scholarly journals Horn-Rewritability vs PTime Query Evaluation in Ontology-Mediated Querying

2018 ◽  
Author(s):  
Andre Hernich ◽  
Carsten Lutz ◽  
Fabio Papacchini ◽  
Frank Wolter
Keyword(s):  
Description Logic ◽  
Query Evaluation ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Natural Variations ◽  
Horn Fragment ◽  
The Relationship

In ontology-mediated querying with an expressive description logic L, two desirable properties of a TBox T are (1) being able to replace T with a TBox formulated in the Horn-fragment of L without affecting the answers to conjunctive queries, and (2) that every conjunctive query can be evaluated in PTime w.r.t. T. We investigate in which cases (1) and (2) are equivalent, finding that the answer depends on whether the unique name assumption (UNA) is made, on the description logic under consideration, and on the nesting depth of quantifiers in the TBox. We also clarify the relationship between query evaluation with and without UNA and consider natural variations of property (1).

scholarly journals Conjunctive Query Answering for the Description Logic SHIQ

2008 ◽  
Vol 31 ◽  
pp. 157-204 ◽  
Author(s):  
B. Glimm ◽  
C. Lutz ◽  
I. Horrocks ◽  
U. Sattler
Keyword(s):  
Description Logic ◽  
Query Language ◽  
Description Logics ◽  
Knowledge Bases ◽  
Deterministic Algorithm ◽  
Query Answering ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Complexity Bounds ◽  
Double Exponential

Conjunctive queries play an important role as an expressive query language for Description Logics (DLs). Although modern DLs usually provide for transitive roles, conjunctive query answering over DL knowledge bases is only poorly understood if transitive roles are admitted in the query. In this paper, we consider unions of conjunctive queries over knowledge bases formulated in the prominent DL SHIQ and allow transitive roles in both the query and the knowledge base. We show decidability of query answering in this setting and establish two tight complexity bounds: regarding combined complexity, we prove that there is a deterministic algorithm for query answering that needs time single exponential in the size of the KB and double exponential in the size of the query, which is optimal. Regarding data complexity, we prove containment in co-NP.

scholarly journals Nominals, Inverses, Counting, and Conjunctive Queries or: Why Infinity is your Friend!

2010 ◽  
Vol 39 ◽  
pp. 429-481 ◽  
Author(s):  
S. Rudolph ◽  
B. Glimm
Keyword(s):  
Knowledge Representation ◽  
Description Logic ◽  
Query Language ◽  
Description Logics ◽  
Knowledge Bases ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Decidability Result ◽  
Wide Range ◽  
Significant Attention

Description Logics are knowledge representation formalisms that provide, for example, the logical underpinning of the W3C OWL standards. Conjunctive queries, the standard query language in databases, have recently gained significant attention as an expressive formalism for querying Description Logic knowledge bases. Several different techniques for deciding conjunctive query entailment are available for a wide range of DLs. Nevertheless, the combination of nominals, inverse roles, and number restrictions in OWL 1 and OWL 2 DL causes unsolvable problems for the techniques hitherto available. We tackle this problem and present a decidability result for entailment of unions of conjunctive queries in the DL ALCHOIQb that contains all three problematic constructors simultaneously. Provided that queries contain only simple roles, our result also shows decidability of entailment of (unions of) conjunctive queries in the logic that underpins OWL 1 DL and we believe that the presented results will pave the way for further progress towards conjunctive query entailment decision procedures for the Description Logics underlying the OWL standards.

scholarly journals Deciding the Loosely Guarded Fragment and Querying Its Horn Fragment Using Resolution

2020 ◽  
Vol 34 (03) ◽  
pp. 3080-3087
Author(s):  
Sen Zheng ◽  
Renate Schmidt
Keyword(s):  
Decision Procedure ◽  
Query Answering ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Guarded Fragment ◽  
Horn Fragment

We consider the following query answering problem: Given a Boolean conjunctive query and a theory in the Horn loosely guarded fragment, the aim is to determine whether the query is entailed by the theory. In this paper, we present a resolution decision procedure for the loosely guarded fragment, and use such a procedure to answer Boolean conjunctive queries against the Horn loosely guarded fragment. The Horn loosely guarded fragment subsumes classes of rules that are prevalent in ontology-based query answering, such as Horn ALCHOI and guarded existential rules. Additionally, we identify star queries and cloud queries, which using our procedure, can be answered against the loosely guarded fragment.

scholarly journals Efficient Private Conjunctive Query Protocol Over Encrypted Data

