Data model#

Datoms#

VevDB stores facts as datoms:

entity attribute value transaction added?

• entity is a stable integer ID.
• attribute is a keyword.
• value is a scalar or tuple.
• transaction identifies the transaction.
• added? distinguishes assertions from retractions in history.

Current state is the set of assertions not later retracted.

Database values#

A database value is an immutable snapshot. Reads take a database value, not a live connection.

(def before (d/db conn))
(d/transact conn [{:db/id 1 :person/name "Ada"}])
(def after (d/db conn))

before does not change when the transaction commits.

A connection owns the current database value and serializes writes. db-with applies a transaction to a database value without changing a connection.

Values#

Stored values include:

• strings
• integers and floats
• booleans
• keywords and symbols
• references
• instants
• UUIDs
• tuples

Maps and sets structure transactions and query inputs. They are not stored as datom values. Cardinality-many collections become separate datoms.

Schema#

Schema is stored as datoms on entities with :db/ident.

Supported schema properties include:

• :db/valueType
• :db/cardinality
• :db/unique
• :db/isComponent
• tuple attributes

Example:

{:db/ident :person/email
 :db/valueType :db.type/string
 :db/cardinality :db.cardinality/one
 :db/unique :db.unique/identity}

VevDB also accepts schemaless attributes.

Indexes#

Database values expose four datom indexes:

• EAVT: entity, attribute, value, transaction
• AEVT: attribute, entity, value, transaction
• AVET: attribute, value, entity, transaction
• VAET: reference value, attribute, entity, transaction

The public APIs include datoms, seek-datoms, rseek-datoms, and index-range.

See Transactions, Queries and pull, and History.