172 research outputs found
Do Repeat Yourself: Understanding Sufficient Conditions for Restricted Chase Non-Termination
The disjunctive restricted chase is a sound and complete procedure for
solving boolean conjunctive query entailment over knowledge bases of
disjunctive existential rules. Alas, this procedure does not always terminate
and checking if it does is undecidable. However, we can use acyclicity notions
(sufficient conditions that imply termination) to effectively apply the chase
in many real-world cases. To know if these conditions are as general as
possible, we can use cyclicity notions (sufficient conditions that imply
non-termination). In this paper, we discuss some issues with previously
existing cyclicity notions, propose some novel notions for non-termination by
dismantling the original idea, and empirically verify the generality of the new
criteria
Query Rewriting with Disjunctive Existential Rules and Mappings
We consider the issue of answering unions of conjunctive queries (UCQs) with
disjunctive existential rules and mappings. While this issue has already been
well studied from a chase perspective, query rewriting within UCQs has hardly
been addressed yet. We first propose a sound and complete query rewriting
operator, which has the advantage of establishing a tight relationship between
a chase step and a rewriting step. The associated breadth-first query rewriting
algorithm outputs a minimal UCQ-rewriting when one exists. Second, we show that
for any ``truly disjunctive'' nonrecursive rule, there exists a conjunctive
query that has no UCQ-rewriting. It follows that the notion of finite
unification sets (fus), which denotes sets of existential rules such that any
UCQ admits a UCQ-rewriting, seems to have little relevance in this setting.
Finally, turning our attention to mappings, we show that the problem of
determining whether a UCQ admits a UCQ-rewriting through a disjunctive mapping
is undecidable. We conclude with a number of open problems.Comment: This report contains the paper accepted at KR 2023 and an appendix
with full proofs. 24 page
LIPIcs, Volume 261, ICALP 2023, Complete Volume
LIPIcs, Volume 261, ICALP 2023, Complete Volum
Unsettled Urban Space: Routines, Temporalities and Contestations
While urban life can be characterized by endeavors to settle stable and safe environments, for many people, urban space is rarely stable or safe; it is uncertain, troubled, imbued with challenges and perpetually under pressure. As the concept of unsettled appears to define the contemporary urban experience, this multidisciplinary book investigates the conflicts and possibilities of settling and unsettling through open and speculative analysis.
The analytical prism of unsettled renders urban space an indeterminate ground unfolding through routines, temporalities and contestations in constant tension between settling and unsettling. Such contrasting experiences are contingent on how urban societies confront, undergo and overcome turbulence and difficulties in time and space. Contributions drawing on theoretical reflections and empirical accounts—from Argentina, Austria, Germany, Greece, Italy, the Netherlands, the UAE, the UK, the USA and Vietnam—give insights into plural occurrences of the unsettled, which might tie down or unleash transformative, liberatory and emancipatory potentials.
This book is for students, professionals and researchers interested in the uncertainties, foundations, disturbances, inconsistencies, residuals and blind fields, which constitute the urban both as lived space and as social, cultural and political ideal
Saturation-based Boolean conjunctive query answering and rewriting for the guarded quantification fragments
Query answering is an important problem in AI, database and knowledge
representation. In this paper, we develop saturation-based Boolean conjunctive
query answering and rewriting procedures for the guarded, the loosely guarded
and the clique-guarded fragments. Our query answering procedure improves
existing resolution-based decision procedures for the guarded and the loosely
guarded fragments and this procedure solves Boolean conjunctive query answering
problems for the guarded, the loosely guarded and the clique-guarded fragments.
Based on this query answering procedure, we also introduce a novel
saturation-based query rewriting procedure for these guarded fragments. Unlike
mainstream query answering and rewriting methods, our procedures derive a
compact and reusable saturation, namely a closure of formulas, to handle the
challenge of querying for distributed datasets. This paper lays the theoretical
foundations for the first automated deduction decision procedures for Boolean
conjunctive query answering and the first saturation-based Boolean conjunctive
query rewriting in the guarded, the loosely guarded and the clique-guarded
fragments
Finite Herbrand Models for Restricted First-Order Clauses
We call a Herbrand model of a set of first-order clauses finite, if each of the predicates in the clauses is interpreted by a finite set of ground terms. We consider first-order clauses with the signature restricted to unary predicate and function symbols and one variable. Deciding the existence of a finite Herbrand model for a set of such clauses is known to be ExpTime-hard even when clauses are restricted to an anti-Horn form. Here we present an ExpTime algorithm to decide if a finite Herbrand model exists in the more general case of arbitrary clauses. Moreover, we describe a way to generate finite Herbrand models, if they exist. Since there can be infinitely many minimal finite Herbrand models, we propose a new notion of acyclic Herbrand models. If there is a finite Herbrand model for a set of restricted clauses, then there are finitely many (at most triple-exponentially many) acyclic Herbrand models. We show how to generate all of them
The Afterlife of the Shoah in Central and Eastern European Cultures
The Afterlife of the Shoah in Central and Eastern European Cultures is a collection of essays by literary scholars from Germany, the US, and Central Eastern Europe offering insight into the specific ways of representing the Shoah and its aftereffects as well as its entanglement with other catastrophic events in the region. Introducing the conceptual frame of postcatastrophe, the collected essays explore the discursive and artistic space the Shoah occupies in the countries between Moscow and Berlin. Postcatastrophe is informed by the knowledge of other concepts of "post" and shares their insight into forms of transmission and latency; in contrast to them, explores the after-effects of extreme events on a collective, aesthetic, and political rather than a personal level. The articles use the concept of postcatastrophe as a key to understanding the entangled and conflicted cultures of remembrance in postsocialist literatures and the arts dealing with events, phenomena, and developments that refuse to remain in the past and still continue to shape perceptions of today’s societies in Eastern Europe. As a contribution to memory studies as well as to literary criticism with a special focus on Shoah remembrance after socialism, this book is of great interest to students and scholars of European history, and those interested in historical memory more broadly
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