203 research outputs found
Notation3 as an Existential Rule Language
Notation3 Logic (\nthree) is an extension of RDF that allows the user to
write rules introducing new blank nodes to RDF graphs. Many applications (e.g.,
ontology mapping) rely on this feature as blank nodes -- used directly or in
auxiliary constructs -- are omnipresent on the Web. However, the number of fast
\nthree reasoners covering this very important feature of the logic is rather
limited. On the other hand, there are engines like VLog or Nemo which do not
directly support Semantic Web rule formats but which are developed and
optimized for very similar constructs: existential rules. In this paper, we
investigate the relation between \nthree rules with blank nodes in their heads
and existential rules. We identify a subset of \nthree which can be mapped
directly to existential rules and define such a mapping preserving the
equivalence of \nthree formulae. In order to also illustrate that in some cases
\nthree reasoning could benefit from our translation, we then employ this
mapping in an implementation to compare the performance of the \nthree
reasoners EYE and cwm to VLog and Nemo on \nthree rules and their mapped
counterparts. Our tests show that the existential rule reasoners perform
particularly well for use cases containing many facts while especially the EYE
reasoner is very fast when dealing with a high number of dependent rules. We
thus provide a tool enabling the Semantic Web community to directly use
existing and future existential rule reasoners and benefit from the findings of
this active community
LIPIcs, Volume 261, ICALP 2023, Complete Volume
LIPIcs, Volume 261, ICALP 2023, Complete Volum
Decidability of Querying First-Order Theories via Countermodels of Finite Width
We propose a generic framework for establishing the decidability of a wide
range of logical entailment problems (briefly called querying), based on the
existence of countermodels that are structurally simple, gauged by certain
types of width measures (with treewidth and cliquewidth as popular examples).
As an important special case of our framework, we identify logics exhibiting
width-finite finitely universal model sets, warranting decidable entailment for
a wide range of homomorphism-closed queries, subsuming a diverse set of
practically relevant query languages. As a particularly powerful width measure,
we propose Blumensath's partitionwidth, which subsumes various other commonly
considered width measures and exhibits highly favorable computational and
structural properties. Focusing on the formalism of existential rules as a
popular showcase, we explain how finite partitionwidth sets of rules subsume
other known abstract decidable classes but -- leveraging existing notions of
stratification -- also cover a wide range of new rulesets. We expose natural
limitations for fitting the class of finite unification sets into our picture
and provide several options for remedy
LIPIcs, Volume 274, ESA 2023, Complete Volume
LIPIcs, Volume 274, ESA 2023, Complete Volum
LIPIcs, Volume 258, SoCG 2023, Complete Volume
LIPIcs, Volume 258, SoCG 2023, Complete Volum
A Framework for Combining Entity Resolution and Query Answering in Knowledge Bases
We propose a new framework for combining entity resolution and query
answering in knowledge bases (KBs) with tuple-generating dependencies (tgds)
and equality-generating dependencies (egds) as rules. We define the semantics
of the KB in terms of special instances that involve equivalence classes of
entities and sets of values. Intuitively, the former collect all entities
denoting the same real-world object, while the latter collect all alternative
values for an attribute. This approach allows us to both resolve entities and
bypass possible inconsistencies in the data. We then design a chase procedure
that is tailored to this new framework and has the feature that it never fails;
moreover, when the chase procedure terminates, it produces a universal
solution, which in turn can be used to obtain the certain answers to
conjunctive queries. We finally discuss challenges arising when the chase does
not terminate
Tools and Algorithms for the Construction and Analysis of Systems
This open access book constitutes the proceedings of the 28th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2022, which was held during April 2-7, 2022, in Munich, Germany, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2022. The 46 full papers and 4 short papers presented in this volume were carefully reviewed and selected from 159 submissions. The proceedings also contain 16 tool papers of the affiliated competition SV-Comp and 1 paper consisting of the competition report. TACAS is a forum for researchers, developers, and users interested in rigorously based tools and algorithms for the construction and analysis of systems. The conference aims to bridge the gaps between different communities with this common interest and to support them in their quest to improve the utility, reliability, exibility, and efficiency of tools and algorithms for building computer-controlled systems
Pushing Optimal ABox Repair from EL Towards More Expressive Horn-DLs
Ontologies based on Description Logic (DL) represent general background knowledge in a terminology (TBox) and the actual data in an ABox. DL systems can then be used to compute consequences (such as answers to certain queries) from an ontology consisting of a TBox and an ABox. Since both human-made and machine-learned data sets may contain errors, which manifest themselves as unintuitive or obviously incorrect consequences, repairing DL-based ontologies in the sense of removing such unwanted consequences is an important topic in DL research. Most of the repair approaches described in the literature produce repairs that are not optimal, in the sense that they do not guarantee that only a minimal set of consequences is removed. In a series of papers, we have developed an approach for computing optimal repairs, starting with the restricted setting of an EL instance store, extending this to the more general setting of a quantified ABox (where some individuals may be anonymous), and then adding a static EL TBox.
Here, we extend the expressivity of the underlying DL considerably, by adding nominals, inverse roles, regular role inclusions and the bottom concept to EL, which yields a fragment of the well-known DL Horn-SROIQ. The ideas underlying our repair approach still apply to this DL, though several non-trivial extensions are needed to deal with the new constructors and axioms. The developed repair approach can also be used to treat unwanted consequences expressed by certain conjunctive queries or regular path queries, and to handle Horn-ALCOI TBoxes with regular role inclusions.This is an extended version of an article accepted at KR 2022
Unique Characterisability and Learnability of Temporal Instance Queries
We aim to determine which temporal instance queries can be uniquely
characterised by a (polynomial-size) set of positive and negative temporal data
examples. We start by considering queries formulated in fragments of
propositional linear temporal logic LTL that correspond to conjunctive queries
(CQs) or extensions thereof induced by the until operator. Not all of these
queries admit polynomial characterisations but by restricting them further to
path-shaped queries we identify natural classes that do. We then investigate
how far the obtained characterisations can be lifted to temporal knowledge
graphs queried by 2D languages combining LTL with concepts in description
logics EL or ELI (i.e., tree-shaped CQs). While temporal operators in the scope
of description logic constructors can destroy polynomial characterisability, we
obtain general transfer results for the case when description logic
constructors are within the scope of temporal operators. Finally, we apply our
characterisations to establish (polynomial) learnability of temporal instance
queries using membership queries in the active learning framework
- …