Axel Polleres

KR Conference 2021 Conference Paper

Reasoning about Explanations for Non-validation in SHACL

• Shqiponja Ahmetaj
• Robert David
• Magdalena Ortiz
• Axel Polleres
• Bojken Shehu
• Mantas Šimkus

The Shapes Constraint Language (SHACL) is a recently standardized language for describing and validating constraints over RDF graphs. The SHACL specification describes the so-called validation reports, which are meant to explain to the users the outcome of validating an RDF graph against a collection of constraints. Specifically, explaining the reasons why the input graph does not satisfy the constraints is challenging. In fact, the current SHACL standard leaves it open on how such explanations can be provided to the users. In this paper, inspired by works on logic-based abduction and database repairs, we study the problem of explaining non-validation of SHACL constraints. In particular, in our framework non-validation is explained using the notion of a repair, i. e. , a collection of additions and deletions whose application on an input graph results in a repaired graph that does satisfy the given SHACL constraints. We define a collection of decision problems for reasoning about explanations, possibly restricting to explanations that are minimal with respect to cardinality or set inclusion. We provide a detailed characterization of the computational complexity of those reasoning tasks, including the combined and the data complexity.

AILAW Journal 2021 Journal Article

The linked legal data landscape: linking legal data across different countries

• Erwin Filtz
• Sabrina Kirrane
• Axel Polleres

Abstract The European Union is working towards harmonizing legislation across Europe, in order to improve cross-border interchange of legal information. This goal is supported for instance via standards such as the European Law Identifier (ELI) and the European Case Law Identifier (ECLI), which provide technical specifications for Web identifiers and suggestions for vocabularies to be used to describe metadata pertaining to legal documents in a machine readable format. Notably, these ECLI and ELI metadata standards adhere to the RDF data format which forms the basis of Linked Data, and therefore have the potential to form a basis for a pan-European legal Knowledge Graph. Unfortunately, to date said specifications have only been partially adopted by EU member states. In this paper we describe a methodology to transform the existing legal information system used in Austria to such a legal knowledge graph covering different steps from modeling national specific aspects, to population, and finally the integration of legal data from other countries through linked data. We demonstrate the usefulness of this approach by exemplifying practical use cases from legal information search, which are not possible in an automated fashion so far.

KER Journal 2019 Journal Article

TempCourt: evaluation of temporal taggers on a new corpus of court decisions

• María Navas-Loro
• Erwin Filtz
• Víctor Rodríguez-Doncel
• Axel Polleres
• Sabrina Kirrane

Abstract The extraction and processing of temporal expressions (TEs) in textual documents have been extensively studied in several domains; however, for the legal domain it remains an open challenge. This is possibly due to the scarcity of corpora in the domain and the particularities found in legal documents that are highlighted in this paper. Considering the pivotal role played by temporal information when it comes to analyzing legal cases, this paper presents TempCourt, a corpus of 30 legal documents from the European Court of Human Rights, the European Court of Justice, and the United States Supreme Court with manually annotated TEs. The corpus contains two different temporal annotation sets that adhere to the TimeML standard, the first one capturing all TEs and the second dedicated to TEs that are relevant for the case under judgment (thus excluding dates of previous court decisions). The proposed gold standards are subsequently used to compare ten state-of-the-art cross-domain temporal taggers, and to identify not only the limitations of cross-domain temporal taggers but also limitations of the TimeML standard when applied to legal documents. Finally, the paper identifies the need for dedicated resources and the adaptation of existing tools, and specific annotation guidelines that can be adapted to different types of legal documents.

KER Journal 2012 Journal Article

Norms, organizations, and semantics

• Olivier Boissier
• Marco Colombetti
• Michael Luck
• John-Jules Meyer
• Axel Polleres

Abstract This paper integrates the responses to a set of questions from a distinguished set of panelists involved in a discussion at the Agreement Technologies workshop in Cyprus in December 2009. The panel was concerned with the relationship between the research areas of semantics, norms, and organizations, and the ways in which each may contribute to the development of the others in support of next generation agreement technologies.

AAAI Conference 2010 Conference Paper

A General Framework for Representing and Reasoning with Annotated Semantic Web Data

• Umberto Straccia
• Nuno Lopes
• Gergely Lukacsy
• Axel Polleres

We describe a generic framework for representing and reasoning with annotated Semantic Web data, formalise the annotated language, the corresponding deductive system, and address the query answering problem. We extend previous contributions on RDF annotations by providing a unified reasoning formalism and allowing the seamless combination of different annotation domains. We demonstrate the feasibility of our method by instantiating it on (i) temporal RDF; (ii) fuzzy RDF; (iii) and their combination. A prototype shows that implementing and combining new domains is easy and that RDF stores can easily be extended to our framework.

