In allocation problems with indivisible goods, money compensation is used to distribute worth in a fair way. Coalitional games provide a formal mathematical framework to model such problems, and the Shapley value is a solution concept widely used to realise a fair distribution. To overcome its intractability, we describe how to simplify allocation problems and we propose algorithms for computing lower bounds and upper bounds of the Shapley value that can be combined with approximation algorithms. The proposed techniques have been implemented and tested on a real-world application of allocation problems, namely, the Italian research assessment program known as VQR.

Temporal Logic Model Checking is a verification method in which we describe a system, the model, and then we verify whether important properties, expressed in a temporal logic formula, hold in the system. Many Model Checking tools employ BDDs or some other data structure to represent sets of states. It has been empirically observed that the BDDs used in these algorithms may grow exponentially as the model and formula increase in size. We formally prove that no kind of data structure of polynomial size can represent the set of valid initial states for all models and all formulae. This result holds for all data structures where a state can be checked in polynomial time. Therefore, it holds not only for all types of BDDs regardless of variable ordering, but also for more powerful data structures, such as RBCs, MTBDDs, ADDs and SDDs. Thus, the size explosion of BDDs is not a limit of these specific data representation structures, but is unavoidable: every formalism used in the same way would lead to an exponential size blow up.

In this paper, we present an efficient method for detecting collisions and self-collisions on articulated models deformed by Position Based Skinning. Position Based Skinning is a real-time skinning method, which produces believable skin deformations, and avoids artifacts such as the well-known " candy-wrapper " effect and joint-bulging. The proposed method employs spatial hashing with a uniform grid to detect collisions and self collisions. All the mesh primitives are mapped to a hash table, where only primitives mapped to the same hash index indicate a possible collision and need to be tested for intersections. Being based on spatial hashing, our method requires neither expensive set-up nor complex data structures and is hence suitable for articulated characters with deformable soft tissues. We exploit the skeletal nature of the deformation to only update the hash table when required. The resulting algorithm is simple to implement and fast enough for real-time applications. We demonstrate the efficiency of our method on various animation examples. A quantitative experiment is also presented to evaluate our method.

Abduction is one of the most important forms of reasoning; it has been successfully applied to several practical problems, such as diagnosis. In this article we investigate whether the computational complexity of abduction can be reduced by an appropriate use of preprocessing. This is motivated by the fact that part of the data of the problem (namely, the set of all possible assumptions and the theory relating assumptions and manifestations) is often known before the rest of the problem. In this article, we show some complexity results about abduction when compilation is allowed.

In this paper, we define and study the k-approximating circuits. A circuit accepting a given set of inputs A is k-approximated by accepting inputs that lifter from one of A by at most k bits. We show that the existence of polynomial-size k-approximating circuits depends on the relation between k and the number of inputs.

We argue that essential facets of Web services, and especially those useful to understand their interaction, can be described using process-algebraic notations. Web service description and execution languages such as BPEL are essentially process description languages; they are based on primitives for behaviour description and message exchange which can also be found in more abstract process algebras. One legitimate question is therefore whether the formal approach and the sophisticated tools introduced for process algebra can be used to improve the effectiveness and the reliability of Web service development. Our investigations suggest a positive answer, and we claim that process algebras provide a very complete and satisfactory assistance to the whole process of Web service development. We show on a case study that readily available tools based on process algebra are effective at verifying that Web services conform to their requirements and respect properties. We advocate their use both at the design stage and for reverse engineering issues. More prospectively, we discuss how they can be helpful to tackle choreography issues.

We investigate the space efficiency of a Propositional Knowledge Representation (PKR) formalism. Intuitively, the space efficiency of a formalism F in representing a certain piece of knowledge A, is the size of the shortest formula of F that represents A. In this paper we assume that knowledge is either a set of propositional interpretations (models) or a set of propositional formulae (theorems). We provide a formal way of talking about the relative ability of PKR formalisms to compactly represent a set of models or a set of theorems. We introduce two new compactness measures, the corresponding classes, and show that the relative space efficiency of a PKR formalism in representing models/theorems is directly related to such classes. In particular, we consider formalisms for nonmonotonic reasoning, such as circumscription and default logic, as well as belief revision operators and the stable model semantics for logic programs with negation. One interesting result is that formalisms with the same time complexity do not necessarily belong to the same space efficiency class.

