{"type":"ScholarlyArticle","title":"Tractable Fragments of Datalog with Metric Temporal Operators","authors":[{"name":"Przemysław A. Wałęga","slug":"przemys-aw-a-wa-ega","given":"Przemysław A.","family":"Wałęga","affiliation":"Department of Computer Science , University of Oxford , UK"},{"name":"Bernardo Cuenca Grau","slug":"bernardo-cuenca-grau","given":"Bernardo Cuenca","family":"Grau","affiliation":"Department of Computer Science , University of Oxford , UK"},{"name":"Mark Kaminski","slug":"mark-kaminski","given":"Mark","family":"Kaminski","affiliation":"Department of Computer Science , University of Oxford , UK"},{"name":"Egor V. Kostylev","slug":"egor-v-kostylev","given":"Egor V.","family":"Kostylev","affiliation":"Department of Computer Science , University of Oxford , UK"}],"abstract":"We study the data complexity of  reasoning for several fragments of MTL - an extension of Datalog with metric temporal operators over the rational numbers. Reasoning in the full MTL language is PSPACE-complete, which handicaps its application in practice. To achieve tractability we first study the core fragment, which disallows conjunction in rule bodies, and show that reasoning remains PSPACE-hard. Intractability prompts us to also limit the kinds of temporal operators allowed in rules, and we propose a practical core fragment for which reasoning becomes TC0-complete. Finally, we show that this fragment can be extended by allowing linear conjunctions in rule bodies, where at most one atom can be intensional (IDB); we show that the resulting fragment is NL-complete, and hence no harder than plain linear Datalog.","doi":"10.24963/ijcai.2020/266","url":"https://ijcai.org/proceedings/2020/266","pdf":"https://ijcai.org/proceedings/2020/0266.pdf","markdown":"https://ijcai.org/proceedings/2020/266.md","bibtex":"https://ijcai.org/proceedings/2020/bibtex/266","volume":{"slug":"2020","title":"Proceedings of the Twenty-Ninth International Joint Conference on Artificial Intelligence","short_title":"IJCAI 2020","url":"https://ijcai.org/proceedings/2020/","year":2020,"location":"Yokohama","dates":"January 2021 (postponed from 11-17 July 2020)","editors":"Christian Bessiere","isbn":"978-0-9992411-6-5","publisher":"International Joint Conferences on Artificial Intelligence Organization","doi_prefix":"10.24963/ijcai.2020"},"section":"Knowledge Representation and Reasoning","track":"Main track","number":266,"pages":{"first":1919,"last":1925},"keywords":["Knowledge Representation and Reasoning: Qualitative, Geometric, Spatial, Temporal Reasoning","Knowledge Representation and Reasoning: Computational Complexity of Reasoning","Knowledge Representation and Reasoning: Logics for Knowledge Representation"],"videos":[{"label":"Video","url":"https://videos.ijcai20.org/26968/file_26968.m3u8","length_sec":886,"provider":"hls"}],"references":[{"position":1,"raw":"[Abiteboul et al., 1995] Serge Abiteboul, Richard Hull, and Victor Vianu. 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