503 research outputs found
A novel characterization of the complexity class based on counting and comparison
This is the author's accepted versionFinal version available from Elsevier via the DOI in this recordThe complexity class Ī2P, which is the class of languages recognizable by deterministic Turing machines in polynomial time with at most logarithmic many calls to an NP oracle, received extensive attention in the literature. Its complete problems can be characterized by different specific tasks, such as deciding whether the optimum solution of an NP problem is unique, or whether it is in some sense āoddā (e.g., whether its size is an odd number). In this paper, we introduce a new characterization of this class and its generalization ĪkP to the k-th level of the polynomial hierarchy. We show that problems in ĪkP are also those whose solution involves deciding, for two given sets A and B of instances of two Ī£kā1P-complete (or Ī kā1P-complete) problems, whether the number of āyesā-instances in A is greater than those in B. Moreover, based on this new characterization, we provide a novel sufficient condition for ĪkP-hardness. We also define the general problem Comp-Validk, which is proven here Īk+1P-complete. Comp-Validk is the problem of deciding, given two sets A and B of quantified Boolean formulas with at most k alternating quantifiers, whether the number of valid formulas in A is greater than those in B. Notably, the problem Comp-Sat of deciding whether a set contains more satisfiable Boolean formulas than another set, which is a particular case of Comp-Valid1, demonstrates itself as a very intuitive Ī2P-complete problem. Nonetheless, to our knowledge, it eluded its formal definition to date. In fact, given its strict adherence to the count-and-compare semantics here introduced, Comp-Validk is among the most suitable tools to prove ĪkP-hardness of problems involving the counting and comparison of the number of āyesā-instances in two sets. We support this by showing that the Ī2P-hardness of the Max voting scheme over mCP-nets is easily obtained via the new characterization of ĪkP introduced in this paper.This work was supported by the UK EPSRC grants EP/J008346/1, EP/L012138/1, and EP/M025268/1, and by The Alan Turing Institute under the EPSRC grant EP/N510129/1. We thank Dominik Peters and the anonymous reviewers for their helpful comments on a preliminary version of the paper
Complexity of Approximate Query Answering under Inconsistency in Datalog+/-
This is the author accepted manuscript. The final version is freely available from IJCAI via the link in this recordSeveral semantics have been proposed to query inconsistent
ontological knowledge bases, including
the intersection of repairs and the intersection of
closed repairs as two approximate inconsistencytolerant
semantics. In this paper, we analyze the
complexity of conjunctive query answering under
these two semantics for a wide range of DatalogĀ±
languages. We consider both the standard setting,
where errors may only be in the database, and the
generalized setting, where also the rules of a DatalogĀ±
knowledge base may be erroneous.This work was supported by The Alan Turing Institute under
the UK EPSRC grant EP/N510129/1, and by the EPSRC
grants EP/R013667/1, EP/L012138/1, and EP/M025268/1
Complexity of Inconsistency-Tolerant Query Answering in Datalog+/- under Cardinality-Based Repairs
This is the author accepted manuscript. The final version is available from Association for the Advancement of Artificial Intelligence (AAAI) via the link in this recordQuerying inconsistent ontological knowledge bases is an important
problem in practice, for which several inconsistencytolerant
query answering semantics have been proposed, including
query answering relative to all repairs, relative to
the intersection of repairs, and relative to the intersection of
closed repairs. In these semantics, one assumes that the input
database is erroneous, and the notion of repair describes a
maximally consistent subset of the input database, where different
notions of maximality (such as subset and cardinality
maximality) are considered. In this paper, we give a precise
picture of the computational complexity of inconsistencytolerant
(Boolean conjunctive) query answering in a wide
range of DatalogĀ± languages under the cardinality-based versions
of the above three repair semantics.This work was supported by the Alan
Turing Institute under the UK EPSRC grant EP/N510129/1,
and by the EPSRC grants EP/R013667/1, EP/L012138/1,
and EP/M025268/1
Complexity of Approximate Query Answering under Inconsistency in Datalog+/-
This is the author accepted manuscript. The final version is available from the publisher via the link in this recordSeveral semantics have been proposed to query inconsistent ontological
knowledge bases, including the intersection of repairs and the intersection of closed
repairs as two approximate inconsistency-tolerant semantics. In this paper, we
analyze the complexity of conjunctive query answering under these two semantics
for a wide range of DatalogĀ± languages. We consider both the standard setting,
where errors may only be in the database, and the generalized setting, where also
the rules of a DatalogĀ± knowledge base may be erroneous.This work was supported by The Alan Turing Institute under the
UK EPSRC grant EP/N510129/1, and by the EPSRC grants EP/R013667/1, EP/L012138/1,
and EP/M025268/1
