Datascript is based on the Datomic DB created by Cognitect.
Datomic's query and rules system is an extended form of Datalog. Datalog is a deductive query system, typically consisting of:
- A database of facts
- A set of rules for deriving new facts from existing facts
- A query processor that, given some partial specification of a fact or rule: finds all instances of that specification implied by the database and rules i.e. all the matching facts
The data model in Datascript/Datomic is based around atomic facts called datoms. A datom is a 4-tuple consisting of:
- Entity ID
- Attribute
- Value
- Transaction ID
Example:
[<e-id> <attribute> <value> <tx-id>]
...
[ 167 :person/id 168373838 102 ]
[ 167 :person/name "James Cameron" 102 ]
...
[ 234 :movie/id 173532083 102 ]
[ 234 :movie/title "Die Hard" 103 ]
[ 234 :movie/year 1987 103 ]
The following query finds all entity-ids that have the attribute :person/namewith a value of "Ridley Scott":
[:find ?e
:where
[?e :person/name "Ridley Scott"]]