---
title: "Efficient Reasoning in Proper Knowledge Bases with Unknown Individuals"
authors:
  - "Giuseppe De Giacomo"
  - "Yves Lespérance"
  - "Hector J. Levesque"
doi: "10.5591/978-1-57735-516-8/IJCAI11-144"
url: "https://ijcai.org/proceedings/2011/144"
pdf: "https://ijcai.org/proceedings/2011/0144.pdf"
venue: "Proceedings of the Twenty-Second International Joint Conference on Artificial Intelligence"
year: 2011
pages: "827-831"
track: ""
keywords:
---

# Efficient Reasoning in Proper Knowledge Bases with Unknown Individuals

Giuseppe De Giacomo, Yves Lespérance, Hector J. Levesque

*Proceedings of the Twenty-Second International Joint Conference on Artificial Intelligence*, pages 827-831. DOI: [10.5591/978-1-57735-516-8/IJCAI11-144](https://doi.org/10.5591/978-1-57735-516-8/IJCAI11-144)

## Abstract

This work develops an approach to efficient reasoning in first-order knowledge bases with incomplete information. We build on Levesque's proper knowledge bases approach, which supports limited incomplete knowledge in the form of a possibly infinite set of positive or negative ground facts. We propose a generalization which allows these facts to involve unknown individuals, as in the work on labeled null values in databases. Dealing with such unknown individuals has been shown to be a key feature in the database literature on data integration and data exchange. In this way, we obtain one of the most expressive first-order open-world settings for which reasoning can still be done efficiently by evaluation, as in relational databases. We show the soundness of the reasoning procedure and its completeness for queries in a certain normal form.