Fundamenta Informaticae - Volume 31, issue 3-4

Authors: Banerjee, Mohua

Article Type: Research Article

Abstract: A propositional logic for rough sets was proposed in [2]. The present work establishes a relationship between the finitary fragment of this logic and 3-valued Lukasiewicz logic ℒ3. It is also observed that there is an embedding from ℒ3 into the modal system S5 .

Keywords: Rough set theory, Algebraic logic, 3-valued Lukasiewicz logic, Modal system S5

DOI: 10.3233/FI-1997-313401

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 213-220, 1997

Authors: Brewka, Gerhard | Gottlob, Georg

Article Type: Research Article

Abstract: Default logic is one of the most popular approaches to model defeasible reasoning. Nevertheless, there are a number of problems with Reiter's original semantics that have led to the investigation of alternative approaches. In particular, Baral/Subrahmanian and Przymusinska/Przymusinski have investigated generalizations of well-founded semantics for normal logic programs to default logic. These generalizations have a number of interesting properties. Unfortunately, it turns out that in many realistic situations they are unable to draw any defeasible conclusions at all - which can hardly be viewed as satisfactory. We show how this difficulty can be solved by varying the fixed point operator …underlying the semantics. We define a range of different semantics. All of them are correct wrt. safe conclusions under Reiter semantics, i.e. those conclusions with the same proof in all extensions. For the strongest semantics we have also completeness in the case of coherent default theories, i.e. default theories with at least one extension. The logics differ in the effort spent for determining potential conclusions. It turns out that they are at least as complex as original default logic. We show that our approach also leads to new semantics for normal and extended logic programs. Moreover, we define prioritized versions of the logics. Show more

Keywords: Nonmonotonic reasoning, default logic, well-founded semantics

DOI: 10.3233/FI-1997-313402

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 221-236, 1997

Authors: Burkhard, Hans-Dieter

Article Type: Research Article

Abstract: Mental attributes of agents are investigated in a framework of transition systems and abstract languages. The mental attitudes are related to beliefs, desires/goals and intentions/plans which are known from so-called BDI-architectures. Actions and events are more stressed than states. This allows the consideration of global and individual aspects of belief, desire, intentions etc. in a simple unified formalism.

Keywords: Agent-Oriented Programming, Multi-Agent Systems, BDI-Architecture

DOI: 10.3233/FI-1997-313403

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 237-252, 1997

Authors: Chitil, Olaf

Article Type: Research Article

Abstract: A comprehensive semantics for functional programs is presented, which generalizes the well-known call-by-value and call-by-name semantics. By permitting a separate choice between call-by value and call-by-name for every argument position of every function and parameterizing the semantics by this choice we abstract from the parameter-passing mechanism. Thus common and distinguishing features of all instances of the ζ-semantics, especially call-by-value and call-by-name semantics, are highlighted. Furthermore, a property can be validated for all instances of the ζ-semantics by a single proof. This is employed for proving the equivalence of the given denotational (fixed-point based) and two operational (reduction based) definitions of …the ζ-semantics. We present and apply means for very simple proofs of equivalence with the denotational ζ-semantics for a large class of reduction-based ζ-semantics. Our basis are simple first-order constructor-based functional programs with patterns. Show more

Keywords: functional programming language, denotational and operational semantics, call-by-value, call-by-name, strictness, pattern-matching

DOI: 10.3233/FI-1997-313404

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 253-294, 1997

Authors: Deneva, Ana | Vakarelov, Dimiter

Article Type: Research Article

DOI: 10.3233/FI-1997-313405

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 295-304, 1997

Authors: Maggiolo-Schettini, Andrea | Matteucci, Gionata

Article Type: Research Article

Abstract: Cause-Effect (C-E) structures have been proposed as a formalism to describe concurrent and distributed systems. On C-E structures two operations, multiplication and addition, are defined, which allow easy combination and modular development of descriptions. In this paper a concept of process of a C-E structure with an initial state (C-E system) is defined similarly to that of a process of a Condition/Event net in Petri net theory, and operations on processes are studied which correspond to operations on C-E systems.

