Logics for Knowledge Representation

We investigate the problem of checking the consistency of qualitative preferences expressed in CP-theory. This problem is PSPACE-Complete even when the preferences are locally consistent or the preference variables have binary domain. We present a new sufficient condition for consistency of preferences and show that the condition can be checked in polynomial time in settings of practical relevance (locally consistent or binary domain preference variables). We further show how the resulting sufficient condition can be used to efficiently identify a subset of outcomes that are non-dominated with respect to a set of qualitative preferences.

We show that subsumption problems in EL and related description logics can be expressed as uniform word problems in classes of semilattices with monotone operators. We use possibilities of efficient local reasoning in such classes of algebras to obtain uniform PTIME decision procedures for CBox subsumption in EL and extensions thereof. These locality considerations allow us to present a new family of logics which extend EL and EL + with n-ary roles and/or numerical domains. Definition 1. Let C be a CBox, and C 1 , C 2 two concept descriptions. Then C 1 C C 2 if and only if C I 1 ⊆C I 2 for every model I of C.

This paper presents an initial study of the relevant issues on the development of an automated mediation agent. The work is conducted within the 'curious negotiator' framework . The paper demonstrates that mediation is a knowledge intensive process that integrates information revelation and analogical reasoning. The introduced formalism is used to demonstrate how via revealing the appropriate information and reshaping the set of issues of the disputing parties mediation can succeed. The paper presents MediaThor -a mediating agent that utilises past experiences and information from negotiating parties to mediate disputes and change the positions of negotiating parties.

In this work we focus on extensions of Description Logics (DLs) of typicality by means of probabilities. We introduce a novel extension of the logic of typicality ALC + T R , able to represent and reason about typical properties and defeasible inheritance in DLs. The novel logic (ALCT P : Typical ALC with Probabilities as Proportions) allows inclusions of the form T(C) p D, with probability p representing a proportion, meaning that "all the typical Cs are Ds, and the probability that a C element is not a D element is 1 − p". We also compare and confront this novel logic with a similar one already presented in the literature (T CL , introduced in Lieto and Pozzato (2020, J. Exp. Theor. Artif. Intell., 32, 769-804)), inspired by the DISPONTE semantics and that allows inclusions of the form p : T(C) D with probability p, where p represents a degree of belief, whose meaning is that "we believe with a degree p that typical Cs' are also Ds.". We then show that the proposed ALCT P extension (like the previous T CL) can be applied in order to tackle a specific and challenging problem in the field of common-sense reasoning, namely the combination of prototypical concepts, that have been shown to be problematic to model for other symbolic approaches like fuzzy logic. We show that, for the proposed extension, the complexity of reasoning remains EXPTIME-complete as for the underlying standard monotonic DL ALC.

Artificial agents functioning in the Semantic Web are to be capable of getting knowledge from diverse sources. This implies the capability to continuously update their knowledge bases. New stream reasoning concepts make this need even more pressing. Semantic Web ontologies are commonly represented using description logic knowledge bases. We propose an agent architecture with such features, utilizing a Dynamic Reasoning System (DRS). This explicitly portrays reasoning as a process taking place in time and allows for manipulating inconsistent knowledge bases. We sketch a procedure for user-directed ontology debugging. This same mechanism can be used for automated belief revision. We identify important research directions that may benefit from this approach.

We investigate the computational complexity of testing dominance and consistency in CP-nets. Up until now, the complexity of dominance has been determined only for restricted classes in which the dependency graph of the CP-net is acyclic. However, there are preferences of interest that define cyclic dependency graphs; these are modeled with general CP-nets. We show here that both dominance and consistency testing for general CP-nets are PSPACE-complete. The reductions used in the proofs are from STRIPS planning, and thus establish strong connections between both areas. 2 Generalized propositional CP-nets Let V = {x 1 ,. .. , x n } be a finite set of variables. For each variable x ∈ V , we assume a finite domain D x of values. An Let C be a locally-consistent GCP-net. Let V = {x 1 ,. .. , x n } be the set of variables of C. We define V = V ∪ {y 1 ,. .. , y n }, where {y 1 ,. .. , y n } ∩ V = ∅. We define a GCP-net C over V , which we will show is a CP-net. To this end, for every z ∈ V we will define conditional preference rules q + (z) : z > ¬z and q − (z) : ¬z > z to be included in C by specifying formulas q + (z) and q − (z). First, for each variable x i ∈ V , we set

In this paper, we study the problem of reasoning in description logics with variables. More specifically, we consider refreshing semantics for variables in the context of the EL description logic. We investigate a particular reasoning mechanism, namely weak subsumption, in presence of terminological cycles. Weak subsumption can be viewed as a generalization of matching and unification in presence of refreshing variables. We show that weak subsumption w.r.t. greatest fix-point semantic is EXPTIME-complete. Our main technical results are derived by establishing a correspondence between this logic and a specific form of variable automata.

