Fundamenta Informaticae - Volume 23, issue 2-4

Authors: Perlis, Don

Article Type: Research Article

DOI: 10.3233/FI-1995-232349

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 145-148, 1995

Authors: Attardi, Guiseppe | Simi, Maria

Article Type: Research Article

Abstract: We present a formalisation for the notion of viewpoint, a construct meant for expressing several varieties of relativised truth. The formalisation consists in a logic which extends first order predicate calculus with its own metalanguage, an axiomatization of provability and proper reflection rules. The extension is not conservative, but consistency is granted. Viewpoints are defined as set of reified meta-level sentences. A proof theory for viewponts is developed which enables to carry out proofs of statements involving several viewpoints. A semantic account of viewpoints is provided, dealing with issues of self referential theories and paradoxes, and exploiting the notion of …contextual entailment. Notions such as beliefs, knowledge, absolute truth or truth relative to a situation can be uniformly modeled as provability in specialised viewpoints, obtained by imposing suitable constraints on viewpoints. Show more

DOI: 10.3233/FI-1995-232341

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 149-173, 1995

Authors: Besnard, Philippe | Schaub, Torsten

Article Type: Research Article

Abstract: In this paper, we elaborate the idea that contexts provide an important and meaningful notion in default reasoning. We demonstrate this by looking at Reiter's default logic that has been the prime candidate for formalizing consistency-based default reasoning ever since its introduction in 1980. This results in a new context-based approach to default logic, called contextual default logic. The approach extends the notion of a default rule and supplies each default extension with a context. In particular, contextual default logic provides a unified framework for default logics. That is, it allows for embedding existing variants of default logic along with …more traditional approaches like the closed world assumption. Since this is accomplished in a homogeneous way, we gain additional expressiveness by combining the diverse approaches. A key advantage of contextual default logic is that it provides a syntactical instrument for comparing existing default logics in a unified setting. In particular, the approach reveals that existing default logics mainly differ in the way they deal with an explicit or implicit underlying context. Show more

DOI: 10.3233/FI-1995-232342

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 175-223, 1995

Authors: Bhatnagar, Raj

Article Type: Research Article

Abstract: In this paper we present a formal view of an ‘imagination’ type of hypothesis generation process performed with the probabilistic knowledge of a domain. We outline a formalism for focused construction of interesting hypothetical situation-descriptions. Our formalism for the ‘imagining agent’ seeks to construct consistent, minimal, and desirable situation-descriptions by selecting suitable domain attributes and probabilistic dependency relationships from the available domain knowledge. An interestingness criterion made available to the imagining agent helps it in focusing its efforts towards ‘imagining’ only the interesting situation-descriptions.

DOI: 10.3233/FI-1995-232343

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 225-246, 1995

Authors: Bouquet, Paolo | Giunchiglia, Fausto

Article Type: Research Article

Abstract: One of the main problems in commonsense reasoning is the qualification problem, ie. the fact that the number of qualifications for most general commonsense statements is virtually infinite. In this paper we argue that a solution to this problem should be based on a (meta) conjecture that the theory used to reason about the world contains all the necessary information. We also show that this theory adequacy conjecture can be made before the application of any of the formalisms proposed in the past, eg. circumscription. Finally, we present a formalization of the solution proposed using contexts and circumscription and use …it to solve McCarthy's Glasgow-London-Moscow example. Show more

DOI: 10.3233/FI-1995-232344

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 247-262, 1995

Authors: Buvač, Saša | Buvač, Vanja | Mason, Ian A.

Article Type: Research Article

Abstract: In this paper we investigate the simple logical properties of contexts. We describe both the syntax and semantics of a general propositional language of context, and we give a Hilbert style proof system for this language. A propositional logic of context extends classical propositional logic in two ways. Firstly, a new modality, ist(κ,φ), is introduced. It is used to express that the sentence,φ, holds in the context, κ. Secondly, each context has its own vocabulary, i.e. a set of propositional atoms which are defined or meaningful in that context. The main results of this paper are the soundness and completeness …of this Hilbert style proof system. We also provide soundness and completeness results (i.e., correspondence theory) for various extensions of the general system. Finally, we prove that our logic is decidable, and give a brief comparison of our semantics to Kripke semantics. Show more

DOI: 10.3233/FI-1995-232345

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 263-301, 1995

Authors: Harper, Mary P. | Helzerman, Randall A.

Article Type: Research Article

Abstract: In this paper, we describe a system which is capable of utilizing a variety of knowledge sources to select the most appropriate parse for a spoken sentence. These knowledge sources include syntax, semantics, and contextual information. We discuss one way to utilize contextual information when determining the parse for a sentence. At its simplest level, the system can be thought of as a general-purpose query answering system for multiple topical databases. The user's input would be processed by the language processor which interfaces to the databases with the goal of interacting with the correct database in order to provide a …reasonable answer to the user's spoken request. Initially, it analyzes a word graph of sentence hypotheses provided by a speech recognizer using general syntactic and semantic rules. Then, if the utterance is still ambiguous, it utilizes context-specific constraints to further refine the analysis. This brings us closer to developing a more general purpose interface for multiple databases. Show more

DOI: 10.3233/FI-1995-232346

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 303-353, 1995

Authors: Miller, Michael

Article Type: Research Article

Abstract: Context plays a crucial role in natural-language dialogues. But context can change over the course of a dialogue, and thus communicating agents are tasked with identifying and keeping track of context shifts in order to understand conversations. But context is not wholly objective; each participant in a dialogue has her own view of context. At times the parties involved in a dialogue will unknowingly presume different (aspects of) contexts from one another, perhaps because one person has not kept up with the other's most recent context shift. The resulting context clash may lead to confusion or miscommunication. Agents must be …prepared to sort out these confusions when they become evident. Active logics can be successfully utilized by an agent facing confusions such as those that arise when a context clash leads her to misidentify an object. In this paper the active logic approach to resolving such effects of a context clash is sketched. The agent's misidentification is initially reflected in her beliefs, and belief revision is later used to resolve this effect of the clash. As theoretical tools active logics have proven useful for solving a varied array of commonsense reasoning problems, but with implementation comes space and time complexity concerns. These are also discussed along with a proposed partial remedy based in part on context or focus-of-attention. Show more

DOI: 10.3233/FI-1995-232347

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 355-370, 1995

Authors: Nirkhe, Madhura | Kraus, Sarit

Article Type: Research Article

Abstract: Formal real-time imagination is a term that may curiously describe the activities of a commonsense agent in a real-time setting in general, and in a tight deadline situation in particular. We briefly describe an ‘active-logic’ mechanism that fits this description. Temporal projection is an essential component of realtime planning. We draw a parallel between imagination as we understand it in human context and the capacity of the automated agent to formulate mental images of possible scenarios and plans of action in the course of its reasoning. We outline a treatment of temporal issues of significance to a time-situated reasoning mechanism …in a dynamic setting with deadlines. The Yale shooting problem is a benchmark problem in temporal reasoning. We demonstrate how the active-logic planning mechanism successfully handles some interesting real-time variants of the Yale shooting problem. The solutions to each of these illustrate the agent’s ability to form contexts within which to reason, to project in each context thus formed by applying default inferences, and to revise and extend its conclusions within each context by applying time-sensitive inference rules, and most importantly, to account for all the time spent in the process. Show more

DOI: 10.3233/FI-1995-232348

Citation: Fundamenta Informaticae, vol. 23, no. 2-4, pp. 371-394, 1995