Pavlos Peppas
University of Patras, Business Administration, Faculty Member
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Answer Set Programming is a declarative problem solving approach, initially tailored to modelling problems in the area of Knowledge Representation and Reasoning. In this article, we provide a knowledge-based system, capable of... more
Answer Set Programming is a declarative problem solving approach, initially tailored to modelling problems in the area of Knowledge Representation and Reasoning. In this article, we provide a knowledge-based system, capable of representing and reasoning about legal knowledge in the context of Answer Set Programming — thus, modelling non-monotonicity that is inherent in legal arguments. The work, although limited to a specific indicative domain, namely, university regulations, has a variety of extensions. The overall approach constitutes a representative implementation of the Answer Set Programming's modelling methodology, as well as an enhancing of the bond between Artificial Intelligence and Legal Science, bringing us a step closer to a successful development of an automated legal reasoning system for real-world applications.
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Notwithstanding the extensive work on iterated belief revision, there is, still, no fully satisfactory solution within the classical AGM paradigm. The seminal work of Darwiche and Pearl (DP approach, for short) remains the most dominant,... more
Notwithstanding the extensive work on iterated belief revision, there is, still, no fully satisfactory solution within the classical AGM paradigm. The seminal work of Darwiche and Pearl (DP approach, for short) remains the most dominant, despite its well-documented shortcomings. In this article, we make further observations on the DP approach. Firstly, we prove that the DP postulates are, in a strong sense, inconsistent with Parikh's relevance-sensitive axiom (P), extending previous initial conflicts. Immediate consequences of this result are that an entire class of intuitive revision operators, which includes Dalal's operator, violates the DP postulates, as well as that the Independence postulate and Spohn's conditionalization are inconsistent with (P). Lastly, we show that the DP postulates allow for more revision polices than the ones that can be captured by identifying belief states with total preorders over possible worlds, a fact implying that a preference ordering...
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One of the main shortcomings of the early AGM paradigm is its lack of any guidelines for iterated revision; it formalizes only one-step rational belief revision. Darwiche and Pearl, subsequently, addressed this problem by introducing four... more
One of the main shortcomings of the early AGM paradigm is its lack of any guidelines for iterated revision; it formalizes only one-step rational belief revision. Darwiche and Pearl, subsequently, addressed this problem by introducing four additional postulates (the DP postulates), supplementing the AGM ones. Despite the popularity of the DP approach, there are still controversies surrounding the DP postulates. In this article, we prove a conflict between each one of the latter, and one of the most popular and intuitive "off the shelf" revision functions, that is Dalal's revision operator.
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We propose a novel architecture for holistic AI systems that integrate machine learning and knowledge representation. We extend an earlier proposal to divide representations into symbolic, conceptual and subconceptual levels. The key idea... more
We propose a novel architecture for holistic AI systems that integrate machine learning and knowledge representation. We extend an earlier proposal to divide representations into symbolic, conceptual and subconceptual levels. The key idea is to use event boards representing components of events as an analogy to blackboards found in earlier AI systems. The event components are ‘thematic roles’ such as agent, patient, recipient, action, and result. They are represented in terms of vectors of conceptual spaces rather than in symbolic form that has been used previously. A control level, including an attention mechanism decides which processes are run
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We present an account of relevance in belief revision where, intuitively, one wants to only consider the relevant part of an agent’s epistemic state in a revision. We assume that relevance is a domain-specific notion, and that... more
We present an account of relevance in belief revision where, intuitively, one wants to only consider the relevant part of an agent’s epistemic state in a revision. We assume that relevance is a domain-specific notion, and that (ir)relevance assertions are given as part of the agent’s epistemic state. Such assertions apply in a given context, and are of the form “in the case that formula σ holds, the Y part of the agent’s epistemic state is independent of the rest of the epistemic state”, where Y is part of the signature of the language. Two approaches are given, one in which (in semantic terms) conditions are placed on a faithful ranking on possible worlds to enforce the (ir)relevance assertions, and a second in which the possible worlds characterising the agent’s beliefs may be modified in a revision. These approaches are shown to yield the same resulting belief set. Corresponding postulates and a representation result are given. The overall approach is compared to that of Parikh’s...
