Inconsistency-tolerant Query Answering in Ontology-based Data Access

Ontology-based data access (OBDA) is receiving great attention as a new paradigm for managing information systems through semantic technologies. According to this paradigm, a Description Logic ontology provides an abstract and formal representation of the domain of interest to the information system, and is used as a sophisticated schema for accessing the data and formulating queries over them. In this paper, we address the problem of dealing with inconsistencies in OBDA. Our general goal is both to study DL semantical frameworks that are inconsistency-tolerant, and to devise techniques for answering unions of conjunctive queries under such inconsistency-tolerant semantics. Our work is inspired by the approaches to consistent query answering in databases, which are based on the idea of living with inconsistencies in the database, but trying to obtain only consistent information during query answering, by relying on the notion of database repair. We first adapt the notion of database repair to our context, and show that, according to such a notion, inconsistency-tolerant query answering is intractable, even for very simple DLs. Therefore, we propose a different repair-based semantics, with the goal of reaching a good compromise between the expressive power of the semantics and the computational complexity of inconsistency-tolerant query answering. Indeed, we show that query answering under the new semantics is first-order rewritable in OBDA, even if the ontology is expressed in one of the most expressive members of the DL-Lite family

Consistent Query Answers in the Presence of Universal Constraints

The framework of consistent query answers and repairs has been introduced to alleviate the impact of inconsistent data on the answers to a query. A repair is a minimally different consistent instance and an answer is consistent if it is present in every repair. In this article we study the complexity of consistent query answers and repair checking in the presence of universal constraints. We propose an extended version of the conflict hypergraph which allows to capture all repairs w.r.t. a set of universal constraints. We show that repair checking is in PTIME for the class of full tuple-generating dependencies and denial constraints, and we present a polynomial repair algorithm. This algorithm is sound, i.e. always produces a repair, but also complete, i.e. every repair can be constructed. Next, we present a polynomial-time algorithm computing consistent answers to ground quantifier-free queries in the presence of denial constraints, join dependencies, and acyclic full-tuple generating dependencies. Finally, we show that extending the class of constraints leads to intractability. For arbitrary full tuple-generating dependencies consistent query answering becomes coNP-complete. For arbitrary universal constraints consistent query answering is \Pi_2^p-complete and repair checking coNP-complete.Comment: Submitted to Information System

Inconsistency-Tolerant Integrity Checking

All methods for efficient integrity checking require all integrity constraints to be totally satisfied, before any update is executed. However, a certain amount of inconsistency is the rule, rather than the exception in databases. In this paper, we close the gap between theory and practice of integrity checking, i.e., between the unrealistic theoretical requirement of total integrity and the practical need for inconsistency tolerance, which we define for integrity checking methods. We show that most of them can still be used to check whether updates preserve integrity, even if the current state is inconsistent. Inconsistency-tolerant integrity checking proves beneficial both for integrity preservation and query answering. Also, we show that it is useful for view updating, repairs, schema evolution, and other applications.Hendrik Decker has been supported by FEDER and the Spanish MEC grant TIN2006-14738-C02-01. Davide Martinenghi has been supported by the Search Computing (SeCo) project, funded by ERC under the 2008 Call for "IDEAS Advanced Grants." The authors also wish to thank Davide Barbieri for his valuable contribution to the experimental evaluation.Decker, H.; Martinenghi, D. (2011). Inconsistency-Tolerant Integrity Checking. IEEE Transactions on Knowledge and Data Engineering. 23(2):218-234. https://doi.org/10.1109/TKDE.2010.87S21823423

Dealing with Inconsistency and Incompleteness in Data Integration

Marco Schaerf, Giuseppe Di Battista, Domenico SaccÃ

Inconsistency Handling in Prioritized Databases with Universal Constraints: Complexity Analysis and Links with Active Integrity Constraints

This paper revisits the problem of repairing and querying inconsistent databases equipped with universal constraints. We adopt symmetric difference repairs, in which both deletions and additions of facts can be used to restore consistency, and suppose that preferred repair actions are specified via a binary priority relation over (negated) facts. Our first contribution is to show how existing notions of optimal repairs, defined for simpler denial constraints and repairs solely based on fact deletion, can be suitably extended to our richer setting. We next study the computational properties of the resulting repair notions, in particular, the data complexity of repair checking and inconsistency-tolerant query answering. Finally, we clarify the relationship between optimal repairs of prioritized databases and repair notions introduced in the framework of active integrity constraints. In particular, we show that Pareto-optimal repairs in our setting correspond to founded, grounded and justified repairs w.r.t. the active integrity constraints obtained by translating the prioritized database. Our study also yields useful insights into the behavior of active integrity constraints.Comment: This is an extended version of a paper appearing at the 20th International Conference on Principles of Knowledge Representation and Reasoning (KR 2023). 28 page