IS Journal 2008 Journal Article

Making Ontologies Talk: Knowledge Interoperability in the Semantic Web

• Monika Lanzenberger
• Jennifer Sampson
• Horst Kargl
• Manuel Wimmer
• Colm Conroy
• Declan O'Sullivan
• David Lewis
• Rob Brennan

Ontologies offer shared vocabularies that are key to agent cooperation and knowledge systems integration as well as fundamental to the Semantic Web. As the number of ontologies increases, so does the need for new tools and techniques to establish agreement between different knowledge representatuions. Six essays based on papers accepted for the First Workshop on Ontology Alignment and Visualization (OnAV 2008) exemplify some of the ways researchers are extending the state of the art in algorithms that can establish correspondences between different but related onologies.

IJCAI Conference 2007 Conference Paper

• Jos de Bruijn
• Thomas Eiter
• Axel Polleres
• Hans Tompits$

In the context of the Semantic Web, several approaches to the combination of ontologies, given in terms of theories of classical first-order logic, and rule bases have been proposed. They either cast rules into classical logic or limit the interaction between rules and ontologies. Autoepistemic logic (AEL) is an attractive formalism which allows to overcome these limitations, by serving as a uniform host language to embed ontologies and nonmonotonic logic programs into it. For the latter, so far only the propositional setting has been considered. In this paper, we present several embeddings of normal and disjunctive non-ground logic programs under the stable-model semantics into first-order AEL, and compare them in combination with classical theories, with respect to stable expansions and autoepistemic consequences. Our results reveal differences and correspondences of the embeddings and provide a useful guidance in the choice of a particular embedding for knowledge combination.

AIJ Journal 2003 Journal Article

A logic programming approach to knowledge-state planning, II: The system

• Thomas Eiter
• Wolfgang Faber
• Nicola Leone
• Gerald Pfeifer
• Axel Polleres

In Part I of this series of papers, we have proposed a new logic-based planning language, called K. This language facilitates the description of transitions between states of knowledge and it is well suited for planning under incomplete knowledge. Nonetheless, K also supports the representation of transitions between states of the world (i. e. , states of complete knowledge) as a special case, proving to be very flexible. In the present Part II, we describe the DLV K planning system, which implements K on top of the disjunctive logic programming system DLV. This novel planning system allows for solving hard planning problems, including secure planning under incomplete initial states (often called conformant planning in the literature), which cannot be solved at all by other logic-based planning systems such as traditional satisfiability planners. We present a detailed comparison of the DLV K system to several state-of-the-art conformant planning systems, both at the level of system features and on benchmark problems. Our results indicate that, thanks to the power of knowledge-state problem encoding, the DLV K system is competitive even with special purpose conformant planning systems, and it often supplies a more natural and simple representation of the planning problems.

JELIA Conference 2002 Conference Paper

Answer Set Planning under Action Costs

• Thomas Eiter
• Wolfgang Faber 0001
• Nicola Leone
• Gerald Pfeifer
• Axel Polleres

Abstract We present \( \mathcal{K}^c \), which extends the declarative planning language \( \mathcal{K} \) by action costs and optimal plans that minimize overall action costs (cheapest plans). As shown, this novel language allows for expressing some nontrivial planning tasks in an elegant way. Furthermore, it flexibly allows for representing planning problems under other optimality criteria as well, such as computing “fastest” plans (with the least number of steps), and refinement combinations of cheap and fast plans. Our experience is encouraging and supports the claim that answer set planning may be a valuable approach to advanced planning systems in which intricate planning tasks can be naturally specified and effectively solved.

JELIA Conference 2002 Conference Paper

The DLV K Planning System: Progress Report

• Thomas Eiter
• Wolfgang Faber 0001
• Nicola Leone
• Gerald Pfeifer
• Axel Polleres

Abstract The knowledge based planning system DLV K implements answer set planning on top of the DLV system [ 1 ]. It is developed at TU Wien and supports the declarative language K [ 2 ], [ 3 ] and its extension K c [ 5 ]. The language K is syntactically similar to the action language C [ 7 ], but semantically closer to answer set programming (by including default negation, for example). K and K c offer the following distinguishing features:

JELIA Conference 2002 Conference Paper

The DLV System

• Nicola Leone
• Gerald Pfeifer
• Wolfgang Faber 0001
• Francesco Calimeri
• Tina Dell'Armi
• Thomas Eiter
• Georg Gottlob
• Giovambattista Ianni

Abstract The development of the DLV system has started as a research projectfinanced by FWF (the Austrian Science Funds) in 1996, and has evolved into an international collaboration over the years. Currently, the University of Calabria and TU Wien participate in the project, supported by a scientific-technological collaboration between Italy and Austria. At the time of writing, the latest version of the system has been released on April 12, 2002.