In this paper, we study the problem of reasoning in description logics with variables. More specifically, we consider refreshing semantics for variables in the context of the EL description logic. We investigate a particular reasoning mechanism, namely weak subsumption, in presence of terminological cycles. Weak subsumption can be viewed as a generalization of matching and unification in presence of refreshing variables. We show that weak subsumption w.r.t. greatest fix-point semantic is EXPTIME-complete. Our main technical results are derived by establishing a correspondence between this logic and a specific form of variable automata.

Explainability in Artificial Intelligence has been revived as a topic of active research by the need of conveying safety and trust to users in the `how' and `why' of automated decision-making. Whilst a plethora of approaches have been developed for post-hoc explainability, only a few focus on how to use domain knowledge, and how this influences the understandability of an explanation from the users' perspective. In this paper we show how ontologies help the understandability of interpretable machine learning models, such as decision trees. In particular, we build on Trepan, an algorithm that explains artificial neural networks by means of decision trees, and we extend it to include ontologies modeling domain knowledge in the process of generating explanations. We present the results of a user study that measures the understandability of decision trees in domains where explanations are critical, namely, in finance and medicine. Our study shows that decision trees taking i...

We investigate graph transformations, defined using Datalog-like rules based on acyclic conjunctive two-way regular path queries (acyclic C2RPQs), and we study two fundamental static analysis problems: type checking and equivalence of transformations in the presence of graph schemas. Additionally, we investigate the problem of target schema elicitation, which aims to construct a schema that closely captures all outputs of a transformation over graphs conforming to the input schema. We show all these problems are in EXPTIME by reducing them to C2RPQ containment modulo schema; we also provide matching lower bounds. We use cycle reversing to reduce query containment to the problem of unrestricted (finite or infinite) satisfiability of C2RPQs modulo a theory expressed in a description logic. CCS CONCEPTS • Theory of computation → Logic and databases.

GraphQL is a highly popular new approach to build Web APIs. An important component of this approach is the GraphQL schema definition language (SDL). The original purpose of this language is to define a so-called GraphQL schema that specifies the types of objects that can be queried when accessing a specific GraphQL Web API. This paper focuses on the question: Can we repurpose this language to define schemas for graph databases that are based on the Property Graph model? This question is relevant because there does not exist a commonly adopted approach to define schemas for Property Graphs, and because the form in which GraphQL APIs represent their underlying data sources is very similar to the Property Graph model. To answer the question we propose an approach to adopt the GraphQL SDL for Property Graph schemas. We define this approach formally and show its fundamental properties. CCS CONCEPTS • Information systems → Graph-based database models; Integrity checking;

Many visualization frameworks for ontologies in general and for concept expressions in particular are too faithful to the syntax of the languages in which those objects are represented (e.g., RDF, OWL, DL). Model outlines depart from this tradition in that they consist of diagrams characterizing the class of models of a given concept expression. We hope this semantically-oriented visualization strategy will allow users to obtain deeper insights about the meaning of such expressions, thereby preventing errors of design or of interpretation.

The aim of this work is to provide a family of qualitative theories for spatial change in general, and for motion of spatial scenes in particular. To achieve this, we consider a spatiotemporalisation MTALC(Dx), of the well-known ALC(D) family of Description Logics (DLs) with a concrete domain: the MTALC(Dx) concepts are interpreted over infinite k-ary Σ-trees, with the nodes standing for time points, and Σ including, additionally to its uses in classical k-ary Σ-trees, the description of the snapshot of an n-object spatial scene of interest; the roles split into m + n immediate-successor (accessibility) relations, which are serial, irreflexive and antisymmetric, and of which m are general, not necessarily functional, the other n functional; the concrete domain Dx is generated by an RCC8-like spatial Relation Algebra (RA) x, and is used to guide the change by imposing spatial constraints on objects of the "followed" spatial scene, eventually at different time points of the input trees. In order to capture the expressiveness of most modal temporal logics encountered in the literature, we introduce weakly cyclic Terminological Boxes (TBoxes) of MTALC(Dx), whose axioms capture the decreasing property of modal temporal operators. We show the important result that satisfiability of an MTALC(Dx) concept with respect to a weakly cyclic TBox can be reduced to the emptiness problem of a Büchi weak alternating automaton augmented with spatial constraints. In another work, complementary to this one, also submitted to this conference, we thoroughly investigate Büchi automata augmented with spatial constraints, and provide, in particular, a translation of an alternating into a nondeterministic, and an effective decision procedure for the emptiness problem of the latter.

