Publications of Stefan Ellmauthaler


[1] Gerhard Brewka, Stefan Ellmauthaler, Ricardo Gonçalves, Matthias Knorr, João Leite, and Jörg Pührer. Reactive multi-context systems: Heterogeneous reasoning in dynamic environments. Artificial Intelligence, 256:68--104, 2018. [ bib | DOI | http ]
Abstract Managed multi-context systems (mMCSs) allow for the integration of heterogeneous knowledge sources in a modular and very general way. They were, however, mainly designed for static scenarios and are therefore not well-suited for dynamic environments in which continuous reasoning over such heterogeneous knowledge with constantly arriving streams of data is necessary. In this paper, we introduce reactive multi-context systems (rMCSs), a framework for reactive reasoning in the presence of heterogeneous knowledge sources and data streams. We show that rMCSs are indeed well-suited for this purpose by illustrating how several typical problems arising in the context of stream reasoning can be handled using them, by showing how inconsistencies possibly occurring in the integration of multiple knowledge sources can be handled, and by arguing that the potential non-determinism of rMCSs can be avoided if needed using an alternative, more skeptical well-founded semantics instead with beneficial computational properties. We also investigate the computational complexity of various reasoning problems related to rMCSs. Finally, we discuss related work, and show that rMCSs do not only generalize mMCSs to dynamic settings, but also capture/extend relevant approaches w.r.t. dynamics in knowledge representation and stream reasoning.

Keywords: Heterogeneous knowledge, Stream reasoning, Knowledge integration, Reactive systems, Dynamic systems
[2] Stefan Ellmauthaler. Multi-Context Reasoning in Continuous Data-Flow Environments. PhD thesis, Leipzig University, 2018. [ bib | http ]
[3] Gerhard Brewka, Stefan Ellmauthaler, Hannes Strass, Johannes P. Wallner, and Stefan Woltran. Abstract dialectical frameworks. an overview. IfCoLog Journal of Logics and their Applications Volume 4, number 8. Formal Argumentation, 4(8):2263--2317, 10 2017. [ bib | .html ]
This article describes abstract dialectical frameworks, or adfs for short. adfs are generalizations of the widely used Dung argumentation frameworks. Whereas the latter focus on a single relation among abstract arguments, namely attack, adfs allow arbitrary relationships among arguments to be expressed. For instance, arguments may support each other, or a group of arguments may jointly attack another one while each single member of the group is not strong enough to do so. This additional expressiveness is achieved by handling acceptance conditions for each argument explicitly.

The semantics of adfs are inspired by approximation fixpoint theory (AFT), a general algebraic theory for approximation based semantics developed by Denecker, Marek and Truszczyski. We briefly introduce AFT and discuss its role in argumentation. This puts us in a position to formally introduce adfs and their semantics. In particular, we show how the most important Dung semantics can be generalized to adfs. Furthermore, we illustrate the use of adfs as semantical tool in various modelling scenarios, demonstrating how typical representations in argumentation can be equipped with precise semantics via translations to adfs. We also present grappa, a related approach where the semantics of arbitrary labelled argument graphs can be directly defined in an adf-like manner, circumventing the need for explicit translations. Finally, we address various computational aspects of adfs, like complexity, expressiveness and realizability, and present several implemented systems.

[4] Hannes Strass and Stefan Ellmauthaler. goDIAMOND 0.6.6 -- ICCMA 2017 system description, 2017. Second International Competition on Computational Models of Argumentation: http://www.dbai.tuwien.ac.at/iccma17/. [ bib | http ]
[5] Stefan Ellmauthaler and Hannes Strass. DIAMOND 3.0 - A native C++ implementation of DIAMOND. In 6th International Conference on Computational Models of Argument (COMMA 2016), Potsdam, Germany, 12-16 September, 2016., volume 287 of Frontiers in Artificial Intelligence and Applications, pages 471--472. IOS Press, 2016. [ bib | DOI | http ]
We present a reimplementation of the DIAMOND system for computing with abstract dialectical frameworks. The original DIAMOND was a script-based tool that called an external ASP solver. This reimplementation uses the clingo library in a native C++ environment and thus avoids communication overhead.

