Hannes Strass’s research while affiliated with TU Dresden and other places

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Publications (62)


Consequence Operators of Characterization Logics – The Case of Abstract Argumentation
  • Chapter

October 2024

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5 Reads

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Hannes Strass

Risk Management for Medical Devices via the Riskman Ontology & Shapes

May 2024

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34 Reads

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Martin Diller

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[...]

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Hannes Strass

We introduce the Riskman ontology & shapes for representing and analysing information about risk management for medical devices. Risk management is concerned with taking necessary precautions so a medical device does not cause harms for users or the environment. To date, risk management documentation is submitted to notified bodies (for certification) in the form of semi-structured natural language text. We propose to use classes from the Riskman ontology to logically model risk management documentation and to use the included SHACL constraints to check for syntactic completeness and conformity to relevant standards. In particular, the ontology is modelled after ISO 14971 and the recently published VDE Spec 90025. Our proposed methodology has the potential to save many person-hours for both manufacturers (when creating risk management documentation) as well as notified bodies (when assessing submitted applications for certification), and thus offers considerable benefits for healthcare and, by extension, society as a whole.


Pushing the Boundaries of Tractable Multiperspective Reasoning: A Deduction Calculus for Standpoint EL+

September 2023

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5 Reads

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6 Citations

Standpoint EL is a multi-modal extension of the popular description logic EL that allows for the integrated representation of domain knowledge relative to diverse standpoints or perspectives. Advantageously, its satisfiability problem has recently been shown to be in PTime, making it a promising framework for large-scale knowledge integration. In this paper, we show that we can further push the expressivity of this formalism, arriving at an extended logic, called Standpoint EL+, which allows for axiom negation, role chain axioms, self-loops, and other features, while maintaining tractability. This is achieved by designing a satisfiability-checking deduction calculus, which at the same time addresses the need for practical algorithms. We demonstrate the feasibility of our calculus by presenting a prototypical Datalog implementation of its deduction rules.


Tractable Diversity: Scalable Multiperspective Ontology Management via Standpoint EL

August 2023

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6 Reads

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10 Citations

The tractability of the lightweight description logic EL has allowed for the construction of large and widely used ontologies that support semantic interoperability. However, comprehensive domains with a broad user base are often at odds with strong axiomatisations otherwise useful for inferencing, since these are usually context dependent and subject to diverging perspectives. In this paper we introduce Standpoint EL, a multi-modal extension of EL that allows for the integrated representation of domain knowledge relative to diverse, possibly conflicting standpoints (or contexts), which can be hierarchically organised and put in relation to each other. We establish that Standpoint EL still exhibits EL's favourable PTime standard reasoning, whereas introducing additional features like empty standpoints, rigid roles, and nominals makes standard reasoning tasks intractable.


Automated reasoning support for Standpoint-OWL 2
  • Preprint
  • File available

April 2023

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25 Reads

We present a tool for modelling and reasoning with knowledge from various diverse (and possibly conflicting) viewpoints. The theoretical underpinnings are provided by enhancing base logics by standpoints according to a recently introduced formalism that we also recall. The tool works by translating the standpoint-enhanced version of the description logic SROIQ to its plain (i.e. classical) version. Existing reasoners can then be directly used to provide automated support for reasoning about diverse standpoints.

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Pushing the Boundaries of Tractable Multiperspective Reasoning: A Deduction Calculus for Standpoint EL+

April 2023

·

38 Reads

Standpoint EL is a multi-modal extension of the popular description logic EL that allows for the integrated representation of domain knowledge relative to diverse standpoints or perspectives. Advantageously, its satisfiability problem has recently been shown to be in PTime, making it a promising framework for large-scale knowledge integration. In this paper, we show that we can further push the expressivity of this formalism, arriving at an extended logic, called Standpoint EL+, which allows for axiom negation, role chain axioms, self-loops, and other features, while maintaining tractability. This is achieved by designing a satisfiability-checking deduction calculus, which at the same time addresses the need for practical algorithms. We demonstrate the feasibility of our calculus by presenting a prototypical Datalog implementation of its deduction rules.


How to Agree to Disagree: Managing Ontological Perspectives using Standpoint Logic

October 2022

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37 Reads

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3 Citations

Lecture Notes in Computer Science

The importance of taking individual, potentially conflicting perspectives into account when dealing with knowledge has been widely recognised. Many existing ontology management approaches fully merge knowledge perspectives, which may require weakening in order to maintain consistency; others represent the distinct views in an entirely detached way. As an alternative, we propose Standpoint Logic , a simple, yet versatile multi-modal logic “add-on” for existing KR languages intended for the integrated representation of domain knowledge relative to diverse, possibly conflicting standpoints , which can be hierarchically organised, combined, and put in relation with each other. Starting from the generic framework of First-Order Standpoint Logic (FOSL), we subsequently focus our attention on the fragment of sentential formulas, for which we provide a polytime translation into the standpoint-free version. This result yields decidability and favourable complexities for a variety of highly expressive decidable fragments of first-order logic. Using some elaborate encoding tricks, we then establish a similar translation for the very expressive description logic SROIQbs\mathcal {SROIQ}b_s SROIQ b s underlying the OWL 2 DL ontology language. By virtue of this result, existing highly optimised OWL reasoners can be used to provide practical reasoning support for ontology languages extended by standpoint modelling.


