barbagrigia / datascript-tutorial

Datascript and Datomic tutorial book

Datascript

Datascript is based on the Datomic DB created by Cognitect.

Datalog

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

Data model

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"]]

Useful resources

Learn datalog queries