# How to Approximate Ontology-Mediated Queries

arXiv: https://arxiv.org/abs/2107.05369 · HTML: https://mlsanity.com/paper/2107.05369/

## Key facts

- Cited by 2 papers in the map (data through 14 Oct 2026).
- Builds on 7 of its 59 references that are in the map.
- First posted on arXiv 12 Jul 2021.

## Builds on (most cited first, 7 of 7)

- [Ontology-based Data Access: A Study through Disjunctive Datalog, CSP, and MMSNP](https://mlsanity.com/paper/1301.6479/) (2013)
- [Rewritability in Monadic Disjunctive Datalog, MMSNP, and Expressive Description Logics](https://mlsanity.com/paper/1701.02231/) (2017)
- [A More General Theory of Static Approximations for Conjunctive Queries](https://mlsanity.com/paper/1904.00934/) (2019)
- [A Journey into Ontology Approximation: From Non-Horn to Horn](https://mlsanity.com/paper/2001.07754/) (2020)
- [When is Ontology-Mediated Querying Efficient?](https://mlsanity.com/paper/2003.07800/) (2020)
- [The Data Complexity of Description Logic Ontologies](https://mlsanity.com/paper/1611.02453/) (2016)
- [Dichotomies in Ontology-Mediated Querying with the Guarded Fragment](https://mlsanity.com/paper/1804.06894/) (2018)

## Built on by (most cited first, 2 of 2)

- [Ontology-Mediated Querying on Databases of Bounded Cliquewidth](https://mlsanity.com/paper/2205.02190/) (2022)
- [Description Logics with Abstraction and Refinement](https://mlsanity.com/paper/2306.03717/) (2023)

## Abstract (arXiv)

We introduce and study several notions of approximation for ontology-mediated queries based on the description logics ALC and ALCI. Our approximations are of two kinds: we may (1) replace the ontology with one formulated in a tractable ontology language such as ELI or certain TGDs and (2) replace the database with one from a tractable class such as the class of databases whose treewidth is bounded by a constant. We determine the computational complexity and the relative completeness of the resulting approximations. (Almost) all of them reduce the data complexity from coNP-complete to PTime, in some cases even to fixed-parameter tractable and to linear time. While approximations of kind (1) also reduce the combined complexity, this tends to not be the case for approximations of kind (2). In some cases, the combined complexity even increases.