How to Agree to Disagree: Managing Ontological Perspectives using Standpoint Logic

June 2022

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30 Reads

The importance of taking individual, potentially conflicting perspectives into account when dealing with knowledge has been widely recognised. Many existing ontology management approaches fully merge knowledge perspectives, which may require weakening in order to maintain consistency; others represent the distinct views in an entirely detached way. As an alternative, we propose Standpoint Logic, a simple, yet versatile multi-modal logic ``add-on'' for existing KR languages intended for the integrated representation of domain knowledge relative to diverse, possibly conflicting standpoints, which can be hierarchically organised, combined and put in relation to each other. Starting from the generic framework of First-Order Standpoint Logic (FOSL), we subsequently focus our attention on the fragment of sentential formulas, for which we provide a polytime translation into the standpoint-free version. This result yields decidability and favourable complexities for a variety of highly expressive decidable fragments of first-order logic. Using some elaborate encoding tricks, we then establish a similar translation for the very expressive description logic SROIQb_s underlying the OWL 2 DL ontology language. By virtue of this result, existing highly optimised OWL reasoners can be used to provide practical reasoning support for ontology languages extended by standpoint modelling.


An Abstract, Logical Approach to Characterizing Strong Equivalence in Non-monotonic Knowledge Representation Formalisms

February 2022

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47 Reads

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12 Citations

Artificial Intelligence

Two knowledge bases are strongly equivalent if and only if they are mutually interchangeable in arbitrary contexts. This notion is of high interest for any logical formalism, since it allows to locally replace parts of a given theory without changing its meaning. In contrast to classical logic, where strong equivalence coincides with standard equivalence (having the same models), it is possible to find ordinary but not strongly equivalent objects for any nonmonotonic formalism available in the literature. Consequently, much effort has been devoted to characterizing strong equivalence for knowledge representation formalisms such as logic programs under the stable model semantics, Reiter's default logic, or Dung's argumentation frameworks. For example, strong equivalence for logic programs under stable models can be characterized by so-called HT-models. More precisely, two logic programs are strongly equivalent if and only if they are standard equivalent in the logic of here and there. This means, the logic of here and there can be seen as a characterizing formalism for logic programs under stable model semantics. The aim of this article is to study whether the existence of such characterization logics can be guaranteed for any logic. One main result is that every knowledge representation formalism that allows for a notion of strong equivalence on its finite knowledge bases also possesses a canonical characterizing formalism. In particular, we argue that those characterizing formalisms can be seen as classical, monotonic logics. Moreover, we will not only show the existence of characterizing formalism, but even that the model theory of any characterizing logic is uniquely determined (up to isomorphism).


On the Decomposition of Abstract Dialectical Frameworks and the Complexity of Naive-based Semantics

January 2021

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11 Reads

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14 Citations

Journal of Artificial Intelligence Research

dialectical frameworks (ADFs) are a recently introduced powerful generalization of Dung’s popular abstract argumentation frameworks (AFs). Inspired by similar work for AFs, we introduce a decomposition scheme for ADFs, which proceeds along the ADF’s strongly connected components. We find that, for several semantics, the decompositionbased version coincides with the original semantics, whereas for others, it gives rise to a new semantics. These new semantics allow us to deal with pertinent problems such as odd-length negative cycles in a more general setting, that for instance also encompasses logic programs. We perform an exhaustive analysis of the computational complexity of these new, so-called naive-based semantics. The results are quite interesting, for some of them involve little-known classes of the so-called Boolean hierarchy (another hierarchy in between classes of the polynomial hierarchy). Furthermore, in credulous and sceptical entailment, the complexity can be different depending on whether we check for truth or falsity of a specific statement.


Citations (41)


... Declarative rule languages are central to knowledge representation and reasoning (KRR), be it as the foundation of logic programming (Körner et al. 2022;Calimeri et al. 2020), as a design principle for ontology languages (ter Horst 2005; Motik et al. 2009;Krötzsch, Rudolph, and Hitzler 2013), or merely as a computational framework for reasoning (Gómez Álvarez, Rudolph, and Strass 2023;Simančík, Kazakov, and Horrocks 2011;Krötzsch 2011). Indeed, few logical paradigms embody such harmony of intuitive meaning, formal semantics, and practical execution. ...

Reference:

Nemo: Your Friendly and Versatile Rule Reasoning Toolkit
Pushing the Boundaries of Tractable Multiperspective Reasoning: A Deduction Calculus for Standpoint EL+
  • Citing Conference Paper
  • September 2023

... Despite the PTIME translation, it remains to be seen if this approach performs well in practical cases. An alternative would be to devise a quasimodel-based tableau algorithm along the lines of (Wolter and Zakharyaschev 1998;Gómez Álvarez, Rudolph, and Strass 2023b), yet this would be a challenging endeavour since it requires the implementation of a tailored reasoner. ...