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Research Interests: Engineering and Stairs
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Parikh’s relevance-sensitive axiom (P) for belief revision is open to two different interpretations, i.e. the weak and the strong version of (P), both of which are plausible depending on the context. Given that strong (P) has not received... more
Parikh’s relevance-sensitive axiom (P) for belief revision is open to two different interpretations, i.e. the weak and the strong version of (P), both of which are plausible depending on the context. Given that strong (P) has not received the attention it deserves, in this article, an extended examination of it is conducted. In particular, we point out interesting properties of the semantic characterization of the strong version of (P), as well as a vital feature of it that, potentially, results in a significant drop on the resources required for an implementation of a belief-revision system. Lastly, we shed light on the natural connection between global and local revision functions, via their corresponding semantic characterization, hence, a means for constructing global revision functions from local ones, and vice versa, is provided.
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This paper summarizes the approaches employed by Team UTS Unleashed! to take First Place in the 2019 RoboCup@Home Social Standard Platform League. First, our system architecture is introduced. Next, our approach to basic skills needed for... more
This paper summarizes the approaches employed by Team UTS Unleashed! to take First Place in the 2019 RoboCup@Home Social Standard Platform League. First, our system architecture is introduced. Next, our approach to basic skills needed for a strong performance in the competition. We describe several implementations for tests participation. Finally our software development methodology is discussed.
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Research Interests: Bioinformatics, Computer Science, Physics, Dynamical Systems, Complex Systems, and 15 moreComplexity, Cellular Automata, Dynamical systems and Chaos, Medicine, Multidisciplinary, Formal Semantics, Chaos, Negation, Edge of Chaos, Novelty, Stability and Chaos, Diagonalization, Self reference, Formal Systems, and Halting Problem
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Possible-world semantics are provided for Parikh's relevance-sensitive axiom for belief revision, known as axiom (P). Loosely speaking, axiom (P) states that if a belief set K can be divided into two disjoint compartments, and the new... more
Possible-world semantics are provided for Parikh's relevance-sensitive axiom for belief revision, known as axiom (P). Loosely speaking, axiom (P) states that if a belief set K can be divided into two disjoint compartments, and the new information ? relates only to the first compartment, then the second compartment should not be effected by the revision of K by ?. Using the well-known connection between AGM revision functions and preorders on possible worlds as our starting point, we formulate additional constraints on such preorders that characterise precisely Parikh's axiom (P). Interestingly, the additional constraints essentially generalise a criterion of plausibility between possible worlds that predates axiom (P). A by-product of our study is the identification of two possible readings of Parikh's axiom (P), which we call the strong and the weak versions of the axiom. Regarding specific operators, we show that Dalal's belief revision operator satisfies both weak and strong (P), and it is therefore relevance-sensitive.
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In applying circumscription to minimise fluent change in the logic of actions, we could either let the Holds predicate vary, or let the Result function vary. We show that the solutions of the latter are included in that of the former when... more
In applying circumscription to minimise fluent change in the logic of actions, we could either let the Holds predicate vary, or let the Result function vary. We show that the solutions of the latter are included in that of the former when viewed from an input-output perspective. This is ...
In this paper we aim at giving a formal characterization of the notion of responsibility in multi-agent systems. A clearer view of responsibility is critical for regulating multiagent settings: to understand what kinds of responsibility... more
In this paper we aim at giving a formal characterization of the notion of responsibility in multi-agent systems. A clearer view of responsibility is critical for regulating multiagent settings: to understand what kinds of responsibility are at stake in a given scenario can help predict system's future behaviour and improve its efficiency. However, although attempts of formal theories of responsibility are increasing, they usually reduce it to causation, while we underline the importance of a theory of responsibility before a damage could ever take ...
