{"type":"ScholarlyArticle","title":"Expressivity of Datalog Variants - Completing the Picture","authors":[{"name":"Sebastian Rudolph","slug":"sebastian-rudolph","given":"Sebastian","family":"Rudolph","affiliation":""},{"name":"Michaël Thomazo","slug":"michael-thomazo","given":"Michael","family":"Thomazo","affiliation":""}],"abstract":"Computational and model-theoretic properties of logical languages constitute a central field of research in logic-based knowledge representation. Datalog is a very popular formalism, a de-facto standard for expressing and querying knowledge. Diverse results exist regarding the expressivity of Datalog and its extension by input negation (semipositive Datalog) and/or a linear order (order-invariant Datalog). When classifying the expressivity of logical formalisms by their model-theoretic properties, a very natural and prominent such property is preservation under homomorphisms. This paper solves the remaining open questions needed to arrive at a complete picture regarding the interrelationships between the class of homomorphism-closed queries and the query classes related to the four versions of Datalog. Most notably, we exhibit a query that is both homomorphism-closed and computable in polynomial time but cannot be expressed in order-invariant Datalog.","doi":null,"url":"https://ijcai.org/proceedings/2016/178","pdf":"https://ijcai.org/proceedings/2016/0178.pdf","markdown":"https://ijcai.org/proceedings/2016/178.md","bibtex":"https://ijcai.org/proceedings/2016/bibtex/178","volume":{"slug":"2016","title":"Proceedings of the Twenty-Fifth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2016","url":"https://ijcai.org/proceedings/2016/","year":2016,"location":"New York, NY, USA","dates":"9–15 July 2016","editors":"Subbarao Kambhampati","isbn":"978-1-57735-770-4; 978-1-57735-771-1","publisher":"AAAI Press / International Joint Conferences on Artificial Intelligence","doi_prefix":""},"section":null,"track":"","number":178,"pages":{"first":1230,"last":1235},"keywords":[],"videos":[],"references":[],"license_note":"Copyright International Joint Conferences on Artificial Intelligence."}