We show that global caching can be used with propagation of both satisfiability and unsatisfiability in a sound manner to give an EXPTIME algorithm for checking satisfiability w.r.t. a TBox in the basic description logic ALC. Our algorithm is based on a simple traditional tableau calculus which builds an and-or graph where no two nodes of the graph contain the same formula set. When a duplicate node is about to be created, we use the pre-existing node as a proxy, even if the proxy is from a different branch of the tableau, thereby building global caching into the algorithm from the start. Doing so is important since it allows us to reason explicitly about the correctness of global caching. We then show that propagating both satisfiability and unsatisfiability via the andor structure of the graph remains sound. We show that various search strategies can be used with global caching, including heuristics ones. To obtain a more efficient decision procedure for ALC, we apply several optimisation techniques. Of particular importance are the propagation of both satisfiability and unsatisfiability of a given node through the whole graph via subsetchecking between node contents. Another is the minimisation of unsatisfiable sets: that is, when the status of a node becomes unsatisfiable, we identify an (ideally minimal) inconsistent subset, and replace the content of the node with this "inconsistency" since the smaller set has a greater likelihood of propagating its unsatisfiability via subset-checking. We also use a dual procedure for maximising satisfiable sets. We do cutoffs for various search strategies, in particular, backjumping for depth-first search, by propagating "inconsistencies" and unsatisfiability through the and-or graph, and avoiding unnecessary expansions. By combining global caching, propagation and cutoffs, our framework reduces the search space more significantly than the framework of Donini and Massacci [3]. Also, the freedom to use arbitrary search heuristics significantly increases the application potential of our framework. National ICT Australia is funded by the Australian Government's Dept of Communications, Information Technology and the Arts and the Australian Research Council through Backing Australia's Ability and the ICT Centre of Excellence program.

The problem of finding envy-free allocations of indivisible goods can not always be solved; therefore, it is common to study some relaxations such as envy-free up to one good (EF1). Another property of interest for efficiency of an allocation is the Pareto Optimality (PO). Under additive utility functions, it is possible to find allocations EF1 and PO using Nash social welfare. However, to find an allocation that maximizes the Nash social welfare is a computationally hard problem. In this work we propose a polynomial time algorithm which maximizes the utilitarian social welfare and at the same time produces an allocation which is EF1 and PO in a special case of additive utility functions called buyer utility functions. Moreover, a slight modification of our algorithm produces an allocation which is envy-free up to any positively valued good (EFX).

We reformulate Pratt's tableau decision procedure of checking satisfiability of a set of formulas in PDL. Our formulation is simpler and more direct for implementation. Extending the method we give the first ExpTime (optimal) tableau decision procedure not based on transformation for checking consistency of an ABox w.r.t. a TBox in PDL (here, PDL is treated as a description logic). We also prove the new result that the data complexity of the instance checking problem in PDL is coNP-complete.