[6] Gerhard Brewka, Stefan Ellmauthaler, Ricardo Gonçalves, Matthias Knorr, João Leite, and Jörg Pührer. Inconsistency management in reactive multi-context systems. In Loizos Michael and Antonis C. Kakas, editors, 15th European Conferenceon Logics in Artificial Intelligence (JELIA 2016), volume 10021 of Lecture Notes in Computer Science, pages 529--535, 2016. [ bib | DOI ]
We address the problem of global inconsistency in reactive multi-context systems (rMCSs), a framework for reactive reasoning in the presence of heterogeneous knowledge sources that can deal with continuous input streams. Their semantics is given in terms of equilibria streams. The occurrence of inconsistencies, where rMCSs fail to have an equilibria stream, can render the entire system useless. We discuss various methods for handling this problem, following different strategies such as repairing the rMCS, or even relaxing the notion of equilibria stream so that it can go through inconsistent states.

[7] Gerhard Brewka, Stefan Ellmauthaler, Ricardo Gonçalves, Matthias Knorr, João Leite, and Jörg Pührer. Reactive multi-context systems: Heterogeneous reasoning in dynamic environments. CoRR, abs/1609.03438, 2016. [ bib | arXiv | http ]
[8] Stefan Ellmauthaler and Jörg Pührer. Stream packing for asynchronous multi-context systems using ASP. In Thomas Eiter, Wolfgang Faber, and Stefan Woltran, editors, Proceedings of the Workshop on Trends and Applications of Answer Set Programming (TAASP 2016), 2016. [ bib | http ]
When a processing unit relies on data from external streams, we may face the problem that the stream data needs to be rearranged in a way that allows the unit to perform its task(s). On arrival of new data, we must decide whether there is sufficient information available to start processing or whether to wait for more data. Furthermore, we need to ensure that the data meets the input specification of the processing step. In the case of multiple input streams it is also necessary to coordinate which data from which incoming stream should form the input of the next process instantiation. In this work, we propose a declarative approach as an interface between multiple streams and a processing unit. The idea is to specify via answer-set programming how to arrange incoming data in packages that are suitable as input for subsequent processing. Our approach is intended for use in asynchronous multi-context systems (aMCSs), a recently proposed framework for loose coupling of knowledge representation formalisms that allows for online reasoning in a dynamic environment. Contexts in aMCSs process data streams from external sources and other contexts.

[9] Gerhard Brewka, Stefan Ellmauthaler, Ricardo Gonçalves, Matthias Knorr, João Leite, and Jörg Pührer. Towards inconsistency management in reactive multi-context systems. In Richard Booth, Giovanni Casini, Szymon Klarman, Gilles Richard, and Ivan José Varzincza, editors, Proceedings of the International Workshop on Defeasible and Ampliative Reasoning (DARe-16) co-located with the 22th European Conference on Artificial Intelligence (ECAI 2016), The Hague, Holland, August 29, 2016., CEUR Workshop Proceedings. CEUR-WS.org, 2016. [ bib | .pdf ]
In this paper, we begin by introducing reactive multicontext systems (rMCSs), a framework for reactive reasoning in the presence of heterogeneous knowledge sources. In particular, we show how to integrate data streams into multi-context systems (MCSs) and how to model the dynamics of the systems, based on two types of bridge rules. We then discuss various methods for handling inconsistencies, a problem that occurs with reasoning based on multiple knowledge sources that need to be integrated, with a special focus on non-existence of equilibria.

[10] Stefan Ellmauthaler and Jörg Pührer. Asynchronous multi-context systems. In Thomas Eiter, Hannes Strass, Miroslaw Truszczynski, and Stefan Woltran, editors, Advances in Knowledge Representation, Logic Programming, and Abstract Argumentation - Essays Dedicated to Gerhard Brewka on the Occasion of His 60th Birthday, volume 9060 of Lecture Notes in Computer Science. Springer, 2015. [ bib | DOI | http ]
We present asynchronous multi-context systems (aMCSs), a framework for loosely coupling different knowledge representation formalisms that allows for online reasoning in a dynamic environment. An aMCS interacts with the outside world via input and output streams and may therefore react to a continuous flow of external information. In contrast to recent proposals, contexts in an aMCS communicate with each other in an asynchronous way which fits the needs of many application domains and is beneficial for scalability. The federal semantics of aMCSs renders our framework an integration approach rather than a knowledge representation formalism itself. We illustrate the introduced concepts by means of an example scenario dealing with rescue services. In addition, we compare aMCSs to reactive multi-context systems and describe how to simulate the latter with our novel approach.

