Herodotus DB

Temporal Databases

There is a lot of academic work about temporal databases. Temporal database theory has two important concepts:

Valid Time
Transaction Time

Valid Time

Valid Time refers to the time when an entity in the real world changed. A valid-time database tracks the history of real-world entities in a database. For example, if you learn a new fact about the history of an entity, you can add that fact to the database. Then you can query the database to learn about the life history of that real-world item.

Transaction Time

Transaction Time refers to the time when a change to the database is made. So you can query what your database looked like at any point in its past.

Herodotus is a Transaction Time system. With Herodotus, you can always see what your data looked like at any point in its past, so you can effectively rewind your data. Herodotus maintains all the historical versions of your data automatically. For example, Herodotus DB applications can use only normal SQL, and you will still get full Transaction Time functionality.

Herodotus is not a Valid Time system. However, for valid-time applications, you can use Herodotus in exactly the same way as you would use any other normal database. For example, to track the history of real-world entities with Herodotus DB, you can create your database tables with a date columns, and make your applications maintain and use those date columns appropriately. Alternatively, you can use specialized languages such as Temporal SQL, and a layer to translate the Temporal SQL into the non-temporal SQL that Herodotus DB understands.