We show that global caching can be used with propagation of both satisfiability and unsatisfiability in a sound manner to give an EXPTIME algorithm for checking satisfiability w.r.t. a TBox in the basic description logic ALC. Our algorithm is based on a simple traditional tableau calculus which builds an and-or graph where no two nodes of the graph contain the same formula set. When a duplicate node is about to be created, we use the pre-existing node as a proxy, even if the proxy is from a different branch of the tableau, thereby building global caching into the algorithm from the start. Doing so is important since it allows us to reason explicitly about the correctness of global caching. We then show that propagating both satisfiability and unsatisfiability via the andor structure of the graph remains sound. We show that various search strategies can be used with global caching, including heuristics ones. To obtain a more efficient decision procedure for ALC, we apply several optimisation techniques. Of particular importance are the propagation of both satisfiability and unsatisfiability of a given node through the whole graph via subsetchecking between node contents. Another is the minimisation of unsatisfiable sets: that is, when the status of a node becomes unsatisfiable, we identify an (ideally minimal) inconsistent subset, and replace the content of the node with this "inconsistency" since the smaller set has a greater likelihood of propagating its unsatisfiability via subset-checking. We also use a dual procedure for maximising satisfiable sets. We do cutoffs for various search strategies, in particular, backjumping for depth-first search, by propagating "inconsistencies" and unsatisfiability through the and-or graph, and avoiding unnecessary expansions. By combining global caching, propagation and cutoffs, our framework reduces the search space more significantly than the framework of Donini and Massacci [3]. Also, the freedom to use arbitrary search heuristics significantly increases the application potential of our framework. National ICT Australia is funded by the Australian Government's Dept of Communications, Information Technology and the Arts and the Australian Research Council through Backing Australia's Ability and the ICT Centre of Excellence program.

The traditional two-level modeling approaches produce accidental complexities when modeling multiple abstraction levels. This problem is addressed by the emerging multi-level modeling paradigm that allows an arbitrary number of modeling levels. To date, multiple frameworks and tool implementations have been proposed, but so far there is no comprehensive comparison of commonalities and differences of design choices that have been made in those frameworks and tools. We propose a feature-based comparison framework that covers three core perspectives on multi-level modeling approaches and tools: language engineering, domain modeling and tool support, and evaluated a selected set of existing approaches and tools according to them. The framework highlights research challenges and trends for future research and its results support users to choose a specific approach depending on the application domain. The framework can also be used as a basis to map and transform between approaches.

After two years of reading and writing about four dimensionalism, I still do not feel finished! I have learned a lot, though, and this is not merely due to reading, but also widely due to the many people I have met, listened and talked to throughout the last few years. Firstly, I want to thank my supervisor Øystein Linnebo for positive supportive guidance, informative suggestions and ideas. I have always felt uplifted and positive about my thoughts and progress after our talks. There is no doubt that this essay would not be what it is without these conversations. Secondly, I would like to thank Quentin and Elena for conversations about Theodore Sider's book Four Dimensionalism, as well as our lecturer Ephraim Glick for insights into the topics of three and four dimensionalism. Our semester together gave me a fantastic foundation for my dissertation. Another important person in the start of my work was my first and temporary supervisor Professor Olav Gjelsvik. Thank you for guidance on my topic and first draft. I also want to give a big thanks to Jørgen Dyrstad, Sivert Thomas Ellingsen, Mariona Sturm, Julie Lauvsland and Margrete Haldorsen Nygaard for reading and commenting on my text. Your suggestions have contributed to raising the quality of my essay.

In this paper we introduce a negotiation mediator in a multiagent context. When negotiation fails, a mediator can interact with the parties, find out about their goals, ontologies, and arguments for and against negotiation outcome, and suggest solutions based on previous experience. An algorithmic schema to be instantiated with particular argumentation, semantic alignment and case-base reasoning techniques is presented. The proposal is neutral with respect to which particular technique is selected. An example illustrates the approach that is framed in the existing body of literature on argumentation and mediation.

An approach for scene understanding based on qualitative descriptors, domain knowledge and logics is proposed in this paper. Qualitative descriptors, qualitative models of shape, colour, topology and location are used for describing any object in the scene. Two kinds of domain knowledge are provided: (i) categorizations of objects according to their qualitative descriptors, and (ii) semantics for describing the affordances, mobility and other functional properties of target objects. First order logics are obtained for reasoning and scene understanding. Tests were carried out at the Interact@Cartesium scenario and promising results were obtained.

Our approach describes any digital image qualitatively by detecting regions/objects inside it and describing their visual characteristics (shape and colour) and their spatial characteristics (orientation and topology) by means of qualitative models. The description obtained is translated into a description logic (DL) based ontology, which gives a formal and explicit meaning to the qualitative tags representing the visual features of the objects in the image and the spatial relations between them. For any image, our approach obtains a set of individuals that are classified using a DL reasoner according to the descriptions of our ontology.