Cryptography ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 2
Author(s):  
Tushar Kanti Saha ◽  
Takeshi Koshiba
Keyword(s):  
Homomorphic Encryption ◽  
Data Access ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Private Data ◽  
Binary Format ◽  
Main Technique ◽  
Batch Technique ◽  
Outsourced Database ◽  
Packing Method

Conjunctive queries play a key role in retrieving data from a database. In a database, a query containing many conditions in its predicate, connected by an “and/&/∧” operator, is called a conjunctive query. Retrieving the outcome of a conjunctive query from thousands of records is a heavy computational task. Private data access to an outsourced database is required to keep the database secure from adversaries; thus, private conjunctive queries (PCQs) are indispensable. Cheon, Kim, and Kim (CKK) proposed a PCQ protocol using search-and-compute circuits in which they used somewhat homomorphic encryption (SwHE) for their protocol security. As their protocol is far from being able to be used practically, we propose a practical batch private conjunctive query (BPCQ) protocol by applying a batch technique for processing conjunctive queries over an outsourced database, in which both database and queries are encoded in binary format. As a main technique in our protocol, we develop a new data-packing method to pack many data into a single polynomial with the batch technique. We further enhance the performances of the binary-encoded BPCQ protocol by replacing the binary encoding with N-ary encoding. Finally, we compare the performance to assess the results obtained by the binary-encoded BPCQ protocol and the N-ary-encoded BPCQ protocol.

An Improved Set-based Reasoner for the Description Logic 𝒟ℒD4,׆

2021 ◽  
Vol 178 (4) ◽  
pp. 315-346
Author(s):  
Domenico Cantone ◽  
Marianna Nicolosi-Asmundo ◽  
Daniele Francesco Santamaria
Keyword(s):  
Semantic Web ◽  
Set Theory ◽  
Description Logic ◽  
Knowledge Bases ◽  
Query Answering ◽  
Conjunctive Query ◽  
Classification Problems ◽  
Previous Version ◽  
Decidable Fragment ◽  
Stratified Set

We present a KE-tableau-based implementation of a reasoner for a decidable fragment of (stratified) set theory expressing the description logic 𝒟ℒ〈4LQSR,×〉(D) (𝒟ℒD4,×, for short). Our application solves the main TBox and ABox reasoning problems for 𝒟ℒD4,×. In particular, it solves the consistency and the classification problems for 𝒟ℒD4,×-knowledge bases represented in set-theoretic terms, and a generalization of the Conjunctive Query Answering problem in which conjunctive queries with variables of three sorts are admitted. The reasoner, which extends and improves a previous version, is implemented in C++. It supports 𝒟ℒD4,×-knowledge bases serialized in the OWL/XML format and it admits also rules expressed in SWRL (Semantic Web Rule Language).

scholarly journals Exploiting conjunctive queries in description logic programs

2008 ◽  
Vol 53 (1-4) ◽  
pp. 115-152 ◽  
Author(s):  
Thomas Eiter ◽  
Giovambattista Ianni ◽  
Thomas Krennwallner ◽  
Roman Schindlauer
Keyword(s):  
Description Logic ◽  
Logic Programs ◽  
Conjunctive Queries

scholarly journals Learning Description Logic Concepts: When can Positive and Negative Examples be Separated?

2019 ◽  
Author(s):  
Maurice Funk ◽  
Jean Christoph Jung ◽  
Carsten Lutz ◽  
Hadrien Pulcini ◽  
Frank Wolter
Keyword(s):  
Decision Problem ◽  
Description Logic ◽  
Fundamental Question ◽  
Polynomial Hierarchy ◽  
Data Complexity ◽  
Conjunctive Queries ◽  
Complexity Results ◽  
Significant Attention

Learning description logic (DL) concepts from positive and negative examples given in the form of labeled data items in a KB has received significant attention in the literature. We study the fundamental question of when a separating DL concept exists and provide useful model-theoretic characterizations as well as complexity results for the associated decision problem. For expressive DLs such as ALC and ALCQI, our characterizations show a surprising link to the evaluation of ontology-mediated conjunctive queries. We exploit this to determine the combined complexity (between ExpTime and NExpTime) and data complexity (second level of the polynomial hierarchy) of separability. For the Horn DL EL, separability is ExpTime-complete both in combined and in data complexity while for its modest extension ELI it is even undecidable. Separability is also undecidable when the KB is formulated in ALC and the separating concept is required to be in EL or ELI.

scholarly journals The Logical Difference for the Lightweight Description Logic EL

2012 ◽  
Vol 44 ◽  
pp. 633-708 ◽  
Author(s):  
B. Konev ◽  
M. Ludwig ◽  
D. Walther ◽  
F. Wolter
Keyword(s):  
Polynomial Time ◽  
Description Logic ◽  
Snomed Ct ◽  
Conjunctive Queries ◽  
Polynomial Time Algorithms ◽  
The Difference