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The policy of rational belief revision is encoded in the so-called AGM revision functions. Such functions are characterized (both axiomatically and constructively) within the well-known AGM paradigm, proposed by Alchourrón, Gärdenfors and... more
The policy of rational belief revision is encoded in the so-called AGM revision functions. Such functions are characterized (both axiomatically and constructively) within the well-known AGM paradigm, proposed by Alchourrón, Gärdenfors and Makinson. In this article, we show that — although not in a straightforward way — a sufficient extension of the underlying language allows for the modelling of any AGM revision function (defined at the initial language), by means of a Hamming-based rule for belief revision introduced by Dalal (defined at the extended language). The established results enrich the applicability of Dalal’s proposal, leading to a conceptual and ontological reduction, as well as open new doors for the construction of any type of revision function in a practical context, given the intuitive appeal and simplicity of Dalal’s construction.
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The AGM paradigm for belief change, as originally introduced by Alchourron, Gärdenfors and Makinson, lacks any guidelines for the process of iterated revision. One of the most influential work addressing this problem is Darwiche and... more
The AGM paradigm for belief change, as originally introduced by Alchourron, Gärdenfors and Makinson, lacks any guidelines for the process of iterated revision. One of the most influential work addressing this problem is Darwiche and Pearl's approach (DP approach, for short), which, despite its well-documented shortcomings, remains to this date the most dominant. In this article, we make further observations on the DP approach. In particular, we prove that the DP postulates are, in a strong sense, inconsistent with Parikh's relevance-sensitive axiom (P), extending previous initial conflicts. Immediate consequences of this result are that an entire class of intuitive revision operators, which includes Dalal's operator, violates the DP postulates, as well as that the Independence postulate and Spohn's conditionalization are inconsistent with axiom (P). The whole study, essentially, indicates that two fundamental aspects of the revision process, namely, iteration and rel...
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In this paper we explore several fundamental relations between formal systems, algorithms, and dynamical systems, focussing on the roles of undecidability, universality, diagonalization, and self-reference in each of these computational... more
In this paper we explore several fundamental relations between formal systems, algorithms, and dynamical systems, focussing on the roles of undecidability, universality, diagonalization, and self-reference in each of these computational frameworks. Some of these interconnections are well-known, while some are clarified in this study as a result of a fine-grained comparison between recursive formal systems, Turing machines, and Cellular Automata (CAs). In particular, we elaborate on the diagonalization argument applied to distributed computation carried out by CAs, illustrating the key elements of G¨odel’s proof for CAs. The comparative analysis emphasizes three factors which underlie the capacity to generate undecidable dynamics within the examined computational frameworks: (i) the program-data duality; (ii) the potential to access an infinite computational medium; and (iii) the ability to implement negation. The considered adaptations of Godel’s proof distinguish between computational universality and undecidability, and show how the diagonalization argument exploits, on several levels, the self-referential basis of undecidability.
