15

Forgetting for Logic Programs/Existential Rules
           (Abstract of Invited Talk)

                  Kewen Wang (collaboration with Zhe Wang)

                            Griffith University, Australia


The notion of forgetting has been investigated extensively for various types of
logic programs. Syntactically, a logic program can be Horn, normal (non- dis-
junctive), disjunctive, nested and existential. The semantics for most of such
logic programs is based on either classical semantics or stable models. In this
talk, we will discuss some major approaches to forgetting in logic programming,
especially, the class of existential rules, a family of expressive ontology languages,
which inherit desired expressive and reasoning properties from both description
logics and logic programming. Yet it is challenging to establish a theory of forget-
ting for existential rules. We will introduce a theory of forgetting for existential
rules in terms of query answering based a novel notion of unfolding. A result of
forgetting may not be expressible in existential rules, and we then capture the
expressibility of forgetting by a variant of boundedness. While the expressibility
is undecidable in general, we identify a decidable fragment. Finally, we provide
an algorithm for forgetting in this fragment.




Copyright c 2017 by the paper’s authors
In: P. Koopmann, S. Rudolph, R. Schmidt, C. Wernhard (eds.): SOQE 2017 – Pro-
ceedings of the Workshop on Second-Order Quantifier Elimination and Related Topics,
Dresden, Germany, December 6–8, 2017, published at http://ceur-ws.org.