Keywords: Cause-Effect systems, Processes, Process combination

DOI: 10.3233/FI-1997-313406

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 305-335, 1997

Authors: Maggiolo-Schettini, Andrea | Winkowski, Józef

Article Type: Research Article

Abstract: A model of processes of transforming graphs is proposed in which concurrency and branching can be represented. Operations on structures representing processes of transforming graphs are defined that allow one to construct such structures from simple components and to characterize sets of processes of transforming graphs, including sets of processes generated by graph grammars.

Keywords: graph, occurrence structure, dynamic graph, application of a dynamic graph to a graph, concatenation of dynamic graphs, sum of dynamic graphs, production, derivation, graph grammar

DOI: 10.3233/FI-1997-313407

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 337-355, 1997

Authors: Montanari, Ugo | Ristori, Gioia

Article Type: Research Article

Abstract: In [5, 8] a compositional, algebraic framework is provided in which shared memory systems can be specified and analyzed. The interferences in the use of the shared data are modelled, at the abstract level, by a conflict relation among the actions of the system. The semantic model of the process algebra language is defined in such a way that conflicting actions cannot be executed in parallel, whilst independent actions can. We show in the paper that conflict-based semantics do not allow for exploiting all the parallelism among the activities of a system. Actually, there are functionally equivalent programs (i.e. programs …that compute the same final states of the activities and data) which perform conflicting actions in different order. In these situations, conflict-based semantics are not satisfactory, since they put useless sequential constraints on the executions. In this paper we define a concurrent semantics for the process algebra language in [5] which is in agreement with functional equivalence. We propose a model for the language which embeds both concurrent and functional aspects of programs, and takes into account two fundamental topics: the enhancement of the parallelism among the activities of the system, and the functional correctness of its computations. The formalism we use is that of Contextual Condition Event nets [12] (CC/E nets). By using CC/E nets we provide a faithful description of both the data and the activities of a shared memory system, in such a way that each process algebra term can be described by means of a set of net computations. The concurrent semantics of a term is then obtained by associating a structure called O-process [4] with each net computation. This semantics is in full agreement with functional equivalence, i.e. two process algebra terms compute the same final states of the activities and data if and only if they have the same concurrent semantics. Show more

DOI: 10.3233/FI-1997-313408

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 357-377, 1997

Authors: Rey, Jean-François

Article Type: Research Article

Abstract: This paper introduces the notion of block product of two categories. It is the first step in the working out of a useful definition of the block product of two C-varieties which is needed for the theory of decompositions of monoids by means of wreath or block products. The construction of the block product of two categories is a particular case of a more general notion: the strong semidirect product of an action. In this first part of a two parts work we define the strong semidirect product functor and give some properties of this functor with respect to Tilson's …division. In the second part we construct a left adjoint of the strong semidirect product functor and we define the kernel of a relational morphism of categories. With these notions we define the block product of two C-varieties and prove a kernel theorem in the category settings which extends a work of J. Rhodes and B. Tilson. Show more

DOI: 10.3233/FI-1997-313409

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 379-400, 1997

Authors: Rey, Jean-François

Article Type: Research Article

Abstract: This paper introduces the notion of the kernel of a relational morphism of categories. This is the second step in the working out of a useful definition of the block product of two C-varieties which in turn is needed for the theory of decompositions of monoids by means of wreath or block products. In a previous work, the author defined the construction of the block product of two categories and the strong semidirect product functor. In this second part, we construct a left adjoint of the strong semidirect product functor which is the starting point of our construction of the …kernel of a relational morphism. With these notions we define the block product of two C-varieties and prove a kernel theorem in the category settings which extends a work of J. Rhodes and B. Tilson. Show more

DOI: 10.3233/FI-1997-313410

Citation: Fundamenta Informaticae, vol. 31, no. 3-4, pp. 401-421, 1997