There are two major formalisms that are developed around concepts. The first one is Formal Concept Analysis (FCA) by R. Wille and B. Ganter. Roughly speaking, FCA is an extension of algebraic Lattice Theory for knowledge representation. The second formalism, Description Logic (DL), goes back to the universal terminological logic by P.F. Patel-Schneider. It is closely related to modal and program logics. DL is widely used for ontology research, design, and implementation. Since both formalism use concepts and are used for closely related purposes, it is very natural to compare and combine them. In this paper we introduce and study variants of DL extended by three constructs motivated by FCA. Intentional semantics of two of the new constructs are new modalities that correspond to 'intent' and 'extent' (two major algebraic constructions of FCA). The third new construct is a connective that is designed to express the 'formal concept' property. If L is a variant of DL then we call L extended by these new constructs by L for FCA and denote this logic by L/FCA. We compare expressive powers of L/FCA and L(¬, −)-another variant of L extended by role complement ¬ and inverse − simultaneously. We demonstrate that L/FCA can be expressed in L(¬, −). It implies that for the basic description logic ALC, ALC/FCA is decidable. 1 Basic Description Logics Description logics [2] has originated from the universal terminological logic [9]. There exists many variants of description logics, but we will define only some of them in this section 1. Definition 1. Syntax of every description logic is constructed from disjoint alphabets of concept, role, and object symbols CS, RS, and OS, respectively. The This research is supported in parts by joint grant RFBR 05-01-04003-a-DFG project COMO, GZ: 436 RUS 113/829/0-1, by grant RFBR 06-01-00464-a, and Integration Grant n.14 Siberia Branch, Russian Academy of Science. 1 We give detailed definition of description logics for avoiding ambiguities, since there exists some difference in syntax notation between different research groups.

We define a modular multi-concept extension of the lexicographic closure semantics for defeasible description logics with typicality. The idea is that of distributing the defeasible properties of concepts into different modules, according to their subject, and of defining a notion of preference for each module based on the lexicographic closure semantics. The preferential semantics of the knowledge base can then be defined as a combination of the preferences of the single modules. The range of possibilities, from fine grained to coarse grained modules, provides a spectrum of alternative semantics.

In several subject domains, classes themselves may be subject to categorization, resulting in classes of classes (or "metaclasses"). When representing these domains, one needs to capture not only entities of different classification levels, but also their (intricate) relations. We observe that this is challenging in current Semantic Web languages, as there is little support to guide the modeler in producing correct multi-level ontologies, especially because of the nuances in the constraints that apply to entities of different classification levels and their relations. In order to address these representation challenges, we propose a vocabulary that can be used as a basis for multi-level ontologies in OWL along with a number of integrity constraints to prevent the construction of inconsistent models. In this process we employ an axiomatic theory called MLT (a Multi-Level Modeling Theory).

By allowing relationship types defined on top of relationship types, the Higher-Order Entity Relationship Model (HERM) enables modeling of complex conceptual structures in a layered way, which usually results in a more compact design than the traditional Entity-Relationship model. Identification of data instances is achieved by composition of the (inherited) key attributes of the referenced instances (foreign keys becoming part of natural keys of higher-order relationships). Well-formedness excludes cycles in the structure. In this paper, we look at the possibility to relax this by allowing structural recursion in the conceptual model. Although it is formally represented as a cycle in the type structure, it will not allow any cycle on the instance (data) level. After looking at some motivating cases and conventional alternatives to this design, and conditions when such a modeling decision is reasonable, we will show how a structurally recursive HERM model can be transformed into an equivalent, conventionally well-formed HERM model, with the utilization of list type construction and complex, variable-length key domains. The analysis reveals some non-trivial aspects of the way of transformation, which may be easily overlooked, but are important to formulate a translation rule for the general case, where derived attributes and aggregation needs are present. The result can be used as a rule for conceptual schema translation for structuring, to obtain an intermediate schema ready for further optimization, and eventually, code generation.

By allowing relationship types defined on top of relationship types, the Higher-Order Entity Relationship Model (HERM) enables modeling of complex conceptual structures in a layered way, which usually results in a more compact design than the traditional Entity-Relationship model. Identification of data instances is achieved by composition of the (inherited) key attributes of the referenced instances (foreign keys becoming part of natural keys of higher-order relationships). Well-formedness excludes cycles in the structure. In this paper, we look at the possibility to relax this by allowing structural recursion in the conceptual model. Although it is formally represented as a cycle in the type structure, it will not allow any cycle on the instance (data) level. After looking at some motivating cases and conventional alternatives to this design, and conditions when such a modeling decision is reasonable, we will show how a structurally recursive HERM model can be transformed into an equivalent, conventionally well-formed HERM model, with the utilization of list type construction and complex, variable-length key domains. The analysis reveals some non-trivial aspects of the way of transformation, which may be easily overlooked, but are important to formulate a translation rule for the general case, where derived attributes and aggregation needs are present. The result can be used as a rule for conceptual schema translation for structuring, to obtain an intermediate schema ready for further optimization, and eventually, code generation.