We study a logic-based approach to versioning of ontologies. Under this view, ontologies provide answers to queries about some vocabulary of interest. The difference between two versions of an ontology is given by the set of queries that receive different answers. We investigate this approach for terminologies given in the description logic EL extended with role inclusions and domain and range restrictions for three distinct types of queries: subsumption, instance, and conjunctive queries. In all three cases, we present polynomial-time algorithms that decide whether two terminologies give the same answers to queries over a given vocabulary and compute a succinct representation of the difference if it is non- empty. We present an implementation, CEX2, of the developed algorithms for subsumption and instance queries and apply it to distinct versions of Snomed CT and the NCI ontology.

scholarly journals Revisiting Controlled Query Evaluation in Description Logics

2019 ◽  
Author(s):  
Domenico Lembo ◽  
Riccardo Rosati ◽  
Domenico Fabio Savo
Keyword(s):  
Private Information ◽  
Description Logics ◽  
Study Data ◽  
Query Answering ◽  
Query Evaluation ◽  
Data Complexity ◽  
Complexity Results ◽  
Controlled Query Evaluation ◽  
Consistent Query Answering ◽  
The Relationship

Controlled Query Evaluation (CQE) is a confidentiality-preserving framework in which private information is protected through a policy, and a (optimal) censor guarantees that answers to queries are maximized without violating the policy. CQE has been recently studied in the context of ontologies, where the focus has been mainly on the problem of the existence of an optimal censor. In this paper we instead consider query answering over all possible optimal censors. We study data complexity of this problem for ontologies specified in the Description Logics DL-LiteR and EL_bottom and for variants of the censor language, which is the language used by the censor to enforce the policy. In our investigation we also analyze the relationship between CQE and the problem of Consistent Query Answering (CQA). Some of the complexity results we provide are indeed obtained through mutual reduction between CQE and CQA.

scholarly journals Natural variations of MeMYB2 in cassava varieties covering a wide range of the reactive oxygen scavenging enzymes under drought

2019 ◽  
Author(s):  
Bin Wang ◽  
Xin Guo ◽  
Shuxia Li ◽  
Jiaxin Liang ◽  
Wenbin Liao ◽  
...  
Keyword(s):  
Antioxidant Enzymes ◽  
Natural Variation ◽  
Reactive Oxygen ◽  
Coding Region ◽  
Oxygen Scavenging ◽  
Natural Variations ◽  
Key Genes ◽  
Scavenging Enzymes ◽  
The Relationship ◽  
Cassava Varieties

Abstract Background Cassava (Manihot esculenta Crantz) is an important tropical crop with excellent stress tolerance and stress resistance genes. The antioxidant enzymes play an important role in regulating the cassava plants respond to stress. To date, little is known the relationship between natural variations of MYB genes that have been proven to regulate stress tolerance in model plants and the diversity of reactive oxygen scavenging enzymes under drought in cassava varieties. Therefore, we conducted this study to discover natural variations in MYB2 gene in association with the reactive oxygen scavenging enzymes.Results Here, the relationship between the natural variation of MYB2 gene and the reactive oxygen scavenging enzymes under drought in cassava were analyzed. Natural variation of antioxidant enzymes in leaf and roots of 97 cassava varieties under drought analyses indicated that the variation of the various antioxidant enzymes is very different among the cassava varieties. MeMYB2 expression profiling analysis indicated that MeMYB2 was up-regulated obviously when induced by drought stress. Re-sequencing analysis of the 97 cassava varieties indicated that the MeMYB2 gene region included 87 single nucleotide variants (SNPs) and two insertion/deletion variants (Insert/ Deletion, Indel), the SNP locus of the coding region of MeMYB2 gene can be divided into 29 haplotypes, including 7 major haplotypes. These 7 major haplotypes can be classified into two categories, one of which is more closely related to wild cassava genotype W14, which indicates that MeMYB2 is positively selected during cassava breeding. Correlation analysis between MeMYB2 and drought tolerance showed that 12 functional SNPs in the MeMYB2 coding region were significantly associated with CAT activity, proline content, SOD activity and other traits, and the prediction of interaction with key genes of drought tolerance was further confirmed that MeMYB2 and key genes involved in CAT, proline and SOD can interact through intermediate metabolic pathways.Conclusions Some natural variations exist in the MeMYB2, which might be involved in regulating the reactive oxygen scavenging enzymes (SOD and CAT) changes under stress. This study will facilitate the understanding of the roles of MYBs in regulating the reactive oxygen scavenging enzymes.

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