scholarly journals Sticky Existential Rules and Disjunction are Incompatible

2021 ◽  
Author(s):  
Michael Morak
Keyword(s):  
Query Answering ◽  
Fixed Set ◽  
Existential Quantification ◽  
Undecidability Result

Stickiness is one of the well-known properties in the literature that guarantees decidability of query answering under sets of existential rules, that is, Datalog rules extended with existential quantification in rule heads. In this note, we investigate whether this remains true in the case when rule heads are allowed to be disjunctive. We answer this question in the negative, providing a strong undecidability result that shows that the concept of stickiness cannot be extended to disjunctive existential rules, even when considering only fixed atomic queries and a fixed set of rules. This provides evidence that, in order to keep query answering decidable, a stronger property than stickiness is needed in the disjunctive case.

scholarly journals PAGOdA: Pay-As-You-Go Ontology Query Answering Using a Datalog Reasoner

2015 ◽  
Vol 54 ◽  
pp. 309-367 ◽  
Author(s):  
Yujiao Zhou ◽  
Bernardo Cuenca Grau ◽  
Yavor Nenov ◽  
Mark Kaminski ◽  
Ian Horrocks
Keyword(s):  
Hybrid Approach ◽  
Expressive Power ◽  
Query Answering ◽  
Reasoning Task ◽  
First Order ◽  
Ontology Language ◽  
Extensive Evaluation ◽  
Black Boxes ◽  
Wide Range ◽  
Existential Quantification

Answering conjunctive queries over ontology-enriched datasets is a core reasoning task for many applications. Query answering is, however, computationally very expensive, which has led to the development of query answering procedures that sacrifice either expressive power of the ontology language, or the completeness of query answers in order to improve scalability. In this paper, we describe a hybrid approach to query answering over OWL 2 ontologies that combines a datalog reasoner with a fully-fledged OWL 2 reasoner in order to provide scalable `pay-as-you-go' performance. The key feature of our approach is that it delegates the bulk of the computation to the datalog reasoner and resorts to expensive OWL 2 reasoning only as necessary to fully answer the query. Furthermore, although our main goal is to efficiently answer queries over OWL 2 ontologies and data, our technical results are very general and our approach is applicable to first-order knowledge representation languages that can be captured by rules allowing for existential quantification and disjunction in the head; our only assumption is the availability of a datalog reasoner and a fully-fledged reasoner for the language of interest, both of which are used as `black boxes'. We have implemented our techniques in the PAGOdA system, which combines the datalog reasoner RDFox and the OWL 2 reasoner HermiT. Our extensive evaluation shows that PAGOdA succeeds in providing scalable pay-as-you-go query answering for a wide range of OWL 2 ontologies, datasets and queries.

scholarly journals Enhancing Existential Rules by Closed-World Variables

2018 ◽  
Author(s):  
Giovanni Amendola ◽  
Nicola Leone ◽  
Marco Manna ◽  
Pierfrancesco Veltri
Keyword(s):  
Computational Complexity ◽  
Query Answering ◽  
Open World ◽  
Closed World ◽  
Open World Assumption ◽  
Existential Quantification

Existential rules generalize Datalog with existential quantification in the head. Natively, Datalog is interpreted under a closed-world semantics, while existential rules typically employ the open-world assumption. The interpretation domain in the latter case is enlarged by infinitely many "anonymous" individuals. Then, in any rule, each variable ranges over all individuals, even if not needed or required. In this paper, we enhance existential rules by closed-world variables to consciously reason on the properties of "known" (non-anonymous) and arbitrary individuals in different ways. Accordingly, we uniformly generalize the basic classes of existential rules that ensure decidability of ontology-based query answering. For them, after observing that decidability is preserved, we prove that a strict increase in expressiveness is gained, and in most cases the computational complexity is not altered.

Development of a Jacobian Module for Advanced Pulp and Paper Simulation and Control

TAPPI Journal ◽  
2009 ◽  
Vol 8 (1) ◽  
pp. 4-11
Author(s):  
MOHAMED CHBEL ◽  
LUC LAPERRIÈRE
Keyword(s):  
Control System ◽  
Nonlinear Behavior ◽  
Simulation Software ◽  
Pulp And Paper ◽  
Pid Controllers ◽  
Tuning Parameters ◽  
Pid Tuning ◽  
Fixed Set ◽  
And Control ◽  
Operating Points

Pulp and paper processes frequently present nonlinear behavior, which means that process dynam-ics change with the operating points. These nonlinearities can challenge process control. PID controllers are the most popular controllers because they are simple and robust. However, a fixed set of PID tuning parameters is gen-erally not sufficient to optimize control of the process. Problems related to nonlinearities such as sluggish or oscilla-tory response can arise in different operating regions. Gain scheduling is a potential solution. In processes with mul-tiple control objectives, the control strategy must further evaluate loop interactions to decide on the pairing of manipulated and controlled variables that minimize the effect of such interactions and hence, optimize controller’s performance and stability. Using the CADSIM Plus™ commercial simulation software, we developed a Jacobian sim-ulation module that enables automatic bumps on the manipulated variables to calculate process gains at different operating points. These gains can be used in controller tuning. The module also enables the control system designer to evaluate loop interactions in a multivariable control system by calculating the Relative Gain Array (RGA) matrix, of which the Jacobian is an essential part.

