Incomplete Information in Relational Databases
Journal of the ACM (JACM)
On the integrity of databases with incomplete information
PODS '86 Proceedings of the fifth ACM SIGACT-SIGMOD symposium on Principles of database systems
On the relative expressiveness of description logics and predicate logics
Artificial Intelligence
The complexity of querying indefinite data about linearly ordered domains
Journal of Computer and System Sciences - Special issue: dedicated to the memory of Paris Kanellakis
On the decidability of query containment under constraints
PODS '98 Proceedings of the seventeenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
Combining Horn rules and description logics in CARIN
Artificial Intelligence
Data integration: a theoretical perspective
Proceedings of the twenty-first ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Foundations of Databases: The Logical Level
Foundations of Databases: The Logical Level
Querying the Semantic Web: A Formal Approach
ISWC '02 Proceedings of the First International Semantic Web Conference on The Semantic Web
The complexity of relational query languages (Extended Abstract)
STOC '82 Proceedings of the fourteenth annual ACM symposium on Theory of computing
The description logic handbook: theory, implementation, and applications
The description logic handbook: theory, implementation, and applications
Description logics for databases
The description logic handbook
A possible simplification of the semantic web architecture
Proceedings of the 13th international conference on World Wide Web
Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Characterizing data complexity for conjunctive query answering in expressive description logics
AAAI'06 Proceedings of the 21st national conference on Artificial intelligence - Volume 1
DL-Lite: tractable description logics for ontologies
AAAI'05 Proceedings of the 20th national conference on Artificial intelligence - Volume 2
IJCAI'05 Proceedings of the 19th international joint conference on Artificial intelligence
Aggregate queries over ontologies
Proceedings of the 2nd international workshop on Ontologies and information systems for the semantic web
On Combining Description Logic Ontologies and Nonrecursive Datalog Rules
RR '08 Proceedings of the 2nd International Conference on Web Reasoning and Rule Systems
Exploiting conjunctive queries in description logic programs
Annals of Mathematics and Artificial Intelligence
Conjunctive query answering for the description logic SHIQ
Journal of Artificial Intelligence Research
Deciding Query Entailment for Fuzzy $\mathcal{SHIN}$ Ontologies
ASWC '09 Proceedings of the 4th Asian Conference on The Semantic Web
Nominals, inverses, counting, and conjunctive queries or: why infinity is your friend!
Journal of Artificial Intelligence Research
Journal of Computer and System Sciences
Proceedings of the VLDB Endowment
An update on query answering with restricted forms of negation
RR'12 Proceedings of the 6th international conference on Web Reasoning and Rule Systems
Data complexity of query answering in description logics
Artificial Intelligence
Conjunctive queries with negation over DL-Lite: a closer look
RR'13 Proceedings of the 7th international conference on Web Reasoning and Rule Systems
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We study query answering in Description Logics (DLs). In particular, we consider conjunctive queries, unions of conjunctive queries, and their extensions with safe negation or inequality, which correspond to well-known classes of relational algebra queries. We provide a set of decidability, undecidability and complexity results for answering queries of the above languages over various classes of Description Logics knowledge bases. In general, such results show that extending standard reasoning tasks in DLs to answering relational queries is unfeasible in many DLs, even in inexpressive ones. In particular: (i) answering even simple conjunctive queries is undecidable in some very expressive DLs in which standard DL reasoning is decidable; (ii) in DLs where answering (unions of) conjunctive queries is decidable, adding the possibility of expressing safe negation or inequality leads in general to undecidability of query answering, even in DLs of very limited expressiveness. We also highlight the negative consequences of these results for the integration of ontologies and rules. We believe that these results have important implications for ontology-based information access, in particular for the design of query languages for ontologies.