Learn Datalog Today is an interactive tutorial designed to teach you the Datomic dialect of Datalog. Datalog is a declarative database query language with roots in logic programming. Datalog has similar expressive power as SQL.
Datomic is a new database with an interesting and novel architecture, giving its users a unique set of features. You can read more about Datomic at http://datomic.com and the architecture is described in some detail in this InfoQ article.