Knowledge-based systems must be able to "intelligently" manage a large amount of information coming from different sources and at different moments in time. Intelligent systems must be able to cope with a changing world by adopting a "principled" strategy. Many formalisms have been put forward in the artificial intelligence (AI) and database (DB) literature to address this problem. Among them, belief revision is one of the most successful frameworks to deal with dynamically changing worlds. Formal properties of belief revision have been investigated by Alchourron, Gardenfors, and Makinson, who put forward a set of postulates stating the properties that a belief revision operator should satisfy. Among these properties, a basic assumption of revision is that the new piece of information is totally reliable and, therefore, must be in the revised knowledge base. Different principles must be applied when there are two different sources of information and each one has a different view of the situation-the two views contradicting each other. If we do not have any reason to consider any of the sources completely unreliable, the best we can do is to "merge" the two views in a new and consistent one, trying to preserve as much information as possible. We call this merging process arbitration. In this paper, we investigate the properties that any arbitration operator should satisfy. In the style of Alchourron, Gardenfors, and Makinson we propose a set of postulates, analyze their properties, and propose actual operators for arbitration.

Article Free Access Share on The size of a revised knowledge base Authors: Marco Cadoli Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, Italy Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, ItalyView Profile , Francesco M. Donini Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, Italy Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, ItalyView Profile , Paolo Liberatore Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, Italy Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, ItalyView Profile , Marco Schaerf Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, Italy Dipartimento di Informatica e Sistemistica, Università di Roma 'La Sapienza', via Salaria 113, I-00198, Roma, ItalyView Profile Authors Info & Claims PODS '95: Proceedings of the fourteenth ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systemsMay 1995 Pages 151–162https://doi.org/10.1145/212433.220205Published:22 May 1995Publication History 12citation198DownloadsMetricsTotal Citations12Total Downloads198Last 12 Months2Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

We propose a technique for dealing with the high complexity of reasoning under propositional default logic and circumscription. The technique is based on the notion of approximation: A logical consequence relation is computed by means of sound and progressively “more complete” relations, as well as complete and progressively “more sound” ones. Both sequences generated in this way converge to the original consequence relation and are easier to compute. Moreover they are given a clear semantics based on multivalued logic. With this technique unsoundness and incompleteness are introduced in a controlled way and precisely characterized.

We propose a technique for dealing with the high complexity of reasoning under propositional default logic and circumscription. The technique is based on the notion of approximation: A logical consequence relation is computed by means of sound and pr

Two main approaches have been followed in the literature to give a semantics to non-Horn databases. The first one is based on considering the set of rules composing the programs as inference rules and interpreting the negation in the body as failure to prove. The other approach is based on the so-called closed-world assumption and its objective is to define a stronger notion of consequence from a theory than the classical one, where, very roughly, negative information can be inferred whenever its positive counterpart cannot be deduced from the theory. In this work we generalize the semantics for negation in logic programs, putting together the constructive nature of the rule-based deductive databases with the syntax-independence of the closed-world reasoning rules. These generalized semantics are shown to be a well-motivated and well-founded alternative to closed-world assumptions since they enjoy nice semantic and computational properties.

The use of multivalued logics for knowledge representation and nonmonotonic reasoning has often been advocated, in particular within the general framework proposed by Ginsberg in his paper “Multivalued logics: a uniform approach to reasoning in artificial intelligence.” His system is based on a multivalued logic with an arbitrary number of truth values classified with respect to two partial orders, a truth order and a knowledge order. This classification is very interesting and gives an intuitive appeal to the framework. In this paper the work by Ginsberg is critically reviewed, pointing out some flaws and ways to overcome them. Moreover, we present some ideas on how to modify the original schema in order to obtain a more semantically well‐founded framework. L'utilisation de la Iogique multivalente pour la représentation des connaissances et le raisonnement non monotone a souvent été préconisée, en particulier à l'intérieur du cadre général proposé par Ginsberg dans son article intitulé? Multivalued logics: a uniform approach to reasoning in artificial intelligence ? Son système est basé sur une logique multivalente comportant un nombre arbitraire de valeurs de vérité classées selon deux ordres partiels: un ordre de vérité et un ordre de connaissances. Cette classification est très intéressante et donne un attrait intuitif au cadre. Dans cet article, l'auteur examine le travail de Ginsberg, y relève des lacunes et propose des moyens de les corriger. De plus, il expose certaines idées en vue de modifier le schéma original et ainsi obtenir un meilleur cadre du point de vue de la sémantique.