Existential rules allow to assert the existence of not-yet-known individuals. The existential rule framework is also known as an extension to Datalog, called Datalog+/-.
It is particularly relevant to ontology-based query answering. In this framework, a knowledge base is composed of facts —or data— and of ontological knowledge expressed by existential rules (including rules with equality atoms) and negative constraints. The considered queries are conjunctive queries; extending them to unions of conjunctive queries is straightforward.
For a thorough theoretical presentation the visitor is referred to: J.-F. Baget, M. Leclère, M.-L. Mugnier, E. Salvat, On Rules with Existential Variables: Walking the Decidability Line, Artificial Intelligence Journal 175 (2011), pp. 1620-1654. Author's file (pdf).
DLGP (for Datalog Plus) is a textual exchange format at once human-friendly, concise and easy to parse. This format can be seen as an extension of the commonly used format for plain Datalog. A file may contain four kinds of knowledge elements: facts, existential rules, negative constraints and conjunctive queries.
A parser is available.
The source code and associated documentation is available upon request. Please send us an e-mail.
NEW (DLGP Version 2, May 2015)
For compatiblity with Semantic Web languages, a new version of DLGP that allows for IRIs and literals was developed.
A translator from OWL 2 to DLGP Version 2 is also available. For further details,
see the existential rule toolkit Graal.
This tool is dedicated to the analysis of a set of existential rules. It can check if this set belongs to a known decidable class of rules, either directly or by means of its Graph of Rule Dependencies (GRD). Kiabora analyzes the properties of the strongly connected components in the GRD, which allows to determine properties of the rule set with respect to decidability as well as the kind of paradigm (forward or backward chaining) ensuring decidability.
Kiabora is also able to decompose rules into equivalent rules with a simpler head (a single atom or a single piece).
NEW (Kiabora Version 2, Sept. 2015) A new version of KIABORA using DLGP v2 is now available, as a module of the existential rule toolkit Graal.
[More: Kiabora - rule base analyzer]