Answer Counting under Guarded TGDs

01/08/2021
by   Cristina Feier, et al.
0

We study the complexity of answer counting for ontology-mediated queries and for querying under constraints, considering conjunctive queries and unions thereof (UCQs) as the query language and guarded TGDs as the ontology and constraint language, respectively. Our main result is a classification according to whether answer counting is fixed-parameter tractable (FPT), W[1]-equivalent, #W[1]-equivalent, #W[2]-hard, or #A[2]-equivalent, lifting a recent classification for UCQs without ontologies and constraints due to Dell et al. The classification pertains to various structural measures, namely treewidth, contract treewidth, starsize, and linked matching number. Our results rest on the assumption that the arity of relation symbols is bounded by a constant and, in the case of ontology-mediated querying, that all symbols from the ontology and query can occur in the data (so-called full data schema). We also study the meta-problems for the mentioned structural measures, that is, to decide whether a given ontology-mediated query or constraint-query specification is equivalent to one for which the structural measure is bounded.

READ FULL TEXT

page 1

page 2

page 3

page 4

research
12/28/2019

The Limits of Efficiency for Open- and Closed-World Query Evaluation Under Guarded TGDs

Ontology-mediated querying and querying in the presence of constraints a...
research
04/29/2019

A Complete Classification of the Complexity and Rewritability of Ontology-Mediated Queries based on the Description Logic EL

We provide an ultimately fine-grained analysis of the data complexity an...
research
04/18/2018

Dichotomies in Ontology-Mediated Querying with the Guarded Fragment

We study the complexity of ontology-mediated querying when ontologies ar...
research
01/27/2021

Characterising Fixed Parameter Tractability of Query Evaluation over Guarded TGDs

We study the parameterized complexity of evaluating Ontology Mediated Qu...
research
11/22/2021

Forbidden Substructures for Tractable Conjunctive Query Answering with Degree 2

We study the tractability of conjunctive query answering for queries wit...
research
01/23/2014

Reasoning over Ontologies with Hidden Content: The Import-by-Query Approach

There is currently a growing interest in techniques for hiding parts of ...
research
02/13/2019

Counting Answers to Existential Questions

Conjunctive queries select and are expected to return certain tuples fro...

Please sign up or login with your details

Forgot password? Click here to reset