[11] Stefan Ellmauthaler and Hannes Strass. The DIAMOND system for computing with abstract dialectical frameworks. In Simon Parsons, Nir Oren, Chris Reed, and Federico Cerutti, editors, 5th International Conference on Computational Models of Argument (COMMA 2014), volume 266 of Frontiers in Artificial Intelligence and Applications, pages 233--240. IOS Press, September 2014. [ bib | DOI | .pdf ]
We present diamond, an implementation of Brewka and Woltran's abstract dialectical frameworks (ADFs). The system uses answer set programming encodings to compute interpretations of ADFs according to various semantics. We evaluate the performance of the system using an actual reasoning problem as opposed to using randomly generated frameworks.

[12] Stefan Ellmauthaler and Jörg Pührer. Asynchronous multi-context systems. In Stefan Ellmauthaler and Jörg Pührer, editors, International Workshop on Reactive Concepts in Knowledge Representation (ReactKnow 2014), pages 31--38, 2014. [ bib | http ]
In this work, we present asynchronous multi-context systems (aMCSs), which provide a framework for loosely coupling different knowledge representation formalisms that allows for online reasoning in a dynamic environment. Systems of this kind may interact with the outside world via input and output streams and may therefore react to an continuous flow of external information. In contrast to recent proposals, contexts in an aMCS communicate with each other in an asynchronous way which fits the needs of many application domains and results is beneficial for scalability. The federal semantics of aMCSs render our framework an integration approach rather than a knowledge representation formalism itself. We illustrate the introduced concepts by means of an example scenario dealing with rescue services. In addition we compare aMCSs to reactive multi-context systems and describe how to simulate the latter with our novel approach.

[13] Gerhard Brewka, Stefan Ellmauthaler, and Jörg Pührer. Mulit-context systems for reactive reasoning in dynamic environments. In Stefan Ellmauthaler and Jörg Pührer, editors, International Workshop on Reactive Concepts in Knowledge Representation (ReactKnow 2014), pages 23--30, 2014. [ bib | http ]
We show in this paper how managed multi-context systems (mMCS) can be turned into a reactive formalism suitable for continuous reasoning in dynamic environments. We extend mMCS with (abstract) sensors and define the notion of a run of the extended systems. We then show how typical problems arising in online reasoning can be addressed: handling potentially inconsistent sensor input, modeling intelligent forms of forgetting, selective integration of knowledge, and controlling the reasoning effort spent by contexts, like setting contexts to an idle mode. We also investigate the complexity of some important related decision problems and discuss different design choices which are given to the knowledge engineer.

[14] Gerhard Brewka, Stefan Ellmauthaler, and Jörg Pührer. Multi-context systems for reactive reasoning in dynamic environments. In Torsten Schaub, Gerhard Friedrich, and Barry O'Sullivan, editors, 21st European Conference on Artificial Intelligence (ECAI 2014), volume 263 of Frontiers in Artificial Intelligence and Applications, pages 159--164. IOS Press, 2014. [ bib | DOI ]
We show in this paper how managed multi-context systems (mMCS) can be turned into a reactive formalism suitable for continuous reasoning in dynamic environments. We extend mMCS with (abstract) sensors and define the notion of a run of the extended systems. We then show how typical problems arising in online reasoning can be addressed: handling potentially inconsistent sensor input, modeling intelligent forms of forgetting, and controlling the reasoning effort spent by contexts. We also investigate the complexity of some important related decision problems.

[15] Stefan Ellmauthaler. Generalizing multi-context systems for reactive stream reasoning applications. In Andrew V. Jones and Nicholas Ng, editors, Proceedings of the 2013 Imperial College Computing Student Workshop (ICCSW 2013), OpenAccess Series in Informatics (OASIcs), pages 17--24. Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik, September 2013. [ bib | DOI | http | .pdf ]
In the field of artificial intelligence (AI), the subdomain of knowledge representation (KR) has the aim to represent, integrate, and exchange knowledge in order to do some reasoning about the given information. During the last decades many different KR-languages were proposed for a variety of certain applications with specific needs. The concept of a managed Multi-Context System (mMCS) was introduced to provide adequate formal tools to interchange and integrate knowledge between different KR-approaches. Another arising field of interest in computer science is the design of online applications, which react directly to (possibly infinite) streams of information. This paper presents a genuine approach to generalize mMCS for online applications with continuous streams of information. Our major goal is to find a good tradeoff between expressiveness and computational complexity.