Few-Shot Out-of-Domain Transfer Learning of Natural Language Explanations in a Label-Abundant Setup
Training a model to provide natural language explanations (NLEs) for its predictions usually requires the acquisition of task-specific NLEs, which is time- and resource-consuming. A potential solution is the few-shot out-of-domain transfer of NLEs from a parent task with many NLEs to a child task. In this work, we examine the setup in which the child task has few NLEs but abundant labels. We establish four few-shot transfer learning methods that cover the possible fine-tuning combinations of the labels and NLEs for the parent and child tasks. We transfer explainability from a large natural language inference dataset (e-SNLI) separately to two child tasks: (1) hard cases of pronoun resolution, where we introduce the small-e-WinoGrande dataset of NLEs on top of the WinoGrande dataset, and (2) commonsense validation (ComVE). Our results demonstrate that the parent task helps with NLE generation and we establish the best methods for this setup
Twenty Years of Student Scholarship: Celebrating the Dalhousie Journal of Legal Studies
In this paper, we propose a novel controllable text-to-image generative
adversarial network (ControlGAN), which can effectively synthesise high-quality
images and also control parts of the image generation according to natural
language descriptions. To achieve this, we introduce a word-level spatial and
channel-wise attention-driven generator that can disentangle different visual
attributes, and allow the model to focus on generating and manipulating
subregions corresponding to the most relevant words. Also, a word-level
discriminator is proposed to provide fine-grained supervisory feedback by
correlating words with image regions, facilitating training an effective
generator which is able to manipulate specific visual attributes without
affecting the generation of other content. Furthermore, perceptual loss is
adopted to reduce the randomness involved in the image generation, and to
encourage the generator to manipulate specific attributes required in the
modified text. Extensive experiments on benchmark datasets demonstrate that our
method outperforms existing state of the art, and is able to effectively
manipulate synthetic images using natural language descriptions. Code is
available at https://github.com/mrlibw/ControlGAN.Comment: NeurIPS 201
Query Answer Explanations under Existential Rules
Ontology-mediated query answering is an extensively studied paradigm, which aims at improving
query answers with the use of a logical theory. In this paper, we focus on ontology languages based on
existential rules, and we carry out a thorough complexity analysis of the problem of explaining query
answers in terms of minimal subsets of database facts and related task
1994 Annual Report Town of Middleton, Massachusetts Two Hundred and Sixty-Sixth Municipal Year
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Aggregating preferences over combinatorial domains has many applications in artificial intelligence (AI). Given the
inherent exponential nature of preferences over combinatorial domains, compact representation languages are needed
to represent them, and (m)CP-nets are among the most studied ones. Sequential and global voting are two different
ways of aggregating preferences represented via CP-nets. In sequential voting, agentsā preferences are aggregated
feature-by-feature. For this reason, sequential voting may exhibit voting paradoxes, i.e., the possibility to select
sub-optimal outcomes when preferences have specific feature dependencies. To avoid paradoxes in sequential voting,
one has often assumed the (quite) restrictive constraint of O-legality, which imposes a shared common topological
order among all the agentsā CP-nets. On the contrary, in global voting, CP-nets are considered as a whole during the
preference aggregation process. For this reason, global voting is immune from the voting paradoxes of sequential
voting, and hence there is no need to impose restrictions over the CP-netsā structure when preferences are aggregated
via global voting. Sequential voting over O-legal CP-nets received much attention, and O-legality of CP-nets has
often been required in other studies. On the other hand, global voting over non-O-legal CP-nets has not carefully been
analyzed, despite it was explicitly stated in the literature that a theoretical comparison between global and sequential
voting was highly promising and a precise complexity analysis for global voting has been asked for multiple times.
In quite a few works, only very partial results on the complexity of global voting over CP-nets have been given. In
this paper, we start to fill this gap by carrying out a thorough computational complexity analysis of global voting
tasks, for Pareto and majority voting, over not necessarily O-legal acyclic binary polynomially connected (m)CP-nets.
We show that all these problems belong to various levels of the polynomial hierarchy, and some of them are even in
P or LOGSPACE. Our results are a notable achievement, given that the previously known upper bound for most of
these problems was the complexity class EXPTIME. We provide various exact complexity results showing tight lower
bounds and matching upper bounds for problems that (up to now) did not have any explicit non-obvious lower bound.Engineering and Physical Sciences Research Council (EPSRC
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