment to the end date.

• Start and End Points: Valid time is defined by two data points—the start time and the end time. These points specify the exact duration during which the fact is true in the real world.
• Real-World Truth: Valid time reflects the real-world status of information, separate from the time it is recorded in the database.

Valid time helps maintain historical accuracy about facts, such as ensuring an employee's history of employment is captured accurately even if the record in the database is updated.

Exploring Transaction Time in Temporal Databases

Transaction Time is the period during which a fact is stored in the database, tracking its existence within the system. This concept is crucial for understanding the history of data operations, such as when a new entry is made or when data gets updated or deleted.

• Database Storage: Transaction time spans from the moment data is inserted into the database until it is no longer part of the current dataset, such as when it's deleted or amended.
• Immutable Records: In many databases, transaction time data is immutable, meaning once it's recorded, it cannot be altered to ensure an accurate log of data operations.

By tracking transaction time, databases can maintain a complete log of all the changes applied to the data, facilitating rollback to previous states or auditing changes over time.

The Role of Bitemporal Relations

Bitemporal Relations merge both valid time and transaction time, becoming a powerful tool for managing and analyzing data. They allow databases to track both when a fact was true in reality and when it was recorded in the system.

• Dual Time Tracking: Bitemporal tables contain columns for both valid and transaction times, providing a comprehensive view of the data's lifespan and history.
• Historical and Operational Insights: These relations are invaluable for auditing purposes and for gaining insights into how data has evolved in reality compared to its recorded history.

This dual perspective helps manage complex data requirements, such as tracking policy changes over time or maintaining detailed version histories of records. Bitemporal relations are thus integral to creating robust, historical, and audit-compliant systems.