> The thing with "Datalog" is that it is really a level of functionality that is implemented in various database query systems and not a well-defined language i

> The thing with "Datalog" is that it is really a level of functionality that is implemented in various database query systems and not a well-defined language in and of itself. 15 years ago I remembered searching for papers about it and did not find so many, now it is hot. Datalog as a language is really just one very specific form of rules (first-order horn implications containing just constants and variables, where each variable in the conclusion also occurs in the premise), and every Datalog program (i.e., every set of rules) is guaranteed to have a finite, universal model. [0] Ceri, Gottlob, Tanca. (1989) What you always wanted to know about Datalog (and never dared to ask). IEEE TRANSACTIONS KNOWLEDGE AND DATA ENGINEERING. [1] Abiteboul, Hull, Vianu. (1994) Foundations of Databases: The Logical Level. Pearson.