Data model

Noblit stores datoms. Datoms assert or retract attributes of entities. For example, entity 12 might have an attribute user.email with value rachael@tyrell.com. Conceptually, the database is an append-only log of (entity, attribute, value) tuples, together with the time at which they were asserted or retracted in the form of a transaction id. A view of the database at a given point in time is the set of all (entity, attribute, value) tuples that have been asserted and not retracted before or at that time.

A datom is a tuple of the following five values:

• Entity: An integer that uniquely identifies an entity in the database.
• Attribute: Analogous to a column in a relational database.
• Value: The value for the attribute.
• Transaction: The transaction id of the transaction that added the datom.
• Operation: Either assert or retract.

To get a view of the database at a given transaction t, we exclude all datoms with a transaction greater than t. Then we cancel assertions against subsequent retractions. What is left is the set of (entity, attribute, value) tuples that were true after transaction t.