We investigate graph transformations, defined using Datalog-like rules based on acyclic conjunctive two-way regular path queries (acyclic C2RPQs), and we study two fundamental static analysis problems: type checking and equivalence of transformations in the presence of graph schemas. Additionally, we investigate the problem of target schema elicitation, which aims to construct a schema that closely captures all outputs of a transformation over graphs conforming to the input schema. We show all these problems are in EXPTIME by reducing them to C2RPQ containment modulo schema; we also provide matching lower bounds. We use cycle reversing to reduce query containment to the problem of unrestricted (finite or infinite) satisfiability of C2RPQs modulo a theory expressed in a description logic. CCS CONCEPTS • Theory of computation → Logic and databases.

We show that global caching can be used with propagation of both satisfiability and unsatisfiability in a sound manner to give an EXPTIME algorithm for checking satisfiability w.r.t. a TBox in the basic description logic ALC. Our algorithm is based on a simple traditional tableau calculus which builds an and-or graph where no two nodes of the graph contain the same formula set. When a duplicate node is about to be created, we use the pre-existing node as a proxy, even if the proxy is from a different branch of the tableau, thereby building global caching into the algorithm from the start. Doing so is important since it allows us to reason explicitly about the correctness of global caching. We then show that propagating both satisfiability and unsatisfiability via the andor structure of the graph remains sound. We show that various search strategies can be used with global caching, including heuristics ones. To obtain a more efficient decision procedure for ALC, we apply several optimisation techniques. Of particular importance are the propagation of both satisfiability and unsatisfiability of a given node through the whole graph via subsetchecking between node contents. Another is the minimisation of unsatisfiable sets: that is, when the status of a node becomes unsatisfiable, we identify an (ideally minimal) inconsistent subset, and replace the content of the node with this "inconsistency" since the smaller set has a greater likelihood of propagating its unsatisfiability via subset-checking. We also use a dual procedure for maximising satisfiable sets. We do cutoffs for various search strategies, in particular, backjumping for depth-first search, by propagating "inconsistencies" and unsatisfiability through the and-or graph, and avoiding unnecessary expansions. By combining global caching, propagation and cutoffs, our framework reduces the search space more significantly than the framework of Donini and Massacci [3]. Also, the freedom to use arbitrary search heuristics significantly increases the application potential of our framework. National ICT Australia is funded by the Australian Government's Dept of Communications, Information Technology and the Arts and the Australian Research Council through Backing Australia's Ability and the ICT Centre of Excellence program.

A multiagent system may be thought of as an artificial society of autonomous software agents and we can apply concepts borrowed from welfare economics and social choice theory to assess the social welfare of such an agent society. In this paper, we study an abstract negotiation framework where agents can agree on multilateral deals to exchange bundles of indivisible resources. We then analyse how these deals affect social welfare for different instances of the basic framework and different interpretations of the concept of social welfare itself. In particular, we show how certain classes of deals are both sufficient and necessary to guarantee that a socially optimal allocation of resources will be reached eventually.

In this short paper we describe COCOS, a tool we are currently developing in order to account for the phenomenon of combining prototypical concepts, an open problem in the fields of AI and cognitive modelling. COCOS is based on a probabilistic extension of the logic of typicality ALC + T R by inclusions p :: T(C) D ("we have probability p that typical Cs are Ds") and it embeds a set of cognitive heuristics for concept combination.

In this work we present NERVOUS, an intelligent recommender system exploiting a probabilistic extension of a Description Logic of typicality to dynamically generate novel contents in AllMusic, a comprehensive and in-depth resource about music, providing data about albums, bands, musicians and songs (https://www.allmusic.com). The tool can be used for both the generation of novel music genres and styles, described by a set of typical properties characterizing them, and the reclassification of the available songs within such new genres.