Research Interests: Dynamical Systems, Complex Systems, Complexity, Cellular Automata, Self-Reference, Reflexivity, Reflection, and 15 moreDynamical systems and Chaos, Chaos/Complexity Theory, Formal Semantics, Gödel's Incompleteness Theorems, Chaos, Self-Reference, Edge of Chaos, Novelty, Turing machine, Stability and Chaos, Diagonalization, Formal Systems, Novelty-Related Behavior, Halting Problem, and Undecidablity
Summary: This paper presents a method for modeling users' perception of software quality. The method aims to improve the quality of data derived from user opinion surveys and facilitate the analysis of such data. Additionally, using... more
Summary: This paper presents a method for modeling users' perception of software quality. The method aims to improve the quality of data derived from user opinion surveys and facilitate the analysis of such data. Additionally, using aspects of Belief Revision theory, the proposed model offers a way to measure users' opinion in early stages of product release and a way
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Summary: Surveys measuring users' opinion of software quality serve not only as indications of users' satisfaction with a software product, but they also permit a more sophisticated degree of analysis required by organisations... more
Summary: Surveys measuring users' opinion of software quality serve not only as indications of users' satisfaction with a software product, but they also permit a more sophisticated degree of analysis required by organisations with higher levels of quality maturity. However, in surveys, some difficulties arise related to the quality of data, the high cost of conducting the survey and the
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ABSTRACT
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Possible-world semantics are provided for Parikh's relevance-sensitive model for belief revision. Having Grove's system-of-spheres construction as a base, we consider additional constraints on measuring distance between possible... more
Possible-world semantics are provided for Parikh's relevance-sensitive model for belief revision. Having Grove's system-of-spheres construction as a base, we consider additional constraints on measuring distance between possible worlds, and we prove that, in the pres- ence of the AGM postulates, these constraints character- ize precisely Parikh's axiom (P). These additional con- straints essentially generalize a criterion of similarity that predates
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Summary: This paper presents a method for modeling users' perception of software quality. The method aims to improve the quality of data derived from user opinion surveys and facilitate the analysis of such data. Additionally, using... more
Summary: This paper presents a method for modeling users' perception of software quality. The method aims to improve the quality of data derived from user opinion surveys and facilitate the analysis of such data. Additionally, using aspects of Belief Revision theory, the proposed model offers a way to measure users' opinion in early stages of product release and a way
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ABSTRACT
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Logic-based approaches to reasoning about actions, change and causality, highlight efficient representation and processing of domain background knowledge as an important task. Action theories recently developed in the framework of action... more
Logic-based approaches to reasoning about actions, change and causality, highlight efficient representation and processing of domain background knowledge as an important task. Action theories recently developed in the framework of action languages with inertia and ramifications [20,14] not only adopt the principle of minimal change reinforced with the policy of categorisation (assigning different degrees of inertia to language elements) but
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Abstract. A unifying semantic framework for different reasoning approaches provides an ideal tool to compare these competing alternatives. However, it has been shown recently that a pure preferential semantics alone is not capable of... more
Abstract. A unifying semantic framework for different reasoning approaches provides an ideal tool to compare these competing alternatives. However, it has been shown recently that a pure preferential semantics alone is not capable of providing such a unifying framework. On ...
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ABSTRACT This paper investigates belief revision where the underlying logic is that governing Horn clauses. We show that classical (AGM) belief revision doesn't immediately generalise to the Horn case. In particular, a standard... more
ABSTRACT This paper investigates belief revision where the underlying logic is that governing Horn clauses. We show that classical (AGM) belief revision doesn't immediately generalise to the Horn case. In particular, a standard construction based on a total preorder over possible worlds may violate the accepted (AGM) postulates. Conversely, in the obvious extension to the AGM approach, Horn revision functions are not captured by total preorders over possible worlds. We address these difficulties by introducing two modifications to the AGM approach. First, the semantic construction is restricted to “well behaved” orderings, what we call Horn compliant orderings. Second, the revision postulates are augmented by an additional postulate. Both restrictions are redundant in the AGM approach, but not in the Horn case. In a representation result we show that the class of revision functions captured by Horn compliant total preorders over possible worlds is precisely that given by the (extended) set of Horn revision postulates. Further, we show that Horn revision is compatible with work in iterated revision and work concerning relevance in revision. We also consider specific revision operators. Arguably this work is interesting for several reasons. It extends AGM revision to inferentially-weaker Horn theories; hence it sheds light on the theoretical underpinnings of belief change, as well as generalising the AGM paradigm. Thus, this work is relevant to revision in areas that employ Horn clauses, such as deductive databases and logic programming, as well as areas in which inference is weaker than classical logic, such as in description logic.