Computing Cores for Existential Rules with the Standard Chase and ASP

2020 ◽  
Author(s):  
Markus Krötzsch
Keyword(s):  
Large Class ◽  
Data Exchange ◽  
Answer Set Programming ◽  
Query Answering ◽  
Universal Model ◽  
The Core ◽  
Universal Models ◽  
General Terms ◽  
Special Cases ◽  
The Many

To reason with existential rules (a.k.a. tuple-generating dependencies), one often computes universal models. Among the many such models of different structure and cardinality, the core is arguably the “best”. Especially for finitely satisfiable theories, where the core is the unique smallest universal model, it has advantages in query answering, non-monotonic reasoning, and data exchange. Unfortunately, computing cores is difficult and not supported by most reasoners. We therefore propose ways of computing cores using practically implemented methods from rule reasoning and answer set programming. Our focus is on cases where the standard chase algorithm produces a core. We characterise this desirable situation in general terms that apply to a large class of cores, derive concrete approaches for decidable special cases, and generalise these approaches to non-monotonic extensions of existential rules.

Computer simulation to evaluate the economics of landfill gas recovery

1998 ◽  
Vol 38 (2) ◽  
pp. 201-208
Author(s):  
M. W. Milke
Keyword(s):  
Computer Simulation ◽  
Computer Program ◽  
Landfill Gas ◽  
Base Case ◽  
Simulation Tool ◽  
Hypothetical Case ◽  
Gas Recovery ◽  
Fixed Set ◽  
Key Variables ◽  
Simulation Results

A need exists for tools to improve evaluations of the economics of landfill gas recovery. A computer simulation tool is presented. It uses a spreadsheet computer program to calculate the economics for a fixed set of inputs, and a simulation program to consider variations in the inputs. The method calculates the methane generated each year, and estimates the costs and incomes associated with the recovery and sale of the gas. Base case results are presented for a city of 500,000. An uncertainty analysis for a hypothetical case is presented. The simulation results can help an analyst see the key variables affecting the economics of a project.

METHOD OF COMPARATIVE EVALUATION OF OPTIONS FOR JOINT USE OF TRADITIONAL AND NEW TYPES OF HIGH-TECH PRODUCTS

2019 ◽  
pp. 100-107
Author(s):  
A. M. Batkovsky ◽  
A. V. Leonov ◽  
A. Yu. Pronin ◽  
A. V. Fomina
Keyword(s):  
Comparative Evaluation ◽  
New Products ◽  
Economic Assessment ◽  
The State ◽  
Financial Resources ◽  
High Tech ◽  
Pareto Optimal ◽  
Fixed Set ◽  
The Law

In conditions of limited financial resources of the state, the task of assessing the appropriateness and choosing rational options for the joint use of traditional and new types of high-tech products is topical. The paper proposes a method for substantiating rational options for the joint use of traditional and new products of high-tech products, based on the criteria of their comparative technical and economic assessment, namely, comparing the achieved efficiency and the required cost of performing a fixed set of tasks. The dialectical foundations of the method are presented, in particular, it is established that the law of development of high-tech products fully corresponds to the well-known classical law of «denial of denial». The structure of the method, the order of formation of the set of Pareto-optimal options for the joint use of traditional and new products, as well as the algorithm for choosing a rational option are considered.

Asymptotics with remainder term for moments of the total cycle number of random A-permutation

2021 ◽  
Vol 31 (1) ◽  
pp. 51-60
Author(s):  
Arsen L. Yakymiv
Keyword(s):  
Remainder Term ◽  
Random Permutation ◽  
Natural Numbers ◽  
Cycle Number ◽  
Fixed Set ◽  
Cycle Lengths

Abstract Dedicated to the memory of Alexander Ivanovich Pavlov. We consider the set of n-permutations with cycle lengths belonging to some fixed set A of natural numbers (so-called A-permutations). Let random permutation τ n be uniformly distributed on this set. For some class of sets A we find the asymptotics with remainder term for moments of total cycle number of τ n .

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).

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