Tractable Diversity: Scalable Multiperspective Ontology Management via Standpoint EL
  • Citing Conference Paper
  • August 2023

... As a possible alternative to extending some concepts that are currently stubs (in the sense of the stub metapattern [48]), we envision to use the novel formalism of standpoint logic [33,34] to import and attach further ontologies to Riskman. In this regard it is especially notable and useful that the combination of standpoint logic and the description logic EL retains the latter's polytime computational complexity [36,35]. ...

How to Agree to Disagree: Managing Ontological Perspectives using Standpoint Logic

Lecture Notes in Computer Science

... In the case of bipolarity of ADFs, the focus is on attacking and supporting relations between arguments, which are represented by bipolar acceptance conditions. Bipolar ADFs were first introduced by [18], and have been investigated to quite some depth later on regarding complexity issues [18,69], relations to other argumentation formalisms [61], number of bipolar acceptance conditions [7], importing ideas of bipolarity of ADFs to logic programming [4], studying expressivity of bipolar ADFs [51,66], and bipolarity was used in investigations of admissibility [62]. More generally, bipolarity in formal argumentation has, likewise, received attention from the community [21]. ...

Boolean Functions with Ordered Domains in Answer Set Programming
  • Citing Article
  • February 2016

Proceedings of the AAAI Conference on Artificial Intelligence

... The additional expressive power is achieved by adding acceptance conditions to the arguments which allow for the specification of more complex relationships between them. Of particular interest might be the subclass of bipolar ADFs (BADFs) which are as complex as AFs while arguably offering more modelling capabilities (Brewka, Ellmauthaler, Strass, Wallner, & Woltran, 2017;Straß & Wallner, 2015;Baumann & Heinrich, 2023). It is one highly relevant future task to investigate notions of forgetting in these more expressive argumentation formalisms. ...

Weighted Abstract Dialectical Frameworks
  • Citing Article
  • April 2018

Proceedings of the AAAI Conference on Artificial Intelligence

... Now let us turn to strong equivalence [25,13], i.e. how to decide whether two AFs are interchangeable in any given context without changing the semantics. More formally, in case of a labelling-based semantics L σ , two AFs F and G are strongly equivalent (denoted as F ≡ Lσ s G) if and only if L σ (F ⊔ H ) = L σ (G ⊔ H ) for any further AF H . ...

An Abstract, Logical Approach to Characterizing Strong Equivalence in Non-monotonic Knowledge Representation Formalisms

Artificial Intelligence

... Conditional independence has been investigated in several other logic-based frameworks, such as (iterated) belief revision (Lynn, Delgrande, and Peppas, 2022;Kern-Isberner, Heyninck, and Beierle, 2022), conditional logics (Heyninck, Kern-Isberner, and Meyer, 2022) and formal argumentation (Rienstra et al., 2020;Gaggl, Rudolph, and Strass, 2021). The benefit of our work is that the algebraic nature allows for the straightforward application to other formalisms with a fixpoint semantics. ...

On the Decomposition of Abstract Dialectical Frameworks and the Complexity of Naive-based Semantics
  • Citing Article
  • January 2021

Journal of Artificial Intelligence Research

... One approach to reasoning in ASPIC + consists of first explicitly constructing arguments from these building blocks, which gives rise to a corresponding abstract argumentation framework (Modgil and Prakken 2013), and then reasoning over the abstract argumentation framework in order to decide whether the conclusions of interest can be drawn (Dung 1995). However, this two-step approach is cumbersome in both theory and practice (Lehtonen, Wallner, and Järvisalo 2020) as the first step of argument construction may give rise to an exponentially larger abstract framework (Strass, Wyner, and Diller 2019). This makes it challenging to establish complexity results for ASPIC + reasoning and to develop practical algorithms. ...

EMIL: Extracting Meaning from Inconsistent Language
  • Citing Article
  • May 2019

International Journal of Approximate Reasoning

... That is, we may view φ as an independent module of Φ. Within the KR community it is folklore that this is usually not the case for non-monotonic logics (apart from folklore, we refer the reader to (Baumann and Strass 2016) for a rigorous study of this matter). ...

An Abstract Logical Approach to Characterizing Strong Equivalence in Logic-based Knowledge Representation Formalisms

... However, by definition of Boolean network, the acceptance condition of an argument depends on all the parents of that argument. Hence, contingency (11) To see this, assume that φ b depends on a, and observe that φ b is not anti-monotone on a The fact that we can transit from monotonicity to derivation through negation suggests considering strict interactions (used, for instance, in [16]) so that strict monotonicity is equivalent to the strictly positive derivative. We thus get: ...

On the number of bipolar Boolean functions

Journal of Logic and Computation