Starting from the observation that rational closure has the undesirable property of being an "all or nothing" mechanism, we here propose a multipreferential semantics, which enriches the preferential semantics underlying rational closure in order to separately deal with the inheritance of different properties in an ontology with exceptions. We provide a multipreference closure mechanism which is sound with respect to the multipreference semantics.

In this work we present RAT-OWL, a Protégé 4.3 Plugin for reasoning about typicality in preferential Description Logics. RAT-OWL allows the user to reason in a nonmonotonic extension of Description Logics based on the notion of “rational closure”. This logic extends standard Description Logics in order to express “typical” properties, that can be directly specified by means of a typicality operator T: T(C) v D represents that “typical Cs are also Ds”. We show experimental results, indicating that the performances of RAT-OWL are promising.

We present a nonmonotonic extension of the Description Logic ALC for reasoning about prototypical properties and inheritance with exception. The logic ALC is extended by introducing a typicality operator T which is intended to select the "most normal" instances of a concept. A minimal model semantics is defined for ALC + T, in order to perform nonmonotonic inferences. The resulting logic ALC + Tmin is able to infer defeasible properties of explicit and implicit individuals. The paper presents a tableau calculus for deciding ALC + Tmin entailment. The work was partially supported by Regione Piemonte, Project ICT4Law. Main contribution of this paper have been also presented at the 11th European Conference on Logics in Artificial Intelligence "JELIA 2008" [10].

We show that global caching can be used with propagation of both satisfiability and unsatisfiability in a sound manner to give an EXPTIME algorithm for checking satisfiability w.r.t. a TBox in the basic description logic ALC. Our algorithm is based on a simple traditional tableau calculus which builds an and-or graph where no two nodes of the graph contain the same formula set. When a duplicate node is about to be created, we use the pre-existing node as a proxy, even if the proxy is from a different branch of the tableau, thereby building global caching into the algorithm from the start. Doing so is important since it allows us to reason explicitly about the correctness of global caching. We then show that propagating both satisfiability and unsatisfiability via the andor structure of the graph remains sound. We show that various search strategies can be used with global caching, including heuristics ones. To obtain a more efficient decision procedure for ALC, we apply several optimisation techniques. Of particular importance are the propagation of both satisfiability and unsatisfiability of a given node through the whole graph via subsetchecking between node contents. Another is the minimisation of unsatisfiable sets: that is, when the status of a node becomes unsatisfiable, we identify an (ideally minimal) inconsistent subset, and replace the content of the node with this "inconsistency" since the smaller set has a greater likelihood of propagating its unsatisfiability via subset-checking. We also use a dual procedure for maximising satisfiable sets. We do cutoffs for various search strategies, in particular, backjumping for depth-first search, by propagating "inconsistencies" and unsatisfiability through the and-or graph, and avoiding unnecessary expansions. By combining global caching, propagation and cutoffs, our framework reduces the search space more significantly than the framework of Donini and Massacci [3]. Also, the freedom to use arbitrary search heuristics significantly increases the application potential of our framework. National ICT Australia is funded by the Australian Government's Dept of Communications, Information Technology and the Arts and the Australian Research Council through Backing Australia's Ability and the ICT Centre of Excellence program.

Description logics are a family of knowledge representation formalisms that are descended from semantic networks and frames via the system KL-ONE. During the last decade, it has been shown that the important reasoning problems (like subsumption and satisfiability) in a great variety of description logics can be decided using tableau-like algorithms. This is not very surprising since description logics have turned out to be closely related to propositional modal logics and logics of programs (such as propositional dynamic logic), for which tableau procedures have been quite successful. Nevertheless, due to different underlying intuitions and applications, most description logics differ significantly from run-of-the-mill modal and program logics. Consequently, the research on tableau algorithms in description logics led to new techniques and results, which are, however, also of interest for modal logicians. In this article, we will focus on three features that play an important rôle in description logics (number restrictions, terminological axioms, and role constructors), and show how they can be taken into account by tableau algorithms.

Description logics class of knowledge representation formalisms r Descended from structured inheritance networks [Brachman 78]. r Tried to overcome ambiguities in semantic networks and frames that were due to their lack of a formal semantics. r Restriction to a small set of "epistemologically adequate" operators for defining concepts (classes). r Importance of well-defined basic inference procedures: subsumption and instance problem.