[16] Stefan Ellmauthaler and Hannes Strass. The DIAMOND system for argumentation: Preliminary report. In Michael Fink and Yuliya Lierler, editors, Proceedings of the 6th International Workshop on Answer Set Programming and Other Computing Paradigms (ASPOCP 2013), volume abs/1312.6140, September 2013. [ bib | .pdf ]
Abstract dialectical frameworks (ADFs) are a powerful generalisation of Dung's abstract argumentation frameworks. In this paper we present an answer set programming based software system, called DIAMOND (DIAlectical MOdels eNcoDing). It translates ADFs into answer set programs whose stable models correspond to models of the ADF with respect to several semantics (i.e. admissible, complete, stable, grounded).

[17] Gerhard Brewka, Stefan Ellmauthaler, Hannes Strass, Johannes Peter Wallner, and Stefan Woltran. Abstract dialectical frameworks revisited. In Francesca Rossi, editor, Proceedings of the 23rd International Joint Conference on Artificial Intelligence (IJCAI 2013). IJCAI/AAAI, August 2013. [ bib | http | .pdf ]
We present various new concepts and results related to abstract dialectical frameworks (adfs), a powerful generalization of Dung's argumentation frameworks (afs). In particular, we show how the existing definitions of stable and preferred semantics which are restricted to the subcase of so-called bipolar adfs can be improved and generalized to arbitrary frameworks. Furthermore, we introduce preference handling methods for adfs, allowing for both reasoning with and about preferences. Finally, we present an implementation based on an encoding in answer set programming.

[18] Stefan Ellmauthaler. Abstract Dialectical Frameworks: Properties, Complexity, and Implementation. Master's thesis, Technische Universität Wien, Institut für Informationssysteme, 2012. [ bib | http ]
Over the last two decades the interest for Abstract Argumentationsteadily raised in the field of Artificial Intelligence. The concept of Dung's Argumentation Frameworks (AFs), where arguments and their relations are represented in a directed graph-structure, is a well-known, simple, and powerful concept. This framework is used to find acceptable sets of arguments, which have specific properties (e.g. being conflict free), defined by several semantics. Recently Abstract Dialectical Frameworks (ADFs) were introduced, a generalization of Dung's approach, to overcome the limitation of attack-relations being the only type of native relations. To reach this goal, in addition to the relations, total functions are used to decide the acceptance of an argument. These functions are so called acceptance conditions. Due to the high expressiveness of this newly proposed theory, some semantics were only generalized for the restricted bipolar ADFs yet. This work will give an exhaustive overview on ADFs. The restriction to bipolar ADFs for some of the semantics is not desired, so we try to develop a solution to gain the generalized stable model semantics. This semantics is particularly important because the other semantics which are restricted to bipolar ADFs, depend on stable models. To gain such a generalization, we will try to connect the foundations of ADFs to other fields of computer science. So we may relate subclasses of these fields to the bipolar ADF to overcome this obstacle. This connection also makes ADFs more accessible to other fields of computer science. We will concentrate mainly on the introduction of the alternative representation of propositional-formula ADFs (pForm-ADFs), but we will also show that ADFs can be represented as hyper-graphs. Based on the new representation a transformation from ADFs to pForm-ADFs, together with a generalization of the stable model semantics will be presented. In addition some properties between semantics will be investigated and an overview of complexity results, enriched with new ones is given. Currently there is no software system available to compute semantics for ADFs. So in addition to the formal results we also present an Answer Set Programming (ASP) based implementation to solve these highly complex computations. We will also present preliminary empirical experiments.

[19] Stefan Ellmauthaler and Johannes Peter Wallner. Evaluating Abstract Dialectical Frameworks with ASP. In Bart Verheij, Stefan Szeider, and Stefan Woltran, editors, 4th International Conference on Computational Models of Argument (COMMA 2012), volume 245, pages 505--506. IOS Press, 2012. [ bib | .pdf ]

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