Membership queries extended with the meta query concept is proposed as a method to acquire complex classification rules. Furthermore, relevent concept classes, where a small number of queries is sufficient, are characterized. In this paper we advocate and present the benefits of the use of queries in order to learn a target concept efficiently. Thus providing the foundations for automating the knowledge acquisition process. Based on these results, we developed a knowledge acquisition tool KAC-Z which uses queries about specific domain objects. The systems usefulness has been demonstrated by its application in the domain of manufacturing (cutting) industry.

A significant number of Information Technology incidents are reported through email. To design and implement an intelligent incident management system, it is significant to automatically classify the reported incident to a given incident category. This requires the extraction of semantic content from the reported email text. In this research work, we have attempted to classify a reported incident to a given category based on its semantic content using ontology. We have developed an Incident Ontology that can serve as a knowledge base for the incident management system. We have also developed an automatic incident classifier that matches the semantical units of the incident report with concepts in the incident ontology. According to our evaluation, ontology-driven incident classification facilitates the process of Information Technology incident management in a better way since the model shows 100% recall, 66% precision, and 79% F1-Score for sample incident reports.

In recent years, there has been a growing interest in the application of foundational ontologies, i.e., formal ontological theories in the philosophical sense, to provide a theoretically sound foundation for improving the theory and practice of conceptual modeling. In this paper, we present advances on our research on the ontological foundations of conceptual modeling by addressing the concept of events. We present a foundational ontology of events (termed UFO-B) together with its axiomatization in first-order logic. Moreover, we report on an implementation of UFO-B using the computational logic language Alloy, and discuss its consistency, validation and possible uses.

When configuring customizable software, it is useful to provide interactive tool-support that ensures that the configuration does not breach given constraints. But, when is a configuration complete and how can the tool help the user to complete it? We formalize this problem and relate it to concepts from non-monotonic reasoning well researched in Artificial Intelligence. The results are interesting for both practitioners and theoreticians. Practitioners will find a technique facilitating an interactive configuration process and experiments supporting feasibility of the approach. Theoreticians will find links between well-known formal concepts and a concrete practical application.

We introduce a notion of rational closure for the logic SHIQ based on the well-known rational closure by Lehmann and Magidor [21]. We provide a semantic characterization of rational closure in SHIQ in terms of a preferential semantics, based on a finite rank characterization of minimal models.

Mediation is an important method in dispute resolution. We implement a case based reasoning approach to mediation integrating analogical and commonsense reasoning components that allow an artificial mediation agent to satisfy requirements expected from a human mediator, in particular: utilizing experience with cases in different domains; and structurally transforming the set of issues for a better solution. We utilize a case structure based on ontologies reflecting the perceptions of the parties in dispute. The analogical reasoning component, employing the Structure Mapping Theory from psychology, provides a flexibility to respond innovatively in unusual circumstances, in contrast with conventional approaches confined into specialized problem domains. We aim to build a mediation case base incorporating real world instances ranging from interpersonal or intergroup disputes to international conflicts.

Given a statistical database containing a set of summary tables, this paper examines the complexity of retrieving data from the database in order to satisfy a query. In particular, we consider the case when the query cannot be directly satisfied via a single summary table and requires two or more summary tables. We show that a system of linear equations can be constructed from a set of summary tables whose solution(s) satisfy a query in oarying degrees. We derive a formula for determining the degree of acceptabdity of the solution as a function of the characteristics of the summary tables which derive the algebraic system. We also show that selecting the optimal set of summary tables from the database that yields the best solution to the query is NP-complete. These findings offer important insights into the retrievabfit y of information from a statistical database when designing a statistical query processor.

Wikidata captures structured data on a number of subject domains, managing, among others, the information underlying Wikipedia and other Wikimedia projects. Wikidata serves as a repository of structured data, whose purpose is to support the consistent sharing and linking of data on the Web. To support these purposes, it is key that Wikidata is built on consistent data models and representation schemas, which are constructed and managed in a collaborative platform. In this paper, we address the quality of taxonomic hierarchies in Wikidata. We focus on taxonomic hierarchies with entities at different classification levels (particular individuals, types of individuals, types of types of individuals, etc.). We use an axiomatic theory for multi-level modeling to analyze current Wikidata content, and identify a significant number of problematic classification and taxonomic statements. The problems seem to arise from an inadequate use of instantiation and subclassing in certain Wikidata hierarchies. CCS Concepts • Collaborative and social computing systems and tools Wikis • Knowledge representation and reasoning.